Improved interface properties of Al₂O₃ optical coatings on GaAs deposited by e-beam

We report the results of the improved surface passivation of GaAs using Al2O3 films deposited by the e-beam evaporation technique. A low and stable density of the negative fixed interface charge density of ~1 × 1010 cm−2 and the fast interface state density of <3 × 1011 cm−2 eV−1 were obtained for the said films. Furthermore, using dc I–V measurements near zero bias, the typical leakage currents varying from 4 to 90 pA range were measured. The lowest near zero bias current was 0.5 pA which indicates a resistivity of 3.6 × 1011 Ω cm for our Al2O3 films, which is comparable to the values reported in the literature. To assess the uniformity of these films, a large number of devices from the 2 inch wafer were measured. It was observed that in general the shape of C–V curves remains the same except that there is only a 15% variation in accumulation capacitance across the whole wafer. This suggests a variation of dielectric constant from 4 to 4.5, which is indicative of acceptable film uniformity. Similarly, resistivity varied by three orders of magnitude from ~3.0 × 108 to ~3 × 1011 Ω cm.