AVS 71 International Symposium and Exhibition

Abstract
Large band gap vertical GaN power devices have been developed for high efficiency switch devices in high-power applications [1]. These devices incorporate p-type GaN through Mg doping in selective regions. Precise control of dopant concentration is crucial for the electronic properties of semiconductor devices. However, interfacial diffusion or through defect migration of dopants during fabrication process or operation can degrade the performance. Dopant segregation at threading dislocations can induce current leakage and Mg diffusion during high temperature annealing was reported [2].

We analyzed a GaN device removed from a USB charger, purchased from the market, that contained the NV6125 microchip for power switching control. The microchip was mechanically de-processed at EAG down to the field-effect-transistor level , exposing the source/drain region for microstructural characterization. A ~0.5 um thick cross-section was made along the gate via Focused Ion Beam (FIB) and observed using Scanning Transmission Electron Microscopy (STEM). STEM observation confirmed a layered structure composed of dielectric oxide, metal contact, and p-type GaN and AlGaN layers on GaN. The GaN epi exhibits a high threading dislocation density (TDD) that we estimate to be ~1e9/cm^2. Using a simple 2-beam tilting strategy in STEM we were quickly able to identify each dislocation as either edge, screw, or mixed type.