Spectroscopic Ellipsometry of Porous n-GaAs

Abstract

Spectroscopic ellipsometry studies were carried out on porous n-GaAs samples formed by electrochemical etching in HF-based electrolytes. The substrates of n-GaAs : Te (n~1018 cm–3) and n-GaAs:Cr (n~1014 cm–3) were etched in solutions of (1 : 1) HF : H2O and (15 : 1 : 1) HF : C2H5OH : H2O, respectively, at various etching times (1 – 30 min) and current densities (30 – 100 mA/cm2). The morphology of porous n-GaAs samples was investigated using standard scanning electron microscope (SEM) and atomic force microscope (AFM) techniques. The optical response of porous n-GaAs was studied by means of a photometric ellipsometer in the range 1 – 5 eV. The spectral dependence of experimentally determined ellipsometric parameters was interpreted in the model simulating the complex porous n-GaAs sample as a multilayer structure. A correlation between structural and optical parameters was revealed. The effective parameters obtained in the fitting procedure were used for a characterization of porous n-GaAs samples.