Investigation of Ta₂O₅ as an Alternative High- ${k}$ Dielectric for InAlN/GaN MOS-HEMT on Si

We report on the demonstration and investigation of Ta ₂ O ₅ as high-k dielectric for InAlN/GaN-MOS high-electron mobility transistor (HEMT)-on-Si. Ta ₂ O ₅ of thickness 24 nm and dielectric constant ~30 was sputter deposited on InAlN/GaN HEMT and was investigated for different post deposition anneal (PDA) conditions. The gate leakage was 16 nA/mm at −15 V which was ~five orders of magnitude lower compared to reference HEMT. The 2-D electron gas (2-DEG) density was found to vary with annealing temperature suggesting the presence of net charge at the Ta ₂ O ₅ /InAlN interface. Dispersion in the capacitance–voltage ( ${C}$ – ${V}$ ) characteristics was used to estimate the frequency-dependent interface charge, while energy band diagrams under flat band conditions were investigated to estimate fixed charge. The optimum anneal condition was found to be 500 °C which has resulted into a flat band voltage spread ( $\Delta {V}_{\text {FB}}$ ) of 0.4 V and interface fix charge ( ${Q} _{\text {f}}$ ) of ${3.98} \times {10}^{{13}}$ cm $^{-2}$ . X-ray photoelectron spectroscopy spectra of as-deposited and annealed Ta ₂ O ₅ film were analyzed for Ta and O compositions in the film. The sample annealed at 500 °C has shown Ta:O ratio of 0.41. X-ray diffraction analysis was done to check the crystallization of amorphous Ta ₂ O ₅ film at higher annealing temperatures.