Investigation of the fabrication processes of AlGaN/AlN/GaN НЕМТs with in situ Si$_{3}$N$_{4}$ passivation

The optimum mode of the in situ plasma-chemical etching of a Si$_{3}$N$_{4}$ passivating layer in C$_{3}$F$_{8}$/O$_{2}$ 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 Si$_{3}$N$_{4}$ 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 Si$_{3}$N$_{4}$ 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 Si$_{3}$N$_{4}$ than without it.