Optimization of GaN Channel Conductivity in AlGaN/GaN HFET Structures Grown by MOVPE

Abstract

Optimization of GaN channel conductivity in AlGaN/GaN Heterojunction Field Effect Transistor (HFET) structures was performed using High Resistivity (HR) GaN templates grown by Metal-organic Vapor Phase Epitaxy (MOVPE). The GaN sheet resistance was tuned using final nucleation layer (NL) annealing temperature. Using an annealing temperature of 1033°C, GaN with sheet resistance of 10 Ω/sq was achieved, comparable to that of Fe-doped GaN. X-Ray Diffraction (XRD) and Photoluminescence (PL) analysis show that the high resistance GaN is achieved due to compensating acceptor levels introduced through edge-type threading dislocations. XRD analysis also shows optimization of annealing temperature provided a means to maximize GaN sheet resistance without significantly degrading material quality. AlGaN/GaN HFET layers grown using HR GaN templates gave surface and interface roughness of 14 and 7 Å, respectively. The 2DEG Hall mobility and sheet charge of HFETs grown using HR GaN templates was comparable to similar layers grown using unintentionally doped (UID) GaN templates.