Extrinsic electroabsorption in high−resistivity GaAs

Abstract

We report here what we believe to be the first detailed investigation of extrinsic electroabsorption in a semiconductor for photon energies much less than the band gap. Apparatus capable of measuring a field−induced absorption constant change as small as 10⁻⁵ cm⁻¹ was applied to a GaAs : O crystal with 300 °K Fermi level of 0.54 eV below the conduction band. Eleven pieces of major structure were detected at 300 and 80 °K between 0.52 and 1.39 eV, and variations of structure with light polarization, applied field, temperature, preillumination, and lock−in amplifier phase angle are reported. Both a first−harmonic and second−harmonic spectrum are obtained; the former is attributed to a Stark shifting of permanent dipole moments, and the latter to induced dipole character of the imperfections involved. Correlation between electroabsorption measurements and independent observations of photoconductivity, optical quenching, thermally stimulated conductivity, and space−charge injection is discussed.