Traps and Defects in AlGaN-GaN High Electron Mobility Transistors on Semi-Insulating SiC Substrates

Abstract

High electron mobility transistors (HEMTs) based on AlGaN-GaN hetero-structures are promising for high power, high speed, and high temperature operation. Especially, AlGaN-GaN HEMTs grown on semi-insulating (SI) SiC substrates are the most promising for both military and commercial applications. High performance characteristics from these devices are possible in part due to the presence of high two-dimensional electron gas charge sheet density maintaining a high Hall mobility at the AlGaN barrier-GaN buffer hetero-interface and in part due to high thermal conductivity of the SiC substrates. However, long-term reliability of these devices still remains a major concern because of the large number of traps and defects present both in the bulk as well as at the surface leading to undesirable characteristics including current collapse. We report on the study of traps and defects in two MOCVD-grown structures: Al 0.27 Ga 0.73 N HEMTs on SI SiC substrates and Al 0.27 Ga 0.73 N Schottky diodes on conducting SiC substrates. Our HEMT structures consisting of undoped AlGaN barrier and GaN buffer layers grown on an AlN nucleation layer show a charge sheet density of ~10 13 /cm 2 and a Hall mobility of ~1500cm 2 /V⋅sec. Deep level transient spectroscopy (DLTS) was employed to study traps in AlGaN Schottky diodes and HEMTs fabricated with different Schottky contacts consisting of Pt-Au and Ni-Au. Focused ion beam was employed to prepare both cross-sectional and plan view TEM samples for defect analysis using a high resolution TEM.

Traps and defects in pre‐ and post‐ stressed AlGaN–GaN high electron mobility transistors

“…Mizutani 7 also reported these traps from 1.5‐µm gate AlGaN/GaN MIS‐HEMTs and our group recently reported the same traps from AlGaN Schottky diodes using capacitance mode DLTS 8. I‐DLTS spectra measured from sample B also showed two dominant peaks (data not shown here), but the ∼0.5 eV traps from sample B showed a much smaller increase in density as compared to sample A after the stress test.…”

“…I‐DLTS spectra measured from sample B also showed two dominant peaks (data not shown here), but the ∼0.5 eV traps from sample B showed a much smaller increase in density as compared to sample A after the stress test. The ∼0.5 eV traps, attributed to N anti‐sites, originate from the AlGaN barrier 8.…”