Impact of Substrate Imperfections on Epitaxial Layer Quality

摘要

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.