Impact of
Substrate Imperfections on Epitaxial Layer Quality
Michael Wojtowicz,
Randy Sandhu, Ben Heying, and Thomas Block
Northrop Grumman
Space Technology
One
(310)814-1713 /
mike.wojtowicz@trw.com
Ben Poust and Mark
Goorsky
Department of
Materials Science and Engineering
(310)206-0267 / goorsky@seas.ucla.edu
Abstract
We examined the role of
substrate quality on the epitaxial layer structure and performance of
pseudomorphic InGaAs/AlGaAs/GaAs and AlGaN/GaN/SiC high electron mobility
transistors (HEMTs). High resolution x-ray diffraction, high resolution x-ray
topography, and transmission electron microscopy proved essential. For the
GaAs-based pseudomorphic HEMT (pHEMT), the epitaxial layer misfit dislocation
density is always lower for a given channel composition and thickness when
grown on substrates with lower threading dislocation densities. Furthermore,
device electrical performance can be improved through increasing the channel
thickness to a greater degree when grown on lower threading dislocation
substrates. For the GaN-based HEMTs, the
SiC substrates show scratches, micropipes, and various crystal distortions that
impact the quality of the epitaxial material. High resolution x-ray topographs
of processed HEMT materials enable evaluation of the impact of both micropipes
and crystal distortion on the device performance.