Liquid-phase deposition of Al₂O₃ thin films on GaN

Thin films of aluminum oxide (Al2 O3) on GaN substrates were grown by the process of low-temperature liquid-phase deposition (LPD), in which aluminum sulfate with crystallized water [Al2 (SO4) 3 18 H2 O] and sodium bicarbonate [NaHCO3] were used as the precursors. The pH value of the growth solution plays an important role in the deposition process. The best quality of the oxide thin film was obtained at the pH value of 3.80, while the growth rate was 35 nmh at the optimized concentration values of Al2 (SO4) 3 =0.0834 molL and NaHCO3 =0.211 molL and at the temperature of 30°C. The films were characterized by means of X-ray photoelectron spectroscopy, Auger electron spectroscopy, and atomic force microscopy. It was found that the leakage current density of 50 nm thin Al2 O3 oxide film was between 10-4 and 10-5 A cm2 at a negative electric field of 1 MVcm, with the breakdown electric field being greater than 10 MVcm. After annealing the oxide at 750°C for 30 min, the leakage current density was lowered to the value of 10-6 - 10-7 A cm2 at the negative electric field of 1 MVcm. The oxide-semiconductor interface state density as calculated from the capacitance-voltage curve was 3.89× 1011 cm-2 eV-1.