Bulletin of the American Physical Society
2005 72nd Annual Meeting of the Southeastern Section of the APS
Thursday–Saturday, November 10–12, 2005; Gainesville, FL
Session EB: Condensed Matter III: Materials Science |
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Chair: Selman Hershfield, University of Florida Room: Hilton Hawthorne |
Thursday, November 10, 2005 4:15PM - 4:27PM |
EB.00001: Hydrogen-Selective Sensing at Room Temperature with Pt-Coated ZnO Nanorods Hung-Ta Wang, Byoung Sam Kang, Fan Ren, Li-Chia Tien, Patrick Sadik, David Norton, Stephen Pearton, Jenshen Lin The sensitivity for detecting hydrogen with multiple ZnO nanorods is found to be greatly enhanced by sputter-depositing clusters of Pt on the surface. The resulting structures show a change in room temperature resistance upon exposure to hydrogen concentrations in nitrogen of 10-500 ppm approximately a factor of 10 larger than without Pt. Pt-coated ZnO nanorods detected hydrogen down to 10 ppm, with relative responses larger than 0.026 at 10 ppm and larger than 0.085 at 500 ppm hydrogen in nitrogen after 10 min exposure. There was no response at room temperature to oxygen. Approximately 0.95 of the initial ZnO conductance after exposure to hydrogen was recovered within 20s by exposing the nanorods to either air or pure oxygen. This rapid and easy recoverability make the Pt-coated nanorods suitable for practical applications in hydrogen-selective sensing at ppm levels at room temperature with the power consumption less than 0.3 mW. [Preview Abstract] |
Thursday, November 10, 2005 4:27PM - 4:39PM |
EB.00002: Si-Diffused Enhancement-Mode GaN MOSFET Soohwan Jang, Fan Ren, Stephen Pearton, Brent Gila, Mark Hlad, Cammy Abernathy, Hyucksoo Yang, Sang Youn Han, Ching-Jen Pan, Jenn-Inn Chyi Gallium Nitride (GaN) field effect transistors (FETs) have attracted considerable interest as high power electronics for use in the electric utility industry, defense and space applications, and hybrid vehicles. There were some demonstrations of enhancement mode GaN based MOSFETs, however the device performance was poor due to the low channel mobility caused by high temperature (1100-1200 °C) activation annealing after Si implantation. Si implantation was used to form the source and drain region in the GaN MOSFET fabrication. For the alternative method of Si implantation\textbf{, }Si diffusion into GaN was studied as a function of encapsulant type (SiO$_{2}$ or SiN$_{X})$ and diffusion temperature. Using a SiO$_{2}$ encapsulant,the Si diffusion exhibited an activation energy of 0.57 eV with a prefactor of 2.07x10$^{-4 }$ cm$^{2}$.sec$^{-1}$ in the temperature range 800-1000°C. An enhancement mode MgO/GaN-on-Si metal-oxide semiconductor field effect transistor (MOSFET) was fabricated utilizing Si$^{ }$diffused regions under the source and drain to provide an accumulated channel. The devices showed improved transconductance and drain current relative to previous devices with Si-implanted source/drain regions. [Preview Abstract] |
Thursday, November 10, 2005 4:39PM - 4:51PM |
EB.00003: Optimization of Chemical Bath Deposited CdS Thin Films Using Two Different Cadmium Sources Hani Khallaf, Isaiah Oladeji, Lee Chow Owing to its transparency, photoconductivity, and high electron affinity, CdS is known to be the best transparent conducting semiconductor for thin film II-VI compound heterojunction solar cells. In this work, a new method to optimize the deposition of CdS using chemical bath deposition technique is presented. CdSO$_{4}$, and CdCl$_{2}$ have been used as two different Cd sources. NTA (Nitrilotriacetic acid) in addition to KOH have been used as Ligand. Thiourea has been used as the sulfur source. The effect of changing the KOH and NTA concentrations on the film thickness, transmission, and energy gap has been studied. The results were used to develop a set of experiments that include the optimum deposition conditions by involving all other parameters that affect the deposition process. Thicker and better quality films have been obtained for both CdSO$_{4}$ and CdCl$_{2}$ cases. [Preview Abstract] |
Thursday, November 10, 2005 4:51PM - 5:03PM |
EB.00004: Properties of W-Ge-N as a diffusion barrier material for Cu. Seemant Rawal, David Norton, Tim Anderson, Lisa McElwee-White The properties of W-Ge-N thin films are reported, focusing on issues relevant to their use as diffusion barriers for Cu metallization on silicon. The amorphous W-Ge-N thin films were deposited on thermally grown SiO2/Si using reactive sputter deposition. This was followed by in-situ deposition of Cu films. Annealing studies for W-Ge-N were then carried out in vacuum to investigate Cu diffusion and barrier film crystallization. X-ray diffraction was used to assess the crystallinity of the films upon annealing. The results show that W-Ge-N has a recrystallization temperature that is higher that that for WNx. Auger electron spectroscopy was used to measure the depth profile of Cu diffusion through the barrier layer. Little or no Cu diffusion was detected for relatively high annealing temperature. The W-Ge-N films were conductive, although the resistivity is somewhat higher than that for WNx. The results suggest that W-Ge-N may be an attractive diffusion barrier material for Si or SiGe devices. [Preview Abstract] |
Thursday, November 10, 2005 5:03PM - 5:15PM |
EB.00005: MgCaO Dry Etching on GaN M. Hlad, L. Voss, B.P. Gila, C.R. Abernathy, S.J. Pearton, F. Ren MgCaO films grown by rf plasma-assisted Molecular Beam Epitaxy and capped with Sc$_{2}$O$_{3}$ are promising candidates as surface passivation layers and gate dielectrics on GaN-based high electron mobility transistors (HEMTs) and metal-oxide semiconductor HEMTs (MOS-HEMTs) respectively. Two different plasma chemistries were examined for etching these thin films on GaN. Inductively Coupled Plasmas of CH$_{4}$/H$_{2}$/Ar produced etch rates only in the range 20-70 {\AA}/min, comparable to the Ar sputter rates under the same conditions. Similarly slow MgCaO etch rates ($\sim $100 {\AA}/min) were obtained with Cl$_{2}$/Ar discharges under the same conditions, but GaN showed rates almost an order of magnitude higher. The MgCaO removal rates are limited by the low volatilities of the respective etch products. The CH$_{4}$/H$_{2}$/Ar plasma chemistry produced a selectivity of around 2 or etching the MgCaO with respect to GaN. [Preview Abstract] |
Thursday, November 10, 2005 5:15PM - 5:27PM |
EB.00006: Simulation of ZnO-based UV and Visible Light-Emitting Diode Structures Sang Youn Han, Hyucksoo Yang, D.P. Norton, S.J. Pearton, F. Ren, A. Osinsky, J.W. Dong, B. Hertog, P.P. Chow Two different types of ZnO-based LED structures have been examined using a 1-D simulator that accounts for specific features of the hexagonal semiconductors - strong piezoeffects, existence of spontaneous electric polarization, low efficiency of acceptor activation, and high threading dislocation density in the material. A hybrid ZnO/ZnCdO/AlGaN/GaN structure grown on sapphire avoids problems in achieving robust p-type doping in ZnO. An all-ZnO approach employs a MgZnO/ZnCdO/MgZnO double heterostructure grown on a ZnO substrate. The band diagram of each structure is examined with simulator considering the polarization effect within this material. And it is observed that the active layer thickness and doping are important factors effecting emission intensity in these structures and the effect of polarization effects on c-plane substrates needs further study. The hybrid ZnO/GaN approach provides an alternative for achieving robust p-type doping for ZnO-based LED that incorporates ZnCdO active regions with optimized doping and thickness. These results will be useful to identify the most important parameters for achieving high brightness and high performance in ZnO based LED structures. [Preview Abstract] |
Thursday, November 10, 2005 5:27PM - 5:39PM |
EB.00007: Stable Contacts at High Temperature for GaN using Boride-Metal Scheme. Rohit Khanna, Steve Pearton, C.J. Kao, Fan Ren, Ivan Kravchenko, G.C. Chi Ohmic contact having boride interlayer (Ti/Al/X/Ti/Au) to n-GaN was studied using contact resistance, scanning electron microscopy and Auger Electron Spectroscopy measurements. X in the metallization scheme was W$_{2}$B, TiB$_{2}$ or CrB$_{2}$. A minimum contact resistance of 7x10$^{-6 }\Omega $.cm$^{2}$ was achieved for W$_{2}$B based scheme at an annealing temperature of 800 \r{ }C. For TiB$_{2}$ it was of 2x10$^{-6 }\Omega $.cm$^{2}$ at 800$^{o}$C and 900$^{o}$C and 8x10$^{-6 }\Omega $.cm$^{2}$ for CrB$_{2}$ at 800$^{o}$C. Contact resistances were found to be essentially independent of measurement temperature, indicating that tunneling plays a dominant role in the current transport. The reliability measurements for the contact resistance of W$_{2}$B based contact showed excellent stability for extended periods at 200\r{ }C which simulates the type of device operating temperature that might be expected for operation of GaN-based power electronic devices. [Preview Abstract] |
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