Optical Properties of GaAs and Its Electrochemically Grown Anodic Oxide from 1.5 to 6.0 eV

Abstract

Spectroscopic ellipsometry has been used to nondestructively study the optical and interface properties of the grown anodic oxide system over the energy range 1.5–6.0 eV. Values of the dielectric function of differ by up to 30% from previously published spectra due to improved sample preparation techniques. Values of the dielectric function of the oxide agree within several percent with previous measurements. Upper limits to the thickness of a layer modeled as amorphous arsenic (a‐As) at the interface are 3 and 10Å for 60 and 75V oxides grown on B and surfaces, respectively, at 0.1 mA cm⁻² constant current in a phosphoric acid/glycol based electrolyte. The major discrepancy between measurements and ideal three‐phase model calculations arise from the interface region between oxide and ambient. This region shows a total distributed density deficit equivalent to 10Å lost material, probably due to leaching of . A complete description of the optical properties of the oxide requires a small absorptive component in the nominally transparent energy range below 4.5 eV. This absorptive component is equivalent to 0.2% and 0.9% by volume of a‐As for the 60 and 75V oxides, respectively. The infrared refractive indexes for the two oxides, calculated from a Sellmeier dispersion relation with the absorptive component removed, are 1.777 and 1.717, respectively.