Investigation of <italic>In Situ</italic> SiN as Gate Dielectric and Surface Passivation for GaN MISHEMTs

Abstract

In this paper, we present a systematic investigation of metal–organic chemical vapor deposition-grown in situ SiN as the gate dielectric and surface passivation for AlGaN/GaN metal insulator semiconductor high electron mobility transistors (MISHEMTs). The dielectric constant and breakdown field of the in situ SiN were extracted from devices with varied gate dielectric thicknesses. Using frequency-dependent capacitance–voltage and parallel conductance methods, we obtained a low trap density of $\sim 3\times 10^{12}$ cm $^{-2}$ eV $^{-1}$ at the SiN/AlGaN interface. The MISHEMTs with a source–drain distance of $3~\mu \text{m}$ show a maximum drain current of 1560 mA/mm and a high on/off current ratio of $10^{9}$ . The device threshold voltage ( ${V}_\textsf {th}$ ) stability was assessed by means of both negative and positive gate stress measurements, as well as temperature-dependent $ {I}_\textsf {D}$ – ${V}_\textsf{G}$ measurements. We observed a minimal $ {V}_\textsf{th}$ shift of ~0.4 V under both 3000 s gate stress of ${V}_\textsf {GS}= 4$ V and up to 200 °C thermal stimulation. Furthermore, combining the in situ SiN with plasma-enhanced chemical vapor deposition SiN, we developed a bilayer passivation scheme for effective suppression of current collapse. Employing the high-quality in situ SiN, we have demonstrated large-area GaN MISHEMTs on Si with a gate width of 20 mm, showing a low off-state leakage of $2~\mu \text{A}$ /mm at 600 V and a low dynamic/static ON-resistance ratio. The device results show great advantages of employing in situ SiN in D-mode GaN MISHEMTs for high-efficiency power switching applications.