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

We report on the demonstration and investigation of Ta2O5 as high-k dielectric for InAlN/GaN-MOS high-electron mobility transistor (HEMT)-on-Si. Ta2O5 of thickness 24 nm and dielectric constant similar to 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 similar to 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 Ta2O5/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 degrees C which has resulted into a flat band voltage spread (Delta V-FB) of 0.4 V and interface fix charge (Q(f)) of 3.98 x 10(13) cm(-2). X-ray photoelectron spectroscopy spectra of as-deposited and annealed Ta2O5 film were analyzed for Ta and O compositions in the film. The sample annealed at 500 degrees C has shown Ta:O ratio of 0.41. X-ray diffraction analysis was done to check the crystallization of amorphous Ta2O5 film at higher annealing temperatures.