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 (ΔV
_FB
) of 0.4 V and interface fix charge (Q
_f
) of 3.98 × 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.