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Search Publications by: David Gundlach (Fed)

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Displaying 26 - 50 of 91

Influence of Metal?MoS2 Interface on MoS2 Transistor Performance: Comparison of Ag and Ti Contacts

December 16, 2014
Author(s)
Hui H. Yuan, Guangjun Cheng, Lin You, Haitao Li, Hao Zhu, Wei Li, Joseph J. Kopanski, Yaw S. Obeng, Angela R. Hight Walker, David J. Gundlach, Curt A. Richter, D. E. Ioannou, Qiliang Li
In this work, we present a study of enhancing MoS2 transistor performance by using proper metal contact. We found that the on-state current of MoS2 field-effect transistors with 30 nm Au/ 30 nm Ag contacts is enhanced more than 60 times and the

Electron and Hole Photoemission Detection for Band Offset Determination of Tunnel Field-Effect Transistor Heterojunctions

November 24, 2014
Author(s)
Wei Li, Qin Zhang, R. Bijesh, Oleg A. Kirillov, Yiran Liang, Igor Levin, Lianmao Peng, Xuelei Liang, S. Datta, David J. Gundlach, Nhan V. Nguyen
The electrical performance of a tunnel field-effect transistor depends critically on the band offset at their semiconductor heterojunction interface. Historically, it has been difficult to experimentally determine how the electronic bands align at the

Interface Engineering to Control Magnetic Field Effects of Organic-Based Devices by Using a Molecular Self-Assembled Monolayer

June 26, 2014
Author(s)
Hyuk-Jae Jang, Sujitra J. Pookpanratana, Alyssa N. Brigeman, Regis J. Kline, James I. Basham, David J. Gundlach, Christina A. Hacker, Oleg A. Kirillov, Oana Jurchescu, Curt A. Richter
Organic semiconductors hold immense promise for the development of a wide range of innovative devices with their excellent electronic and manufacturing characteristics. Of particular interest are non-magnetic organic semiconductors that show unusual

Morphological origin of charge transport anisotropy in aligned polythiophene thin films

June 11, 2014
Author(s)
Brendan T. O'Connor, Obadiah G. Reid, Xinran Zhang, Regis J. Kline, Lee J. Richter, David J. Gundlach, Dean DeLongchamp, Michael F. Toney, Nikos Kopidakis, Garry Rumbles
The morphological origin of anisotropic charge transport in uniaxially strain aligned poly(3-hexylthiophene) (P3HT) films is investigated. The macroscale field effect mobility anisotropy is measured in an organic thin film transistor (OTFT) configuration

Predicting the J-V Curve in Organic Photovoltaics Using Impedance Spectroscopy

June 2, 2014
Author(s)
James I. Basham, Thomas N. Jackson, David J. Gundlach
We employ impedance spectroscopy as a method to predict the current-voltage curve in organic photovoltaics. This technique allows the quantification of the recombination rate, series resistance, carrier density and lifetime very close to normal operating

Highly reproducible and reliable metal/graphene contact by UV-Ozone treatment

March 17, 2014
Author(s)
Wei Li, Christina A. Hacker, Guangjun Cheng, Angela R. Hight Walker, Curt A. Richter, David J. Gundlach, Yiran Liang, boyuan Tian, Xuelei Liang, Lianmao Peng
Resist residue from the device fabrication process is a significant source of contamination at the metal/graphene contact interface. Ultraviolet Ozone (UVO) treatment is proven here, by X-ray photoelectron spectroscopy (XPS) and Raman measurement, to be an

Modulated photocurrent spectroscopy of CdTe/CdS solar cells-equivalent circuit analysis

May 20, 2013
Author(s)
Behrang H. Hamadani, John F. Roller, Kounavis Panagiotis, Nikolai B. Zhitenev, David J. Gundlach
We have used the technique of photocurrent modulated spectroscopy to investigate the dynamic response of charge carrier transport in thin film CdTe/CdS solar cells as a function of light bias and temperature over a broad excitation frequency range. The

Graphene as Transparent Electrode for Direct Observation of Hole Photoemission from Silicon to Oxide

March 27, 2013
Author(s)
Rusen Yan, Qin Zhang, Oleg A. Kirillov, Wei Li, James I. Basham, Alexander G. Boosalis, Xuelei X. Liang, Debdeep Jena, Curt A. Richter, Alan C. Seabaugh, David J. Gundlach, Huili G. Xing, Nhan V. Nguyen
The outstanding electrical and optical properties of graphene make it an excellent alternative as a transparent electrode. Here we demonstrate the application of graphene as collector material in internal photoemission (IPE) spectroscopy; enabling the

Band Offset Determination of Atomic-Layer-Deposited Al2O3 and HfO2 on InP by Internal Photoemission and Spectroscopic Ellipsometry

January 9, 2013
Author(s)
Kun Xu, Oleg A. Kirillov, David J. Gundlach, Nhan V. Nguyen, Pei D. Ye, Min Xu, Lin Dong, Hong Sio
Band offsets at the interfaces of n- and p-type InP ((100) and (111)A) and atomic-layer-deposited (ALD) Al2O3 were measured with internal photoemission and spectroscopic ellipsometry. Similarly, the band offsets at the interface of semi-insulating InP (100

A Unique Photoemission Method to Measure Semiconductor Heterojunction Band Offsets

January 2, 2013
Author(s)
Qin Zhang, Rui Li, Rusen Yan, Thomas Kosel, Grace Xing, Alan Seabaugh, Kun Xu, Oleg A. Kirillov, David J. Gundlach, Curt A. Richter, Nhan V. Nguyen
We report a unique way to measure the energy band offset of a heterojunction by exploiting the light absorption profile in the heterojunction under visible-ultraviolet internal photoemission. This method was used to successfully determine the band

Direct Measurement of Intrinsic Dirac Point and Fermi level at Graphene/Oxide interface and Its Band Alignment by Cavity Enhanced Internal Photoemission

December 17, 2012
Author(s)
Kun Xu, Caifu Zeng, Qin Zhang, Rusen Yan, Peide Ye, Kang Wang, Alan C. Seabaugh, Huili G. Xing, John S. Suehle, Curt A. Richter, David J. Gundlach, Nhan V. Nguyen
We report the first direct measurement of the Dirac point, the Fermi level, and the work function of graphene by performing internal photoemission measurements on a graphene/SiO2/Si structure with a unique optical-cavity enhanced test structure. A complete

Observation of spin-valve effect in Alq3 using a low work function metal

September 7, 2012
Author(s)
Hyuk-Jae Jang, Kurt Pernstich, David J. Gundlach, Oana Jurchescu, Curt A. Richter
We present the observation of magnetoresistance in Co/Ca/Alq3/Ca/NiFe spin-valve devices. Thin Ca layers contacting 150 nm thick Alq3 enable the injection of spin-polarized electrons into Alq3 due to engineering of the band alignment. The devices exhibit

Determination of graphene work function and graphene-insulator-semiconductor band alignment by internal photoemission spectroscopy

July 11, 2012
Author(s)
Rusen Yan, Qin Zhang, Wei Li, Irene G. Calizo, Tian T. Shen, Curt A. Richter, Angela R. Hight Walker, Xuelei X. Liang, David J. Gundlach, Nhan Van Nguyen, Huili G. Xing, Alan Seabaugh
We determined the band alignment of a graphene-oxide-silicon structure using internal photoemission spectroscopy. From the flatband voltage and Dirac voltage we infer a 4.3  10e11 cm-2 negative extrinsic charge present on the graphene surface. Also, we

Measuring domain sizes and compositional heterogeneities in P3HT-PCBM bulk heterojunction thin films with 1H spin diffusion NMR spectroscopy

March 21, 2012
Author(s)
Ryan C. Nieuwendaal, Hyun Wook Ro, David Germack, Regis J. Kline, Calvin Chan, Amit K. Agrawal, David J. Gundlach, David L. VanderHart, Dean M. DeLongchamp
In this manuscript we show that 1H spin diffusion NMR is a valuable method for estimating the domain sizes in thin films of a polymer-fullerene blend for bulk heterojunction (BHJ) photovoltaics. Variations in common BHJ film processing parameters have

Controlling the Microstructure of Solution-Processible Small Molecules in Thin-Film Transistors through Substrate Chemistry

February 4, 2011
Author(s)
Regis J. Kline, Steven D. Hudson, Xinran Zhang, David J. Gundlach, Andrew Moad, Lee J. Richter, Oana Jurchescu, Thomas Jackson, Sanker Subramanian, John E. Anthony, Michael F. Toney
Solution-processible small molecules have tremendous potential for providing both high charge carrier mobility and low cost processing. This study outlines a detailed microstructural study of the effect of substrate chemistry on fluorinated 5,11-bis

Mapping Crystal Orientation in High Performance Thienothiophene Copolymer Thin Films

December 8, 2010
Author(s)
Xinran Zhang, Steven D. Hudson, Dean M. DeLongchamp, David J. Gundlach, Martin Heeney, Iain McCulloch
Mapping of crystalline grain orientation for solution-processed semiconducting polymer thin films is key to understanding charge transport in electronic devices based on them and yet challenging. In this work, a high mobility thienothiophene copolymer

Characterization of a Soluble Anthradithiophene Derivative

October 1, 2010
Author(s)
Brad Conrad, Calvin Chan, Marsha A. Loth, Sean R. Parkin, Xinran Zhang, John E. Anthony, David J. Gundlach
The structural and electrical properties of a new solution processable material, 2,8-diflouro-5,11-tert-butyldimethylsilylethynl anthradithiophene (TBDMS), were measured for single crystal and spun cast thin-film transistors. TBDMS is observed to readily

Why Contacts Matter

July 7, 2010
Author(s)
David J. Gundlach, Y. Li, D. A. Zhou, D A. Mourey, Thomas Jackson