High-Voltage Vertical GaN p-n Diodes by Epitaxial Liftoff From Bulk GaN Substrates

Abstract

High-performance vertical GaN-based p-n junction diodes fabricated using bandgap selective photoelectrochemical etching-based epitaxial liftoff (ELO) from bulk GaN substrates are demonstrated. The epitaxial GaN layers and pseudomorphic InGaN release layer were grown by MOCVD on bulk GaN substrates. A comparison study was performed between devices after liftoff processing (after transfer to a Cu substrate) and nominally identical control devices on GaN substrates without the buried release layer or ELO-related processing. ELO and bonded devices exhibit nearly identical electrical performance and improved thermal performance, compared with the control devices on full-thickness GaN substrates. The breakdown voltage, ideality factor, and forward turn-ON performance were found to be nearly identical, indicating that the transfer process does not degrade the quality of the p-n junctions. The devices exhibit turn-ON voltages of 3.1 V at a current density of 100 A/cm2, with a specific ON-resistance ( ${R} _{ \mathrm{\scriptscriptstyle ON}}$ ) of 0.2–0.5 $\text{m}\Omega \cdot \text {cm}^{{2}}$ at 5 V and a breakdown voltage ( ${V} _{\text {br}}$ ) of 1.3 kV. Both optical and electrical characterization techniques show that the thermal resistance of ELO devices bonded to a Cu carrier is approximately 30% lower than that for control devices on GaN substrates.