Surface treatment on the growth surface of semi‐insulating GaN bulk substrate for III‐nitride heterostructure field‐effect transistors

Abstract

Al0.25Ga0.75N/GaN heterostructure field‐effect transistor (HFET) structures are grown on semi‐insulating GaN substrates by metalorganic chemical vapor deposition with Fe‐doped GaN buffer layer and various surface treatments prior to the epitaxial growth of the structure. The surface treatments are intended to remove suspected surface‐charge‐containing layer and they include wet chemical etching, in‐situ thermal etching, plasma dry etching, and photo‐enhanced chemical etching. Photo‐enhanced chemical (PEC) etching was effective in achieving microscopically smooth surface and in eliminating surface charge layer on the surface of semi‐insulating GaN substrates. RMS surface roughness of PEC etched surface of the semi‐insulating GaN substrate is 0.1∼0.2 nm for 1×1 μm2 scan. C ‐V measurement shows well‐defined 2‐dimensional‐gas‐related charge without any growth‐interface‐related charge for a HFET grown on a semi‐insulating GaN substrate with optimized photo‐enhanced chemical etching of the surface. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Physical Properties of AlGaN/GaN Heterostructures Grown on Vicinal Substrates

“…The origin of this additional charge is suspected to be related to the slicing and chemomechanical polishing of the bulk GaN substrate. 27 The interfacial Si enables substantial buffer leakage, which potentially limits use of heterostructures on these substrates for electronic devices unless the influence of the interfacial charge can be negated. Figure 1a shows a schematic of the structure grown in a two-step process.…”

Abnormal increase of 2DEG density in AlGaN/GaN HEMT grown on free-standing GaN substrate

“…However, Si impurities are more difficult to remove completely by substrate-cleaning methods such as chemical etching and in situ heat treatment than are C or O. [10][11][12] Si is considered to be a shallow donor impurity in GaN, the thermal ionization energies reported in the literature vary but are mostly below 30 meV. At present, it is believed that the reason for the increase of 2DEG density in the AlGaN/GaN HEMT structures grown on GaN substrates is related to Si impurities.…”