Research Selected Recent Research Publications
 

Hole Contacts on Transition Metal Dichalcogenides: Interface Chemistry and Band Alignments

Stephen McDonnell , Angelica Azcatl , Rafik Addou ,Cheng Gong , Corsin Battaglia§, Steven Chuang§,Kyeongjae Cho , Ali Javey§, and Robert M. Wallace

Electrical Engineering and Computer Sciences and§Berkeley Sensor and Actuator Center, University of California, Berkeley, California 94720, United States
 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720,United States

Department of Materials Science and Engineering,The University of Texas at Dallas, Richardson, Texas 75080, United States

MoOx shows promising potential as an efficient hole injection layer for p-FETs based on transition metal dichalcogenides. A combination of experiment and theory is used to study the surface and interfacial chemistry as well as the band alignments for MoOx/MoS2 and MoOx/WSe2 heterostructures, using photoelectron spectroscopy, scanning tunneling microscopy and density functional theory. A Mo5+ rich interface region is identified and is proposed to explain the similar low hole Schottky barriers reported in a recent device study utilizing MoOx contacts on MoS2 and WSe2.

[http://dx.doi.org/10.1021/nn501728w]

 

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Nano LettersNano Lett., 2014, 14 (3), pp 1337–1342

MoS2 P-type Transistors and Diodes Enabled by High Work Function MoOxContacts

Electrical Engineering and Computer Sciences and§Berkeley Sensor and Actuator Center, University of California, Berkeley, California 94720, United States
 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720,United States
 Department of Materials Science and Engineering,The University of Texas at Dallas, Richardson, Texas 75080, United States

The development of low-resistance source/drain contacts to transition-metal dichalcogenides (TMDCs) is crucial for the realization of high-performance logic components. In particular, efficient hole contacts are required for the fabrication of p-type transistors with MoS2, a model TMDC. Previous studies have shown that the Fermi level of elemental metals is pinned close to the conduction band of MoS2, thus resulting in large Schottky barrier heights for holes with limited hole injection from the contacts. Here, we show that substoichiometric molybdenum trioxide (MoOx, x < 3), a high work function material, acts as an efficient hole injection layer to MoS2 and WSe2. In particular, we demonstrate MoS2 p-type field-effect transistors and diodes by using MoOx contacts. We also show drastic on-current improvement for p-type WSe2 FETs with MoOx contacts over devices made with Pd contacts, which is the prototypical metal used for hole injection. The work presents an important advance in contact engineering of TMDCs and will enable future exploration of their performance limits and intrinsic transport properties.

[http://dx.doi.org/10.1021/nl4043505]

 

 

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Nano LettersNano Lett., 2014, 14 (2), pp 967–971

Hole Selective MoOx Contact for Silicon Solar Cells

Corsin Battaglia †‡, Xingtian Yin †‡§, Maxwell Zheng †‡, Ian D. Sharp , Teresa Chen , Stephen McDonnell , Angelica Azcatl , Carlo Carraro #, Biwu Ma , Roya Maboudian #, Robert. M. Wallace , and Ali Javey *†‡

 Electrical Engineering and Computer Sciences Department, University of California, Berkeley, California 94720, United States
 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720,United States
§ Electronic Materials Research Laboratory, Xi’an Jiaotong University, Xi’an, 710049 Shaanxi, People’s Republic of China
 Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
Materials Science and Engineering, University of Texas, Dallas, Texas 75083, United States
# Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720, United States

Using an ultrathin (15 nm in thickness) molybdenum oxide (MoOx, x < 3) layer as a transparent hole selective contact to n-type silicon, we demonstrate a room-temperature processed oxide/silicon solar cell with a power conversion efficiency of 14.3%. While MoOx is commonly considered to be a semiconductor with a band gap of 3.3 eV, from X-ray photoelectron spectroscopy we show that MoOx may be considered to behave as a high workfunction metal with a low density of states at the Fermi level originating from the tail of an oxygen vacancy derived defect band located inside the band gap. Specifically, in the absence of carbon contamination, we measure a work function potential of 6.6 eV, which is significantly higher than that of all elemental metals. Our results on the archetypical semiconductor silicon demonstrate the use of nm-thick transition metal oxides as a simple and versatile pathway for dopant-free contacts to inorganic semiconductors. This work has important implications toward enabling a novel class of junctionless devices with applications for solar cells, light-emitting diodes, photodetectors, and transistors.

[http://dx.doi.org/0.1021/nl404389u]

 

APPLIED PHYSICS LETTERS 104, 111601 (2014)

MoS2 functionalization for ultra-thin atomic layer deposited dielectrics

Angelica Azcatl, Stephen McDonnell, Santosh K. C., Xin Peng, Hong Dong, Xiaoye Qin, Rafik Addou, Greg I. Mordi, Ning Lu, Jiyoung Kim, Moon J. Kim, Kyeongjae Cho, and    Robert M. Wallace

Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080, USA

(Received 28 December 2013; accepted 9 March 2014; published online 19 March 2014)

The effect of room temperature ultraviolet-ozone (UV-O3) exposure of MoS2 on the uniformity of subsequent atomic layer deposition of Al2O3 is investigated. It is found that a UV-O3 pre-treatment removes adsorbed carbon contamination from the MoS2 surface and also functionalizes the MoS2 surface through the formation of a weak sulfur-oxygen bond without any evidence of molybdenum-sulfur bond disruption. This is supported by first principles density functional theory calculations which show that oxygen bonded to a surface sulfur atom while the sulfur is simultaneously back-bonded to three molybdenum atoms is a thermodynamically favorable configuration. The adsorbed oxygen increases the reactivity of MoS2 surface and provides nucleation sites for atomic layer deposition of Al2O3. The enhanced nucleation is found to be dependent on the thin film deposition temperature.

© 2014 AIP Publishing LLC.

[http://dx.doi.org/10.1063/1.4869149]

 

 

 

Defect-Dominated Doping and Contact Resistance in MoS2

Stephen McDonnell, Rafik Addou, Creighton Buie, Robert M. Wallace, and Christopher L. Hinkle

ABSTRACT Achieving low resistance contacts is vital for the realization of nanoelectronic devices based on transition metal dichalcogenides. We find that intrinsic defects in MoS2 dominate the metal/MoS2 contact resistance and provide a low Schottky barrier independent of metal contact work function. Furthermore, we show that MoS2 can exhibit both n-type and p-type conduction at different points on a same sample. We identify these regions independently by complementary characterization techniques and show how the Fermi level can shift by 1 eV over tens of nanometers in spatial resolution. We find that these variations in doping are defect-chemistry-related and are independent of contact metal. This raises questions on previous reports of metal-induced doping of MoS2 since the same metal in contact with MoS2 can exhibit both n- and p-type behavior. These results may provide a potential route for achieving low electron and hole Schottky barrier contacts with a single metal deposition.

© 2013 American Chemical Society

DOI: 10.1021/nn500044q

 

 

 

 

 

ACS Nano, 8, 642 (2014)

Realistic Metal-Graphene Contact Structures

Cheng Gong, Stephen McDonnell, Xiaoye Qin, Angelica Azcatl, Hong Dong, Yves J. Chabal, Kyeongjae Cho, and Robert M. Wallace

ABSTRACT The contact resistance of metal-graphene junctions has been actively explored and exhibited inconsistencies in reported values. The interpretation of these electrical data has been based exclusively on a side-contact model, that is, metal slabs sitting on a pristine graphene sheet. Using in situ X-ray photoelectron spectroscopy to study the wetting of metals on as synthesized graphene on copper foil, we show that side-contact is sometimes a misleading picture. For instance, metals like Pd and Ti readily react with graphitic carbons, resulting in Pd- and Ti-carbides. Carbide formation is associated with C-C bond breaking in graphene, leading to an end-contact geometry between the metals and the periphery of the remaining graphene patches. This work validates the spontaneous formation of the metal-graphene end-contact during the metal deposition process as a result of the metal-graphene reaction instead of a simple carbon diffusion process.

© 2013 American Chemical Society

DOI: 10.1021/nn405249n

 

 

 

 

 

 

 

INVITED REVIEW

PROCEEDINGS OF THE  IEEE 101(7), 1536 (2013)

Graphene Growth and Device Integration

This paper describes one of the emerging methods for growing graphene-the chemical vapor deposition method-which is based on a catalytic reaction between a carbon precursor and a metal substrate such as Ni, Cu, and Ru, to name a few.

By Luigi Colombo, Fellow IEEE, Robert M. Wallace, Fellow IEEE, and Rodney S. Ruoff

Graphene has been introduced to the electronics community as a potentially useful material for scaling electronic devices to meet low-power and high-performance targets set by the semiconductor industry international roadmap, radio-frequency (RF) devices, and many more applications. Growth and integration of graphene for any device is challenging and will require significant effort and innovation to address the many issues associated with integrating the monolayer, chemically inert surface with metals and dielectrics. In this paper, we review the growth and integration of graphene for simple field-effect transistors and present physical and electrical data on the integrated graphene with metals and dielectrics.

© 2013 IEEE  DOI:  10.1109/JPROC.2013.2260114

 

 

 

 

JOURNAL OF APPLIED PHYSICS 113, 244102 (2013)

In situ atomic layer deposition study of HfO2 growth on NH4OH and atomic hydrogen treated Al0.25Ga0.75N

Xiaoye Qin, Barry Brennan, Hong Dong, Jiyoung Kim, Christopher L. Hinkle, and Robert M. Wallace

Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080, USA

(Received 6 March 2013; accepted 10 June 2013; published online 26 June 2013)

The atomic layer deposition (ALD) of HfO2 on the native oxide, NH4OH, and atomic hydrogen treated Al0.25Ga0.75N surface was studied using in situ X-ray photoelectron spectroscopy (XPS), after each individual “half cycle” of the ALD process. During the deposition process, minimal change in the chemical states of Ga and Al is detected, with no evidence of interfacial oxide generation. The initial HfO2 growth rate on the native oxide Al0.25Ga0.75N surface is very low, however, exposure of the Al0.25Ga0.75N surface to atomic hydrogen decreases the concentration of carbon and oxygen and enhances the HfO2 growth rate.

 © 2013 AIP Publishing LLC. DOI: 10.1063/1.4812243

 

 

 

 

APPLIED PHYSICS LETTERS 102, 131602 (2013)

Surface and interfacial reaction study of half cycle atomic layer deposited HfO2 on chemically treated GaSb surfaces

D. M. Zhernokletov,1 H. Dong,2 B. Brennan,2 M. Yakimov,3 V. Tokranov,3 S. Oktyabrsky,3 J. Kim,2 and R. M. Wallace1,2

1Department of Physics, University of Texas at Dallas, Richardson, Texas 75080, USA

2Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080, USA

3College of Nanoscale Science and Engineering, University at Albany – SUNY, Albany, New York 12203, USA

(Received 20 December 2012; accepted 21 March 2013; published online 4 April 2013)

An in situ half-cycle atomic layer deposition/X-ray photoelectron spectroscopy (XPS) study was conducted in order to investigate the evolution of the HfO2 dielectric interface with GaSb(100) surfaces after sulfur passivation and HCl etching, designed to remove the native oxides. With the first pulses of tetrakis(dimethylamido)hafnium(IV) and water, a decrease in the concentration of antimony oxide states present on the HCl-etched surface is observed, while antimony sulfur states diminished below the XPS detection limit on sulfur passivated surface. An increase in the amount of gallium oxide/sulfide is seen, suggesting oxygen or sulfur transfers from antimony to gallium during antimony oxides/sulfides decomposition.

© 2013 American Institute of Physics. DOI: 10.1063/1.4800441

 

 

 

APPLIED PHYSICS LETTERS 100, 151603 (2012)

In situ surface pre-treatment study of GaAs and In0.53Ga0.47As

B. Brennan, D. M. Zhernokletov, H. Dong, C. L. Hinkle, J. Kim, and R. M. Wallace

Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080, USA

(Received 23 February 2012; accepted 26 March 2012; published online 10 April 2012

The impact of using multiple cycles of trimethyl-aluminum (TMA) prior to Al2O3 deposition on the properties of (NH4)2S treated In0.53Ga0.47As and GaAs substrates was investigated by in situ x-ray photoelectron spectroscopy. Increasing the number of TMA cycles prior to Al2O3 atomic layer deposition (ALD) was seen to decrease the concentration of As-As detected at the oxide-semiconductor interface. The impact of annealing the (NH4)2S treated GaAs surface in situ prior to ALD, in various environments, was also investigated.

© 2012 American Institute of Physics DOI: 10.1063/1.3702885

 

 

 

ACS NANO 6(4), 3224 (2012)

Reducing Extrinsic Performance- Limiting Factors in Graphene Grown by Chemical Vapor Deposition

Jack Chan, Archana Venugopal, Adam Pirkle, Stephen McDonnell, David Hinojos, Carl W. Magnuson, Rodney S. Ruoff, Luigi Colombo,  Robert M. Wallace, and Eric M. Vogel

Department of Materials Science and Engineering, University of Texas at Dallas, 800 West Campbell Road, Richardson, TX 75080, USA.
Department of Mechanical Engineering and Materials Science and Engineering Program, University of Texas at Austin, One University Station C2200, Austin, TX 78712, USA.

Field-effect transistors fabricated on graphene grown by chemical vapor deposition (CVD) often exhibit large hysteresis accompanied by low mobility, high positive backgate voltage corresponding to the minimum conductivity point (Vmin), and high intrinsic carrier concentration (n0). In this report, we show that the mobility reported to date for CVD graphene devices on SiO2 is limited by trapped water between the graphene and SiO2 substrate, impurities introduced during the transfer process and adsorbates acquired from the ambient. We systematically study the origin of the scattering impurities and report on a process which achieves the highest mobility (μ) reported to date on large-area devices for CVD graphene on SiO2: maximum mobility (μmax) of 7800 cm2 /(Vs) measured at room temperature and 12 700 cm2/(Vs) at 77 K. These mobility values are close to those reported for exfoliated graphene on SiO2 and can be obtained through the careful control of device fabrication steps including minimizing resist residue and non-aqueous transfer combined with annealing. It is also observed that CVD graphene is prone to adsorption of atmospheric species, and annealing at elevated temperature in vacuum helps remove these species.

2012 American Chemical Society   DOI: 10.1021/nn300107f

 

 

APPLIED PHYSICS LETTERS 100, 141606 (2012)

Interfacial oxide re-growth in thin film metal oxide III-V semiconductor systems

S. McDonnell, H. Dong, J. M. Hawkins, B. Brennan, M. Milojevic, F. S. Aguirre-Tostado, D. M. Zhernokletov, C. L. Hinkle, J. Kim, and R. M. Wallace

Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080 USA

(Received 20 February 2012; accepted 17 March 2012; published online 4 April 2012)

The Al2O3/GaAs and HfO2/GaAs interfaces after atomic layer deposition are studied using in situ monochromatic x-ray photoelectron spectroscopy. Samples are deliberately exposed to atmospheric conditions and interfacial oxide re-growth is observed. The extent of this re-growth is found to depend on the dielectric material and the exposure temperature. Comparisons with previous studies show that ex situ characterization can result in misleading conclusions about the interface reactions occurring during the metal oxide deposition process.

©  2012 American Institute of Physics. DOI: 10.1063/1.3700863

 

 

 

SCIENCE 24 June 2011:
Vol. 332 no. 6037 pp. 1537-1541

REPORT

Carbon-Based Supercapacitors Produced by Activation of Graphene

Department of Mechanical Engineering and Materials Science and Engineering Program, University of Texas at Austin, One University Station C2200, Austin, TX 78712, USA.
Department of Materials Science and Engineering, University of Texas at Dallas, 800 West Campbell Road, Richardson, TX 75080, USA.
Quantachrome Instruments, 1900 Corporate Drive, Boynton Beach, FL 33426, USA.
Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973, USA

Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxygen and hydrogen content. This sp2-bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.

© 2011 American Association for the Advancement of Science DOI: 10.1126/science.1200770

 

 

 

 

 

Current Opinion in Solid State and Materials Science (in press)

Invited Review

Interfacial chemistry of oxides on InxGa(1-x)As and implications for MOSFET applications

C.L. Hinkle, E.M. Vogel, P.D. Ye, R.M. Wallace

Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, TX 75044, USA

School of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, IN 47907, USA

The prospect of enhanced device performance from III–V materials has been recognized for at least 50 years, and yet, relative to the phenomenal size of the Si-based IC industry, these materials fulfilled only specific niches and were often referred to as ‘‘the material of the future’’ . A key restriction enabling widespread use of III–V materials is the lack of a high quality, natural insulator for III–V substrates like that available for the SiO2/Si materials system . The prospect of impending scaling challenges for technologies based on silicon metal oxide semiconductor field effect transistor (MOSFET) devices has brought renewed focus on the use of alternate surface channel materials from the III–V compound semiconductor family. The performance of the traditional MOSFET device structure is dominated by defects at the semiconductor/oxide interface, which in turn requires a high quality semiconductor surface. In this review, reflecting the authors’ current opinion, the recent progress in the understanding of the dielectric/III–V interface is summarized, particularly in regard to the interfacial chemistry that impacts the resultant electrical behavior observed. The first section summarizes the nature of the oxidation states of surface oxides on InxGa1-xAs. Then the atomic layer deposition of such oxides on the InxGa1-xAs surface is summarized in view of the interfacial chemical reactions employed. Finally the resultant electrical properties observed are examined, including the effects of substrate orientation. Portions of this review have been published previously.

 © 2011 Elsevier Ltd., DOI: 10.1016/j.cossms.2011.04.005

 

 

 

APPLIED PHYSICS LETTERS 99, 122108 (2011)

 

The effect of chemical residues on the physical and electrical properties of chemical vapor deposited graphene transferred to SiO2

A. Pirkle, J. Chan, A. Venugopal, D. Hinojos, C. W. Magnuson, S. McDonnell, L. Colombo, E. M. Vogel, R. S. Ruoff, and R. M. Wallace

The effects of residues introduced during the transfer of chemical vapor deposited graphene from a Cu substrate to an insulating (SiO2) substrate on the physical and electrical of the transferred graphene are studied. X-ray photoelectron spectroscopy and atomic force microscopy show that this residue can be substantially reduced by annealing in vacuum. The impact of the removal of poly(methyl methacrylate) residue on the electrical properties of graphene field effect devices is demonstrated, including a nearly 2´increase in average mobility from 1400 to 2700 cm2/Vs. The electrical results are compared with graphene doping measurements by Raman spectroscopy.

© 2011 American Institute of Physics [DOI: 10.1063/1.3643444]

 

IEEE ELECTRON DEVICE LETTERS, VOL. 32, NO. 7, JULY 2011

Contact Resistance Reduction to FinFET Source/Drain Using Novel Dielectric Dipole Schottky Barrier Height Modulation Method

Brian E. Coss, Casey Smith, Wei-Yip Loh, Prashant Majhi, Robert M. Wallace,  Jiyoung Kim, and Raj Jammy

Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, TX 75080

SEMATECH, Austin, TX 78741 USA

Recent experiments have demonstrated the ability to alleviate Fermi-level pinning, resulting in reduced Schottky barrier heights (SBHs) and reduced contact resistivity by inserting thin layers of dielectric at the contact interface. In this letter, FinFETs with dielectric SBH tuning layers are investigated and shown to have reduced contact resistance over the control wafer. The reduced contact resistivity results in an ≈25% increase in drive current as well as a reduction of RS/D by 100 Ω · μm. Contact chain measurement shows a 10-Ω · μm2 reduction in specific contact resistivity over the control wafer associated with a 100-meV reduction in SBH. Routes to further improvements in device performance are discussed, including key material considerations for dielectric tuning layers.

© 2011 IEEE   DOI: 10.1109/LED.2011.2148091

Applied Surface Science 257 (2011) 8747– 8751

SHORT COMMUNICATION

In situ X-ray photoelectron spectroscopy characterization of Al2O3/GaSb interface evolution

S. McDonnell, D.M. Zhernokletov, A.P. Kirk, J. Kim, R.M. Wallace

Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, TX 75080, USA

GaSb(0 0 1) was treated with (NH4)2Sx and the evolution of the interfacial chemistry was investigated, in situ, with monochromatic X-ray photoelectron spectroscopy (XPS), following heat treatment and exposure to trimethylaluminum (TMA) and deionized water (DIW) in an atomic layer deposition reactor. Elemental Sb (Sb–Sb bonding) as well as Sb3+ and Sb5+ chemical states were initially observed at the native oxide/GaSb interface, yet these diminished below the XPS detection limit after heating to 300 ◦C. No evidence of Ga–Ga bonding was observed whereas the Ga1+/Ga–S chemical state was robust and persisted after heat treatment and exposure to TMA/DIW at 300 ◦C.

© 2011 Elsevier B.V. DOI: 10.1016/j.apsusc.2011.05.034

 

 

APPLIED PHYSICS LETTERS 97, 082901 (2010)

 

The effect of graphite surface condition on the composition of Al2O3 by atomic layer deposition

A. Pirkle, S. McDonnell, B. Lee, J. Kim, L. Colombo, and R. M. Wallace

Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA

Texas Instruments Incorporated, Dallas, Texas 75265, USA

Received 19 July 2010; accepted 23 July 2010; published online 24 August 2010

We present a study of the nucleation of atomic layer deposition of Al2O3 on highly oriented pyrolytic graphite HOPG using trimethlyaluminum (TMA) with ozone as the oxidant (TMA/O3). In situ x-ray photoelectron spectroscopy (XPS) is used to study TMA/O3 depositions on HOPG. We examine the dependence of TMA/O3 nucleation on deposition temperature and characterize the morphology and uniformity of deposited films by ex situ atomic force microscopy. The impact of several predeposition surface treatments of the graphite surface condition is discussed, particularly with regard to the presence of adsorbed atmospheric contamination.

© 2010 American Institute of Physics. [doi:10.1063/1.3479908]

 

APPLIED PHYSICS LETTERS 97, 043107 (2010)

Characteristics of high-k Al2O3 dielectric using ozone-based atomic layer deposition for dual-gated graphene devices

B. Lee,G. Mordi, M. J. Kim,Y. J. Chabal,E. M. Vogel, R. M. Wallace, K. J. Cho, L. Colombo, and J. Kim

Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080, USA

Texas Instruments, Inc., 12500 TI Boulevard Dallas, Texas 75266, USA

(Received 2 October 2009; accepted 1 July 2010; published online 28 July 2010)

We present characteristics of dual-gated graphene devices with an Al2O3 gate dielectric formed by an O3-based atomic-layer-deposition process. Raman spectra reveal that a O3 process at 25 °C on single-layered graphene introduces the least amount defects, while a substantial number of defects appear at 200 °C. This graphene device with O3-based Al2O3 dielectric demonstrates a heterojunction within the graphene sheet when applying VTG and VBG and possesses good dielectric properties with minimal chemical doping, including a high dielectric constant 8, low hysteresis width 0.2 V, and low leakage current and a carrier mobility of 5000 cm2 /V s 25 °C in ambient.

 © 2010 American Institute of Physics. [doi:10.1063/1.3467454]

 

APPLIED PHYSICS LETTERS 97, 143502 (2010)

Fermi level unpinning of GaSb (100) using plasma enhanced atomic layer deposition of Al2O3

A. Ali, H. S. Madan, A. P. Kirk, D. A. Zhao, D. A. Mourey, M. K. Hudait, R. M. Wallace, T. N. Jackson, B. R. Bennett, J. B. Boos, and S. Datta

Penn State University, University Park, Pennsylvania 16802, USA

The University of Texas at Dallas, Richardson, Texas 75080, USA

Virginia Tech, Blacksburg, Virginia 24061, USA

Naval Research Laboratory, Washington, DC 20375, USA

(Received 14 May 2010; accepted 2 September 2010; published online 4 October 2010)

N-type and p-type GaSb metal-oxide-semiconductor capacitors (MOSCAPs) with atomic-layer-deposited (ALD) and plasma-enhanced-ALD (PEALD) Al2O3 dielectrics are studied to identify the optimum surface preparation and oxide deposition conditions for a high quality oxide-semiconductor interface. The ALD Al2O3 /GaSb MOSCAPs exhibit strongly pinned C-V characteristics with high interface state density (Dit) whereas the PEALD Al2O3 /GaSb MOSCAPs show unpinned C-V characteristics low Dit. The reduction in Sb2O3 to metallic Sb is suppressed for the PEALD samples due to lower process temperature, identified by x-ray photoelectron spectroscopy analysis. Absence of elemental Sb is attributed to unpinning of Fermi level at the PEALD Al2O3 /GaSb interface.

 © 2010 American Institute of Physics. [doi:10.1063/1.3492847]

 

Journal of Physical Chemistry C 114, 22610 (2010)

Impact of Interfacial Oxygen Content on Bonding, Stability, Band Offsets, and Interface States of GaAs:HfO2 Interfaces

Weichao Wang, Ka Xiong, Robert M. Wallace, and Kyeongjae Cho

Department of Materials Science & Engineering, and Department of Physics, The University of Texas at Dallas, Richardson, Texas 75252, United States

(Received: August 19, 2010; Revised Manuscript Received: October 6, 2010)

A theoretical study of the structural and electronic properties of GaAs:HfO2 interface is performed using the density functional theory method. For the interfaces with Ga-O bonds (formed between Ga-terminated GaAs surface and O-terminated HfO2 surface), we found that the interfaces with 10% and 20% interfacial oxygen removed are thermodynamically stable over a wide range of O chemical potential. By gradually decreasing the interfacial O content from 100% to 30% (by changing O chemical potential corresponding to varying the growth condition), the valence band offset increases from 1.06 to 3.34 eV. The analysis of the electronic structures indicates that for interfaces with high interfacial oxygen content, the interface gap states are induced by interfacial Ga dangling bonds and As-As dimer pairs, which are formed by interface atomic structure reconstruction. The decreasing interfacial oxygen content causes the decrease of the charge states of interfacial Hf and Ga leading to metallic interface states. For interfaces with low interfacial oxygen content, we found that As-As, Ga-Ga dimer pairs, and Ga and As dangling bonds are also formed and contribute to the interface gap states.

©  2010 American Chemical Society [doi: 10.1021/jp107880r]

 

APPLIED PHYSICS LETTERS 95, 222105 (2009)

Near band edge Schottky barrier height modulation using high-k dielectric dipole tuning mechanism

B. E. Coss, W.-Y. Loh, R. M. Wallace, J. Kim, P. Majhi, and R. Jammy

SEMATECH, 2706 Montopolis Drive, Austin, Texas 78741, USA

University of Texas at Dallas, 800 West Campbell Road, Richardson, Texas 75080, USA

(Received 3 September 2009; accepted 11 October 2009; published online 2 December 2009)

Schottky barrier height tuning using high-k /SiO2 interfacial dipoles is reported. Schottky barrier heights of 1.0 and 0.2 eV are observed in a TaN/p-Si diode by insertion of thin layers of high-k (LaOx ,AlOx) and SiO2 at the metal-semiconductor interface. The dipole tunes the effective work function of TaN/p-Si by more than 0.8 eV to achieve effective Schottky barrier heights near conduction and valence band edge. LaOx (n-type) and AlOx (p-type) have a dipole potential offsets estimated to be 0.3 and 0.5 V, respectively. Applications to lowering contact resistivity are discussed, as well as a comparison of other dipole offsets.

© 2009 American Institute of Physics. [doi:10.1063/1.3263719]

 

APPLIED PHYSICS LETTERS 94, 162101 (2009)

Detection of Ga suboxides and their impact on III-V passivation and Fermi-level pinning

C. L. Hinkle, M. Milojevic, B. Brennan, A. M. Sonnet, F. S. Aguirre-Tostado,

G. J. Hughes, E. M. Vogel, and R. M. Wallace

Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA

Department of Electrical Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA

School of Physical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland

(Received 29 January 2009; accepted 27 March 2009; published online 20 April 2009)

The passivation of interface states remains an important problem for III-V based semiconductor devices. The role of the most stable bound native oxides GaOx (0.5£x£1.5) is of particular interest. Using monochromatic x-ray photoelectron spectroscopy in conjunction with controlled GaAs(100) and InGaAs(100) surfaces, a stable suboxide (Ga2O) bond is detected at the interface but does not appear to be detrimental to device characteristics. In contrast, the removal of the Ga 3+ oxidation state (Ga2O3) is shown to result in the reduction of frequency dispersion in capacitors and greatly improved performance in III-V based devices.

 © 2009 American Institute of Physics. [DOI: 10.1063/1.3120546]

 

APPLIED PHYSICS LETTERS 93, 202902 (2008)

Half-cycle atomic layer deposition reaction studies of Al2O3 on In0.2Ga0.8As (100) surfaces

M. Milojevic, F. S. Aguirre-Tostado, C. L. Hinkle, H. C. Kim, E. M. Vogel, J. Kim, and

R. M. Wallace

Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75083, USA

(Received 16 June 2008; accepted 29 October 2008; published online 19 November 2008)

The reduction in III–V interfacial oxides by atomic layer deposition of Al2O3 on InGaAs is studied by interrupting the deposition following individual trimethyl aluminum (TMA) and water steps (half cycles) and interrogation of the resultant surface reactions using in situ monochromatic x-ray photoelectron spectroscopy (XPS). TMA is found to reduce the interfacial oxides during the initial exposure. Concentrations of Ga oxide on the surface processed at 300 °C are reduced to a concentration on the order of a monolayer, while AsOx species are below the level of detection of XPS.

© 2008 American Institute of Physics. [DOI: 10.1063/1.3033404]

APPLIED PHYSICS LETTERS 93, 122109 (2008)

Performance enhancement of n-channel inversion type InxGa1−xAsmetal-oxide-semiconductor field effect transistor using ex situ deposited thin amorphous silicon layer

A. M. Sonnet, C. L. Hinkle, M. N. Jivani, R. A. Chapman, G. P. Pollack,

R. M. Wallace, and E. M. Vogel

Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA

(Received 22 August 2008; accepted 8 September 2008; published online 26 September 2008)

Significant enhancement in metal-oxide-semiconductor field effect transistor (MOSFET) transport characteristics is achieved with InxGa1−xAs (x=0.53, x=0.20) channel material using ex situ plasma enhanced chemical vapor deposited amorphous Si layer. InxGa1−xAs MOSFETs (L=2 mm, Vgs-Vt =2.0 V) with Si interlayer show a maximum drain current of 290 mA/mm (x=0.53) and 2 mA/mm (x=0.20), which are much higher compared to devices without a Si interlayer. However, charge pumping measurements show a lower average interface state density near the intrinsic Fermi level for devices without the silicon interlayer indicating that a reduction in the midgap interface state density is not responsible for the improved transport characteristics.

© 2008 American Institute of Physics. [DOI: 10.1063/1.2991340]

 

APPLIED PHYSICS LETTERS 92, 203102 2008

Conformal Al2O3 dielectric layer deposited by atomic layer deposition for graphene-based nanoelectronics

Bongki Lee, Seong-Yong Park, Hyun-Chul Kim, KyeongJae Cho, Eric M. Vogel,

Moon J. Kim, Robert M. Wallace, and Jiyoung Kim

Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA

(Received 15 February 2008; accepted 24 April 2008; published online 20 May 2008)

We present a facile route which combines the functionalization of a highly oriented pyrolytic graphite surface with an atomic layer deposition (ALD) process to allow for conformal Al2O3 layers. While the trimethylaluminum  TMA /H2O process caused selective deposition only along step edges, the TMA/O3 process began to provide nucleation sites on the basal planes of the surface. O3 pretreatment, immediately followed by the ALD process with TMA/O3 chemistry, formed Al2O3 layers without any preferential deposition at the step edges. This is attributed to functionalization of graphene by ozone treatment, imparting a hydrophilic character which is desirable for ALD deposition.

 © 2008 American Institute of Physics. [DOI: 10.1063/1.2928228]

APPLIED PHYSICS LETTERS 92, 171906 (2008)

Indium stability on InGaAs during atomic H surface cleaning

F. S. Aguirre-Tostado,M. Milojevic, C. L. Hinkle, E. M. Vogel, and R. M. Wallace

Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA

S. McDonnell  and G. J. Hughes

School of Physical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland

(Received 29 February 2008; accepted 8 April 2008; published online 30 April 2008)

Atomic H exposure of a GaAs surface at 390 °C is a relatively simple method for removing the native oxides without altering the surface stoichiometry. In-situ reflection high energy electron diffraction and angle-resolved x-ray photoelectron spectroscopy have been used to show that this procedure applied to In0.2Ga0.8As effectively removes the native oxides resulting in an atomically clean surface. However, the bulk InGaAs stoichiometry is not preserved from this treatment. The In:Ga ratio from the substrate is found to decrease by 33%. The implications for high-mobility channel applications are discussed as the carrier mobility increases nearly linearly with the In content.

 © 2008 American Institute of Physics. [DOI: 10.1063/1.2919047]

 

 

APPLIED PHYSICS LETTERS 92, 071901 (2008)

GaAs interfacial self-cleaning by atomic layer deposition

C. L. Hinkle, A. M. Sonnet, E. M. Vogel, M. Milojevic, B. Lee, F. S. Aguirre-Tostado, K. J. Choi, H. C. Kim, J. Kim, and R. M. Wallace

Department of  Materials Science and Engineering,, The University of Texas at Dallas, Richardson, Texas 75080, USA

S. McDonnell and G. J. Hughes

School of Physical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland

(Received 14 January 2008; accepted 29 January 2008; published online 19 February 2008)

The reduction and removal of surface oxides from GaAs substrates by atomic layer deposition (ALD) of Al2O3 and HfO2 are studied using in situ monochromatic x-ray photoelectron spectroscopy. Using the combination of in situ deposition and analysis techniques, the interfacial "self-cleaning" is shown to be oxidation state dependent as well as metal organic precursor dependent. Thermodynamics, charge balance, and oxygen coordination drive the removal of certain species of surface oxides while allowing others to remain. These factors suggest proper selection of surface treatments and ALD precursors can result in selective interfacial bonding arrangements.

© 2008 American Institute of Physics. [DOI: 10.1063/1.2883956]

APPLIED PHYSICS LETTERS 91, 142122 (2007)

Interface studies of GaAs metal-oxide-semiconductor structures using atomic-layer-deposited HfO2/Al2O3 nanolaminate gate dielectric

T. Yang, Y. Xuan, D. Zemlyanov, T. Shen, Y. Q. Wu, J. M. Woodall, and P. D. Yea

School of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA

F. S. Aguirre-Tostado, M. Milojevic, S. McDonnell, and R. M. Wallace

Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75083, USA

(Received 1 August 2007; accepted 21 September 2007; published online 5 October 2007)

A systematic capacitance-voltage study has been performed on GaAs metal-oxide-semiconductor (MOS) structures with atomic-layer-deposited HfO2/Al2O3 nanolaminates as gate dielectrics. A HfO2/Al2O3 nanolaminate gate dielectric improves the GaAs MOS characteristics such as dielectric constant, breakdown voltage, and frequency dispersion. A possible origin for the widely observed larger frequency dispersion on n-type GaAs than p-type GaAs is discussed. Further experiments show that the observed hysteresis is mainly from the mobile changes and traps induced by HfO2 in bulk oxide instead of those at oxide/GaAs interface. © 2007 American Institute of Physics.

[DOI: 10.1063/1.2798499]

APPLIED PHYSICS LETTERS 91, 163512 (2007)

Frequency dispersion reduction and bond conversion on n-type GaAs by in situ surface oxide removal and passivation

C. L. Hinkle, A. M. Sonnet, and E. M. Vogel

Department of Electrical Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA

S. McDonnell and G. J. Hughes

School of Physical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland

M. Milojevic, B. Lee, F. S. Aguirre-Tostado, K. J. Choi, J. Kim, and R. M. Wallace

Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA

(Received 4 September 2007; accepted 2 October 2007; published online 19 October 2007)

The method of surface preparation on n-type GaAs, even with the presence of an amorphous-Si interfacial passivation layer, is shown to be a critical step in the removal of accumulation capacitance frequency dispersion. In situ deposition and analysis techniques were used to study different surface preparations, including NH4OH, Si-flux, and atomic hydrogen exposures, as well as Si passivation depositions prior to in situ atomic layer deposition of Al2O3. As–O bonding was removed and a bond conversion process with Si deposition is observed. The accumulation capacitance frequency dispersion was removed only when a Si interlayer and a specific surface clean were combined.

© 2007 American Institute of Physics. [DOI: 10.1063/1.2801512]

 

 

JOURNAL OF APPLIED PHYSICS 102, 024112 (2007)

Oxygen species in HfO2 films: An in situ x-ray photoelectron spectroscopy study

C. Driemeier

Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre 91501-970, Brazil

and University of Texas at Dallas, Richardson, Texas 75080, USA

R. M. Wallace

Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080, USA

I. J. R. Baumvol

CCET, Universidade de Caxias do Sul, Caxias do Sul 95070-560, Brazil and Instituto de Física,

Universidade Federal do Rio Grande do Sul, Porto Alegre 91501-970, Brazil

(Received 30 April 2007; accepted 13 June 2007; published online 25 July 2007)

The chemical bonding of O atoms in HfO2 films on Si was investigated by in situ x-ray photoelectron spectroscopy in the O 1s spectral region. In addition to trivial O forming only O-Hf bonds, O 1s signals corresponding to nontrivial secondary O  Osec were also observed. By ruling out possible roles of impurities as well as by comparing O 1s signals for different thermochemical processing routes, Osec chemical origins were inferred. Moreover, angle-resolved photoelectron analysis was employed to quantitatively separate surface and bulk Osec contributions. Surface Osec was assigned to surface O-H groups generated either by room temperature water vapor exposure or by 600 °C H2 annealing. Bulk Osec was assigned to O-O or O-H bonds and, as indicated by thermodynamic calculations and complementary structural analysis, is located in HfO2 amorphous regions and grain boundaries. This bulk Osec can be partly removed by annealing in reducing atmospheres. For some of the processing routes employed here, we observed additional, water-induced bulk Osec, which was attributed to dissociative water absorption in HfO2 amorphous regions and O-depleted grain boundaries. © 2007 American Institute of Physics.

[DOI: 10.1063/1.2759198]

 

 

APPLIED PHYSICS LETTERS 90, 262105 (2007)

14 MHz organic diodes fabricated using photolithographic processes

Yuming Ai, Srinivas Gowrisanker, Huiping Jia, Isaac Trachtenberg, Eric Vogel,

Robert M. Wallace, Bruce E. Gnade, Raymond Barnett, Harvey Stiegler, and Hal Edwards

Materials Science and Engineering, Erik Jonsson School of Engineering and Computer Science, University of Texas at Dallas, Richardson, Texas 75083

(Received 1 April 2007; accepted 5 June 2007; published online 26 June 2007)

Organic semiconductor-based Schottky diodes operating at 14 MHz, fabricated using conventional photolithographic and etching processes, have been demonstrated. Copper phthalocyanine is the semiconductor, with gold and aluminum as the Ohmic and Schottky contacts, respectively. The organic diode based rectifier circuit generated a dc output voltage of approximately 2 V at 14 MHz,  using an input ac signal with a zero-to-peak voltage amplitude of 5 V. These devices showed little degradation under continuous ac voltage stress when operated in vacuum.

© 2007 American Institute of Physics. [DOI: 10.1063/1.2752533]

 

 

APPLIED PHYSICS LETTERS 89, 032904 (2006)

Comparison of electrical and chemical characteristics of ultrathin HfON versus HfSiON dielectrics

G. Pant, A. Gnade, M. J. Kim, R. M. Wallace, and B. E. Gnade

Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080

M. A. Quevedo-Lopez, P. D. Kirsch, and S. Krishnan

SEMATECH, 2706 Montopolis Drive, Austin, Texas 78741

(Received 30 January 2006; accepted 25 May 2006; published online 19 July 2006)

The electrical and chemical properties of ultrathin HfON and HfSiON gate dielectrics are investigated as a function of physical thickness. Grazing incidence x-ray diffraction was used to detect phase separation and crystallization of 1.5, 2.0, 2.5, and 4.0 nm films of HfON and HfSiON after a 1000 °C-10 s activation annealing. X-ray photoelectron spectroscopy was used to determine the chemical composition of the dielectrics. No evidence of crystallization was detected in 1.5 nm HfON or HfSiON films after the activation annealing. The HfON film showed crystallization at a 2.0 nm thickness whereas the 2.0 nm HfSiON film remained amorphous.

 © 2006 American Institute of Physics. [DOI: 10.1063/1.222699]

 

APPLIED PHYSICS LETTERS 88, 072108 (2006)

Composition dependence of the work function of Ta1-xAlxNy metal gates

H. N. Alshareef, K. Choi, H. C. Wen, H. Luan, H. Harris, Y. Senzaki, P. Majhi, B. H. Lee, and R. Jammy

SEMATECH, 2706 Montopolis Drive, Austin, Texas 78741

S. Aguirre-Tostado, B. E. Gnade, and R. M. Wallace

Department of Electrical Engineering, University of Texas at Dallas, Richardson, Texas 75080

(Received 3 October 2005; accepted 23 January 2006; published online 16 February 2006)

It is shown that the work function of Ta1-xAlxNy depends on the electrode and gate dielectric compositions. Specifically, the work function of Ta1-xAlxNy increased with SiO2 content in the gate dielectric, reaching as high as 5.0 eV on SiO2; the work function was nearly 400 mV smaller on HfO2. In addition, the work function decreased with increasing nitrogen content in the Ta1-xAlxNy metal gate. Increasing Al concentration increased the work function up to about 15% Al, but the work function decreased for higher Al concentrations. Chemical analysis shows that Al–O bonding at the interface correlates with the observed work function values.

© 2006 American Institute of Physics. [DOI: 10.1063/1.2174836]

 

APPLIED PHYSICS LETTERS 88, 041918 (2006)

Interaction of HfO2 /SiO2 /Si structures with deuterium gas

C. Driemeier and L. Miotti
Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre 91501-970, Brazil

I. J. R. Baumvol
CCET, Universidade de Caxias do Sul and Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre 91501-970, Brazil

C. Radtke
Pós-Graduação em Microeletrônica, Universidade Federal do Rio Grande do Sul, Porto Alegre 91501-970, Brazil

E. P. Gusev
IBM Research Division, T. J. Watson Research Center P.O. Box 218, Yorktown Heights, New York 10598

M. J. Kim and R. M. Wallace
Department of Electrical Engineering and Physics, University of Texas at Dallas, Richardson, Texas 75080

(Received 29 August 2005; accepted 7 December 2005; published online 27 January 2006)

HfO2 films (2.5 to 12 nm) deposited on thermal SiO2 (1.5 nm) on Si were annealed in deuterium gas at 400–600 °C and incorporated D amounts were quantified using the D(3He, p)4He nuclear reaction. We found ~1013 D cm-2 in the SiO2 interlayer region and up to 2.2x1014 D cm-2 near the HfO2 surface, whereas D amounts in the bulk of the HfO2 films were determined to be below 1013 cm-2. However, analyses employing the 1H(15N, ag)12C nuclear resonant reaction showed much more spurious H present in the bulk of HfO2 films. Mechanisms of D incorporation and desorption as well as contribution of the present results to the understanding of HfO2-based devices are discussed.

 © 2006 American Institute of Physics. [DOI: 10.1063/1.216850]

APPLIED PHYSICS LETTERS 88, 032901 (2006)

Effect of thickness on the crystallization of ultrathin HfSiON gate dielectrics

G. Pant, A. Gnade, M. J. Kim, R. M. Wallace, and B. E. Gnade

Department of Electrical Engineering, University of Texas at Dallas, Richardson, Texas 75080

M. A. Quevedo-Lopez and P. D. Kirsch

SEMATECH, 2706 Montopolis Drive, Austin, Texas 78741

(Received 19 September 2005; accepted 25 November 2005; published online 17 January 2006)

The crystallization of ultrathin hafnium silicon oxynitride (HfSiON) gate dielectric is studied as a function of physical thickness. Grazing incidence x-ray diffraction (GI-XRD) was used to detect phase separation and crystallization of 1.5, 2.0, 2.5, and 4.0 nm HfSiON films after 1000 °C 10 s dopant activation anneal. Crystallization peaks corresponding to monoclinic and tetragonal HfO2 were detected in 2.5 and 4.0 nm HfSiON films. These GI-XRD results were supported by plan-view transmission electron microscopy images of the HfSiON films. Film crystallinity seems to impact voltage instability in thicker HfSiON films.

 © 2006 American Institute of Physics. [DOI: 10.1063/1.2165182]

APPLIED PHYSICS LETTERS 88, 112907 (2006)

Electrical characterization of amorphous lanthanum aluminate thin films grown by molecular-beam deposition on silicon

L. F. Edge and D. G. Schlom

Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802-5005

P. Sivasubramani and R. M. Wallace

Departments of Electrical Engineering and Physics, University of Texas at Dallas, Richardson, Texas 75080

B. Holländer and J. Schubert

Institut für Schichten und Grenzflächen ISG1-IT, Forschungszentrum Jülich GmbH, D-52425 Jülich Germany

(Received 28 November 2005; accepted 9 February 2006; published online 16 March 2006)

Amorphous LaAlO3 thin films were deposited at room temperature directly on n-type and p-type Si 001 by molecular beam deposition. The dielectric properties of the stoichiometric amorphous LaAlO3 thin films deposited on silicon were determined through capacitance-voltage and current-voltage measurements. The electrical measurements indicate that the amorphous LaAlO3 thin films have a dielectric constant (K) of K=16±2. This is significantly lower than the K=24 of crystalline LaAlO3. The equivalent oxide thickness values range between 9.8 and 15.5 Å for films deposited on n-type silicon with physical thicknesses of 45–75 Å.

© 2006 American Institute of Physics. [DOI: 10.1063/1.2182019]

 

APPLIED PHYSICS LETTERS 87, 262902 (2005)

Ultrascaled hafnium silicon oxynitride gate dielectrics with excellent carrier mobility and reliability

M. A. Quevedo-Lopez

Texas Instruments assignee at SEMATECH, 2706 Montopolis Drive, Austin, Texas 78741-6499

S. A. Krishnan and P. D. Kirsch

SEMATECH, 2706 Montopolis Drive, Austin, Texas 78741-6499

G. Pant, B. E. Gnade, and R. M. Wallace

Department of Electrical Engineering, University of Texas at Dallas, Richardson, Texas 75080

(Received 1 August 2005; accepted 27 October 2005; published online 19 December 2005)

A hafnium silicon oxynitride gate dielectric with a universal channel mobility of ~90% at 1 MV/cm, equivalent oxide thickness of approximately 1 nm, and leakage current 200´ less than SiO2 is reported. X-ray photoelectron spectroscopy results suggest that the small peak mobility loss observed in scaled HfSiON may be attributed to increased Si–N bonding near the silicon interface. In accordance with these mobility results, the Si–N:Hf–N bond ratio decreases with increasing HfSiON physical thickness. Threshold voltage instability at 1 nm equivalent oxide thickness is less than 10 mV after a 1000 s stress at 22 MV/cm. DVTH monotonically increases with HfSiON physical thickness. This is associated with greater crystallization in thicker HfSiON films.

© 2005 American Institute of Physics. [DOI: 10.1063/1.215058]

 

 

 

APPLIED PHYSICS LETTERS 86, 201901 (2005)

Outdiffusion of La and Al from amorphous LaAlO3 in direct contact

with Si (001)

 

P. Sivasubramani, M. J. Kim, B. E. Gnade, and R. M. Wallace

Department of Electrical Engineering and Physics, University of Texas at Dallas, Richardson, Texas 75080

 

L. F. Edge and D. G. Schlom

Department of Materials Science and Engineering, Pennsylvania State University, University Park,

Pennsylvania 16802

 

H. S. Craft and J.-P. Maria

Department of Materials Science and Engineering, North Carolina State University, Raleigh,

North Carolina 27606

(Received 26 January 2005; accepted 19 April 2005; published online 9 May 2005)

We have evaluated the thermal stability of Al2O3/LaAlO3/Si (001) stacks with atomic force microscopy, x-ray diffraction, transmission electron microscopy, and secondary ion mass spectrometry using a back side polishing approach. Crystallization of the amorphous LaAlO3 film was found to occur for rapid thermal anneals (RTA) above 935 °C for 20 s, in flowing N2. Penetration of Al and La into the underlying Si (001) is clearly observed for RTA at or above 950 °C for 20 s in flowing N2.

 

© 2005 American Institute of Physics. [DOI: 10.1063/1.1928316]

 

 

http://dx.doi.org/10.1063/1.1928316

JOURNAL OF APPLIED PHYSICS 97, 043508 (2005)

Dopant penetration studies through Hf silicate

M. A. Quevedo-Lopez

Department of Materials Science and Engineering, University of North Texas, Denton, Texas

 

M. R. Visokay, J. J. Chambers, M. J. Bevan, A. LiFatou, and L. Colombo

Silicon Technology Development, Texas Instruments, Inc., Dallas, Texas

 

M. J. Kim, B. E. Gnade, and R. M. Wallace

Department of Electrical Engineering University of Texas at Dallas, Richardson, Texas

 

(Received 4 December 2003; accepted 17 November 2004; published online 21 January 2005)

 

We present a study of the penetration of B, P, and As through Hf silicate (HfSixOy) and the effect of N incorporation in Hf silicate (HfSixOyNz) on dopant penetration from doped polycrystalline silicon capping layers. The extent of penetration through Hf silicate was found to be dependent upon the thermal annealing budget for each dopant investigated as follows: B (T³950 °C/60 s),  P (T³1000 °C/20 s), and As (T³1050 °C/60 s). We propose that the enhanced diffusion observed for these dopants in HfSixOy, compared with that of SiO2 films, is related to grain boundary formation resulting from HfSixOy film crystallization. We also find that, as in the case of SiO2, N incorporation inhibits dopant (B, P, and As) diffusion through the Hf silicate and thus penetration into the underlying Si substrate. Only B penetration is clearly observed through HfSiON films for anneals at 1050 °C for durations of 10 s or longer. The calculated B diffusivity through the HfSixOyNz layer is D0=5.23×10-15 cm2/s.

 

© 2005 American Institute of Physics. [DOI: 10.1063/1.1846138]

 

http://dx.doi.org/10.1063/1.1846138

 

Appl. Phys. A 80, 1045–1047 (2005)

 

Atomic transport and chemical stability

of nitrogen in ultrathin HfSiON gate dielectrics

 

C. Driemeier, K.P. Bastos, G.V. Soares, L. Miotti, R.P. Pezzi,

Instituto de F sica – UFRGS, CP 15051 Porto Alegre 91501-970 Brazil

 

I.J.R. Baumvol

Centro de Ciências Exatas e Tecnol´ogicas – UCS, 95070-560 Caxias do Sul Brazil

 

P. Punchaipetch, G. Pant, B.E. Gnade, R.M. Wallace

Department of Electrical Engineering, University of Texas at Dallas, Richardson, TX 75083, USA

Received: 2 August 2004/Accepted: 19 August 2004

Published online: 30 September 2004 • © Springer-Verlag 2004

ABSTRACT HfSiO and HfSiON films with thicknesses compatible with the requirements for gate dielectrics alternatives to SiO2 in ultra-large scale integration silicon-based CMOSFET devices were deposited on an ultrathin HfSiO15N interfacial layer on Si(001). These structures were submitted to thermal processing routines typical of post-deposition annealing and dopant activation steps in fabrication technology, namely at 450 or 1000 .C, respectively, and in atmospheres ofN2 and/orO2. N transport and loss were determined by nuclear reaction analysis, including sub-nanometric depth resolution profiling with narrow nuclear reaction resonances. The chemical states of N were accessed by angle-resolved X-ray photoelectron spectroscopy.

After annealing at 450 .C, N is seen to be mobile, whereas the chemical environment of N is not changed at this temperature. Annealing at 1000 .C renders N mobile and its most abundant chemical state in near-surface regions is unstable. Annealing in O2 atmosphere promotes incorporation of O from the gas phase into the films, partly in exchange for N and O atoms and partly by net incorporation of oxygen in the films. The profiles of the newly incorporated O atoms are also determined with sub-nanometric depth resolution by narrow nuclear reaction resonance profiling.

PACS 68.60.-p; 68.55.-a; 73.61.Ng; 73.40.Qv

[DOI: 10.1007/s00339-004-3037-8]

 

Hydrogen and deuterium incorporation and transport in hafnium-based dielectric films on silicon

R. P. Pezzi, L. Miotti, K. P. Bastos, G. V. Soares, and C. Driemeier

Instituto de Física, UFRGS, Av. Bento Gonçalves, 9500, Porto Alegre, RS, Brazil 91509-900

 

I. J. R. Baumvol

Centro de Ciências Exatas e Tecnológicas, UCS, Caxias do Sul, RS, Brazil 95070-560

 

P. Punchaipetch, G. Pant, B. E. Gnade, and R. M. Wallace

Department of Electrical Engineering, University of Texas at Dallas, Richardson, Texas 75083

 

A. Rotondaro, J. M. Visokay, J. J. Chambers, and L. Colombo

Silicon Technology Development, Texas Instruments Incorporated, Dallas, Texas

 

(Received 24 March 2004; accepted 11 August 2004)

 

Hydrogen and deuterium incorporation into nitrided and non-nitrided hafnium silicate films on Si during thermal annealing in 1H- and 2H-containing atmospheres was investigated. 1H profiling was accessed by means of nuclear resonant reaction profiling, whereas 2H incorporation was quantified by nuclear reaction analysis. The effects of preannealing in different atmospheres and temperatures were determined, as well as the losses of 1H and 2H from these structures during postannealing in vacuum. The results reveal a rather uniform depth distribution of incorporated 1H, in striking contrast with previous studies on hydrogen in silicon oxide and oxynitrides and hafnium oxide films on Si. These results are discussed in terms of the defects present in each one of the structures studied here.

 

© 2004 American Institute of Physics.

[DOI: 10.1063/1.1801682]

http://dx.doi.org/10.1063/1.1801682

 

J. Vac. Sci. Technol. A 22(2), Mar/Apr 2004

 

Growth and characterization of hafnium silicate films prepared

by UV/ozone oxidation

 

Prakaipetch Punchaipetch, Gaurang Pant, M. J. Kim, Robert M. Wallace, and Bruce E. Gnade

Department of Electrical Engineering, University of Texas, Dallas, Richardson, Texas 75083

 

(Received 14 July 2003; accepted 29 December 2003; published 17 February 2004)

 

Physical and electrical properties of hafnium silicate (HfSixOy) dielectric films prepared by room-temperature UV/ozone (O3) oxidation of hafnium silicide (HfSi2) are reported. Angle-resolved x-ray photoelectron spectroscopy was used to determine chemical bonding at the film interface and within the bulk film. These films, with 12 at.% Hf composition, have a dielectric constant  (k) of ~8–9 and exhibit a flat-band voltage shift of 60 mV. The leakage current density at VFB + 1 V is 4.7×10-5 A/cm2 for a 4.7-nm-thick film (capacitance equivalent thickness =2.6 nm) and breakdown strength was >8 MV/cm.

 

 © 2004 American Vacuum Society.

[DOI: 10.1116/1.1649346]

 

 

Research