RADIATIVE RECOMBINATION AT SURFACE AND NEAR-SURFACE STRUCTURE DEFECTS IN GaAs.

An investigation was made of the influence of the surface damage (caused by various means) on the low-temperature photoluminescence spectra excited in n-type GaAs single crystals by laser radiation. The surface damage was caused by 400 keV electron beams, gamma rays in doses of 10**6-10**7 rad, high-power laser beams, argon ion bombardment, or doping with Au and Cu atoms from an aqueous solution. These types of damage influence differently the edge (1. 51 eV) and long-wavelength (1. 22 eV) radiative recombination. New photoluminescence bands of surface origin were found at 1. 39 and 1. 41 eV. According to the proposed model, the 1. 39 eV peak was due to structure defects which appeared on the surface (they were probably vacancy clusters), whereas the 1. 41 eV peak was due to complexes formed from structure defects (vacancies) and Au or Cu atoms. The depth of spatial localization of various luminescence centers was estimated. The nature of the dependence of the luminescence band intensities on the gamma -ray dose could be used to distinguish between various types of luminescence peaks of surface origin. Anomalous luminescence after cleaving was also observed.