Characterization of the interfacial electronic properties of oxide films on GaAs fabricated by in-situ molecular beam epitaxy

We have used room temperature photoreflectance spectroscopy to study interfacial electronic properties of various oxide-GaAs heterostructures. The samples, air-, Al/sub 2/O-, Ga/sub 2/O/sub x/-, and Ga/sub 2/O/sub 3/(Gd/sub 2/O/sub 3/)-GaAs, were fabricated by in-situ molecular beam epitaxy. Built-in electric fields are 48, 44, and 35 kV/cm for air-, Al/sub 2/O/sub 3/-, and Ga/sub 2/O/sub x/-GaAs samples, respectively, corresponding to the interfacial state density (D/sub it/) of 2.4, 2.2, and 1.9/spl times/10/sup 11/ cm/sup -2/ eV/sup -1/, respectively. For the Ga/sub 3/O/sub 3/(Gd/sub 2/O/sub 3/)-GaAs sample, the built-in electric field is negligibly small, indicating a very low interfacial stare density. Estimated by the low field limit criterion, D/sub it/ is less than 1/spl times/10/sup 11/ cm/sup -2/ eV/sup -1/. Our results are consistent with the previous data obtained using capacitance-voltage measurements in quasi-static/high frequency modes.