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This work demonstrates the low temperature thin-film deposition of silicon nitride (SiNx) for III-nitride-based high electron mobility transistors using inductively coupled plasma chemical vapor deposition. It is observed that the nonlinear dependency of the deposition temperature and gas flow rates have a profound impact on the film quality. The process parameter space is scanned and the optimum film quality is achieved, which is verified with physical and electrical characterizations. The best quality film is achieved at a deposition temperature of 380 °C demonstrating near ideal stoichiometry with negligible hydrogen (<5%) and oxygen (<3%) concentrations. In addition, the optimized film is found to have zero pinholes even at a thickness of 10 nm and is uniform over a large area with an rms roughness of 0.58 nm. The deposited films are characterized by atomic force microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The dielectric strength and dielectric constant of these films are determined from current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the metal-insulator-metal structure, respectively. For the best quality film, the values of dielectric strength and dielectric constant are measured to be ∼8 MV/cm and ∼7.5, respectively. A metal-insulator-semiconductor-heterostructure (metal/SiNx/AlGaN/GaN) capacitor is fabricated with the optimized recipe for interface characterization. The density of slow traps is determined from the hysteresis in the C-V curve and found to be 7.38×1010 cm−2. The frequency dependent conductance method is also used to investigate the trap density. The trap state density is found to be 1.67×1012 cm−2 eV−1 at 0.29 eV below conduction band.

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This work demonstrates performance improvements in AlGaN/GaN metal–insulator–semiconductor high‐electron‐mobility transistors (MIS‐HEMTs) using low‐temperature inductively coupled plasma chemical vapor deposited (ICP–CVD) silicon nitride (SiN x ). The low‐temperature SiN x is used for both device passivation and gate dielectric. The bandgap of SiN x (4.9 eV) and AlGaN/SiN x type‐II staggered band alignment (ΔE c  = 1.4 eV) are determined using ultraviolet‐visible spectroscopy and ultraviolet photoelectron spectroscopy, respectively. The SiN x layer effectively increases the in‐plane tensile strain in the AlGaN barrier layer. The tensile strain increases by 0.08% for a 150 nm SiN x layer. The corresponding increase in the piezoelectric polarization and 2D electron gas (2DEG) density is 1.5 × 1012 and 1.44 × 1012 cm−2, respectively. The transistor's on‐resistance decreases to 9.33 Ω mm compared with 14 Ω mm measured for the control devices with gate length 1 μm and source and drain separation of 11 μm. The gate leakage current reduces by more than three orders of magnitude. The I ON/I OFF ratio increases by two orders of magnitude. The improvements in the physical and electrical properties of the low‐temperature‐deposited ICP–CVD SiN x MIS‐HEMTs make it a viable candidate for low‐thermal‐budget fabrication. This nitride can be used with non‐alloyed Ohmic contacts on GaN for extremely low‐thermal‐budget transistors.

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