Scanning Kelvin Probe Microscopic Study of Ni-(Al)GaN and Heterogeneous Integration of GaAs/GaN by Wafer Fusion

Scanning Kelvin probe microscopy was applied for the surface potential (SP) measurements across lateral Ni-(Al)GaN Schottky junctions. The bare surface barrier heights of unintentionally doped Al0.22Ga0.78N and n-GaN in air were estimated by comparing the SP of (Al)GaN and Ni. Under the 364.5 nm illumination, the surface barriers were observed to decrease and the surface photovoltage (SPV) was measured. Minority carrier diffusion length in n-GaN was extracted by modeling the SPV profile near the Schottky junction (Ni-GaN) for the first time. Heterogeneous integration of GaAs/GaN was obtained by wafer fusion. The p(n)-GaAs-GaN diodes and AlGaAs/GaAs/GaN heterojunction bipolar transistors (HBTs) were fabricated. Despite the poor performance of the fused HBT, the p-GaAs-GaN diodes prove the possibility of fabricating much improved fused HBTs after optimizing fusion and fabrication processes. For comparison, as-grown AlGaAs/GaAs/GaAs HBTs were fabricated, showing the current gain of 68 at IB= 20 å_ÌÎA and VCE= 2 V.