Investigation of In Situ SiN as Gate Dielectric and Surface Passivation for GaN MISHEMTs

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 similar to 3 x 10(12) cm(-2)eV(-1) at the SiN/AlGaN interface. The MISHEMTs with a source-drain distance of 3 mu 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-th) stability was assessed by means of both negative and positive gate stress measurements, as well as temperature-dependent I-D-V-G measurements. We observed a minimal Vth shift of similar to 0.4 V under both 3000 s gate stress of V-GS = 4 V and up to 200 degrees 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 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-modeGaNMISHEMTs for high-efficiency power switching applications.