Robust SiNx/GaN MIS-HEMTs With Crystalline Interfacial Layer Using Hollow Cathode PEALD

In this letter, we report gallium nitride-based metal-insulator-semiconductor high-electron-mobility transistors (GaN MIS-HEMTs) with a 16-nm-thick silicon nitride (SiN
_x
) gate insulator and surface passivation layer grown using low-temperature (300 °C) hollow cathode plasma-enhanced atomic layer deposition. Tris(dimethylamino) silane and a remote N
₂
plasma were used as the silicon precursor and the nitrogen co-reactant, respectively. Though the growth temperature was as low as 300 °C, we obtained excellent film properties such as a high refractive index (2.00), a high film density (2.9 g/cm
³
), and a low wet etch rate (0.8 nm/min)in 100:1 hydrofluoric acid. High-resolution transmission electron microscopy images of the gate stacks showed ~1.5 nm β-phase Si
₃
N
₄
crystalline interfacial layer on the GaN surface. The devices showed a negligible hysteresis of ~50 mV, a steep subthreshold slope of 76 mV/dec, and a high
_ON/OFF
drain current ratio of ~10
⁹
. In addition, the devices showed a small positive/negative bias temperature threshold voltage (V
_th
) instability (ΔV
_th
≤ 0.2 V at 25 °C and 150 °C) as well as a mitigated current collapse under an off-state quiescent V
_DS
of 20 V.