Comparison of resonant tunneling diodes grown on freestanding GaN substrates and sapphire substrates by plasma-assisted molecular-beam epitaxy*

Abstract

AlN/GaN resonant tunneling diodes (RTDs) were grown separately on freestanding GaN (FS-GaN) substrates and sapphire substrates by plasma-assisted molecular-beam epitaxy (PA-MBE). Room temperature negative differential resistance (NDR) was obtained under forward bias for the RTDs grown on FS-GaN substrates, with the peak current densities (J p) of 175–700 kA/cm2 and peak-to-valley current ratios (PVCRs) of 1.01–1.21. Two resonant peaks were also observed for some RTDs at room temperature. The effects of two types of substrates on epitaxy quality and device performance of GaN-based RTDs were firstly investigated systematically, showing that lower dislocation densities, flatter surface morphology, and steeper heterogeneous interfaces were the key factors to achieving NDR for RTDs.