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-grownin situSiN 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 thein situSiN 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~ 3× 10¹²cm⁻²eV⁻¹at the SiN/AlGaN interface. The MISHEMTs with a source–drain distance of3~μ mshow a maximum drain current of 1560 mA/mm and a high on/off current ratio of10⁹. The device threshold voltage (Vₜh) stability was assessed by means of both negative and positive gate stress measurements, as well as temperature-dependentID–VGmeasurements. We observed a minimalVₜhshift of ~0.4 V under both 3000 s gate stress ofVGS= 4V and up to 200 °C thermal stimulation. Furthermore, combining thein situSiN with plasma-enhanced chemical vapor deposition SiN, we developed a bilayer passivation scheme for effective suppression of current collapse. Employing the high-qualityin situSiN, we have demonstrated large-area GaN MISHEMTs on Si with a gate width of 20 mm, showing a low off-state leakage of2~μ A/mm at 600 V and a low dynamic/static ON-resistance ratio. The device results show great advantages of employingin situSiN in D-mode GaN MISHEMTs for high-efficiency power switching applications.