Silicon Substrate Removal of GaN DHFETs for Enhanced (> 1100 V) Breakdown Voltage

In this letter, we present a novel approach to enhance the breakdown voltage (V-BD) for AlGaN/GaN/AlGaN double-heterostructure FETs (DHFETs), grown by metal-organic chemical vapor deposition on Si (111) substrates through a silicon-substrate-removal and a layer-transfer process. Before removing the Si substrate, both buffer isolation test structures and DHFET devices showed a saturation of V-BD due to the electrical breakdown through the Si substrate. We observed a VBD saturation of 500 V for isolation gaps larger than 6 mu m. After Si removal, we measured a V-BD enhancement of the AlGaN buffer to 1100 V for buffer isolation structures with an isolation gap of 12 mu m. The DHFET devices with a gate-drain (L-GD) distance of 15 mu m have a V-BD > 1100 V compared with similar to 300 V for devices with Si substrate. Moreover, from Hall measurements, we conclude that the substrate-removal and layer-transfer processes have no impact on the 2-D electron gas channel properties.