Low interface state density AlGaN/GaN MOSHFETs with photochemical vapor deposition SiO₂ layers

High quality SiO₂ was successfully deposited onto AlGaN by photo chemical vapor deposition (photo-CVD) using D₂ lamp as the excitation source. It was found that the interface state density was only 1.1 × 10¹¹ cm^-2 eV^-1. AlGaN/GaN metal-oxide-semiconductor heterojunction field effect transistors (MOSHFETs) were also fabricated with such photo-CVD oxide as the insulating layer. Compared with AlGaN/GaN metal-semiconductor HFETs (MESHFETs) with similar structure, it was found that we could reduce the gate leakage current by more than four orders of magnitude by inserting the 32 nm-thick photo-CVD SiO₂ layer between AlGaN/GaN and gate metal. With a 1 μm gate length, it was found that room temperature saturated I_ds, maximum g_m and gate voltage swing (GVS) of the fabricated nitride-based MOSHFET are 800 mA/mm, 86 mS/mm and 9 V, respectively.