Investigation of the fabrication processes of AlGaN/AlN/GaN НЕМТs with in situ Si3N4 passivation

Abstract

The optimum mode of the in situ plasma-chemical etching of a Si₃N₄ passivating layer in C₃F₈/O₂ medium is chosen for the case of fabricating AlGaN/AlN/GaN НЕМТs. It is found that a bias of 40–50 V at a high-frequency electrode provides anisotropic etching of the insulator through a resist mask and introduces no appreciable radiation-induced defects upon overetching of the insulator films in the region of gate-metallization formation. To estimate the effect of in situ Si₃N₄ growth together with the heterostructure in one process on the AlGaN/AlN/GaN НЕМТ characteristics, transistors with gates without the insulator and with gates through Si₃N₄ slits are fabricated. The highest drain current of the AlGaN/AlN/GaN НЕМТ at 0 V at the gate is shown to be 1.5 times higher in the presence of Si₃N₄ than without it.