SciTech Connect

Title: Materials physics and device development for improved efficiency of GaN HEMT high power amplifiers.

Materials physics and device development for improved efficiency of GaN HEMT high power amplifiers. GaN-based microwave power amplifiers have been identified as critical components in Sandia's next generation micro-Synthetic-Aperture-Radar (SAR) operating at X-band and Ku-band (10-18 GHz). To miniaturize SAR, GaN-based amplifiers are necessary to replace bulky traveling wave tubes. Specifically, for micro-SAR development, highly reliable GaN high electron mobility transistors (HEMTs), which have delivered a factor of 10 times improvement in power performance compared to GaAs, need to be developed. Despite the great promise of GaN HEMTs, problems associated with nitride materials growth currently limit gain, linearity, power-added-efficiency, reproducibility, and reliability. These material quality issues are primarily due to heteroepitaxial growth of GaN on lattice mismatched substrates. Because SiC provides the best lattice match and thermal conductivity, SiC is currently the substrate of choice for GaN-based microwave amplifiers. Obviously for GaN-based HEMTs to fully realize their tremendous promise, several challenges related to GaN heteroepitaxy on SiC must be solved. For this LDRD, we conducted a concerted effort to resolve materials issues through in-depth research on GaN/AlGaN growth on SiC. Repeatable growth processes were developed which enabled basic studies of these device layers as well as full fabrication of microwave amplifiers. Detailed studies of the GaN and AlGaN growth of SiC were conducted and more » techniques to measure the structural and electrical properties of the layers were developed. Problems that limit device performance were investigated, including electron traps, dislocations, the quality of semi-insulating GaN, the GaN/AlGaN interface roughness, and surface pinning of the AlGaN gate. Surface charge was reduced by developing silicon nitride passivation. Constant feedback between material properties, physical understanding, and device performance enabled rapid progress which eventually led to the successful fabrication of state of the art HEMT transistors and amplifiers. « less
Authors: ; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
OSTI Identifier:883465
Report Number(s):SAND2005-7587
TRN: US200614%%711
DOE Contract Number:AC04-94AL85000
Resource Type:Technical Report
Data Type:
Research Org:Sandia National Laboratories
Sponsoring Org:USDOE
Country of Publication:United States
Language:English
Subject: 36 MATERIALS SCIENCE; AMPLIFIERS; DISLOCATIONS; EFFICIENCY; ELECTRICAL PROPERTIES; ELECTRON MOBILITY; ELECTRONS; FABRICATION; FEEDBACK; MICROWAVE AMPLIFIERS; NITRIDES; PASSIVATION; PHYSICS; POWER AMPLIFIERS; RELIABILITY; ROUGHNESS; SILICON NITRIDES; SUBSTRATES; THERMAL CONDUCTIVITY; TRANSISTORS Synthetic Aperture Radar.; Gallium nitride-Electric properties.; Power amplifiers-Design and construction.