Novel High Efficiency Photovoltaic Devices Based on the III-N Material System

Issued as final repor

DURIP: ultra high vacuum scanning probe system for investigation of novel..

Issued as final reportUnited States. Army Research Offic

Fundamental understanding, characterization, passivation and gettering of electrically active defects in silicon

Ph.D.Ajeet Rohatg

Multiferroic materials for next-generation power amplifiers

Issued as final reportUnited States. Air Forc

CAREER: New device opportunities enabled by polar dielectric and semiconductor heteroepitaxy

Issued as final reportNational Science Foundation (U.S.

Heat dissipation in high-power GaN electronics on thermally resistive substrates

© 2005 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.DOI: 10.1109/TED.2005.851815The heat dissipation in GaN devices grown on low thermal conductivity lithium gallate (LGO) substrates was investigated. The thermal conductivity of single-crystal LGO was measured utilizing the 3ω technique for temperatures ranging from 100 K–500 K. For the GaN layer, the thermal conductivity was estimated using a phonon transport model which included dislocation density and temperature dependence. These data were then used in a finite element program to determine the thermal behavior of a heterojunction field-effect transistor. Based on a maximum junction temperature of 500 K, it was found that devices with a power dissipation of 1W/mm were possible if the primary heat dissipation path was through the low thermal conductivity substrate. However, in using a front side cooling scheme, results suggest that it may be possible to develop devices with power dissipation in the range of 10 W/mm

Leaky surface acoustic waves in Z-LiNbO ₃ substrates with epitaxial AlN overlays

© 2004 American Institute of Physics. The electronic version of this article is the complete one and can be found at: http://dx.doi.org/10.1063/1.1805705DOI: 10.1063/1.1805705The properties of leaky surface acoustic waves (LSAW) in MBE grown AIN layer on Z-cut LiNbO₃ structures have been studied by numerical simulation and experimental measurements and compared with those of Rayleigh waves in the same structure. In the range of AIN layer thicknesses studied (0<kh<0.145) the measured velocity of LSAW propagating along the X axis of LiNbO3 substrate was essentially constant at around 4400 m∕s. The measured electromechanical coupling coefficients (K²) for the LSAW are roughly 1/4 of the predicted values, which might be due to the strong attenuation of the leaky wave unaccounted for during the parameter extraction. The thin AIN film slightly improved the measured temperature coefficient of frequency for the LSAW over that attained for the Z-cut, X-propagating LiNbO₃ substrate alone

Wet-based digital etching on GaN and AlGaN

Department of Defense (DoD

Stable and High Performance AlGaN Self-Aligned-Gate Field Emitter Arrays

AlGaN alloys are promising for field emission devices due to their low electron affinities. However, there have been limited demonstrations of AlGaN vacuum transistors so far. This paper combines a new self-alignedgate (SAG) process and digital-etching tip sharpening to demonstrate three-terminal AlGaN SAG field emitter arrays (FEAs). These devices show a turn-on voltage of 19.5 V and an anode current density (JA) of 100 mA/cm2 at an overdrive voltage of 20 V, which are comparable with best Si devices. The AlGaN SAGFEAs can operate in DC mode at a fixed gate-emitter voltage (VGE) with JA of 3-5 mA/cm2 for at least 5 hours without a significant degradation. The gate leakage does not increase after the long DC operation, suggesting high-performance and stable AlGaN vacuum transistors.AFOSR through MURI ESE progra