Growth, Electrical Characterization, and Electroluminescence of GaN/SiC Heterojunction Diodes and Bipolar Transistors Fabricated on SiC Off-Axis Substrates

Abstract

The growth, electrical characterization, and electroluminescence (EL) of GaN/SiC heterojunction bipolar transistors (HBTs) are presented. GaN grown on off-axis SiC by molecular beam epitaxy showed step bunching owing to the large off-angle of SiC substrates, which contributed to the annihilation of edge dislocations. We investigated the impact of base doping concentration and SiC polytype (4H and 6H) on the characteristics of GaN/SiC heterojunction diodes. By utilizing a reduced doping concentration of 1×1018 cm-3 instead of 1×1019 cm-3, we suppressed the tunneling current via interface traps, resulting in an improved rectifying behavior in the diodes. Capacitance–voltage (C–V) and EL characteristics revealed that the band lineup of GaN/SiC is of type II, and 6H-SiC is better for electron injection. In accordance with diode characteristics, the fabricated GaN/SiC HBTs showed an improved common-base current gain of 0.03 by employing a reduced base doping concentration of 1×1018 cm-3 and 6H-SiC, whereas a current gain below 1×10-4 was obtained in the HBTs with a base doping concentration of 1×1019 cm-3.