β-(AlxGa1−x)2O3/Ga2O3 heterostructure Schottky diodes for improved VBR2/RON

Abstract

We propose and demonstrate the use of a β-(Al xGa1– x)2O3 capping layer to achieve increased breakdown voltage, VBR, and VBR2/ RON figure of merit in β-Ga2O3 Schottky diodes, where RON is the on-state resistance. We demonstrate that the addition of a 30 nm-thick β-(Al0.22Ga0.78)2O3 cap to an n-type β-Ga2O3 layer grown by metal organic chemical vapor deposition increases the breakdown voltage from 246 to 387 V in diodes with Pt contacts and 3 × 1016 cm−3 n-type doping. The cap increases the surface Schottky barrier with Pt, resulting in reduced carrier injection under reverse bias. The results are in good agreement with simulations which show that the addition of the capping layer enables the peak electric field at breakdown to increase from 2.5 to 3.6 MV/cm. Simulations further show that RON penalty associated with the (Al xGa1– x)2O3 cap can be almost completely eliminated by grading the capping layer. Thus, by raising the barrier height beyond the limit imposed by the metal work function and Fermi level pinning, the proposed heterojunction helps to improve VBR by reducing the reverse leakage current in ultrawide bandgap semiconductor diodes where bipolar doping remains a challenge.