Interaction of Multicharge Impurities with Dislocations in Germanium Single Crystals

Abstract

Germanium is a relevant object for research into the influence of dislocations on electronic properties of impurities and conversely the influence of impurities on electronic states of dislocations owing to high structural perfection of germanium single crystals and the abundant data available on properties of impurities and defects. We present the results of studies of radiationless and radiation recombination (by the DLTS and photoluminescence (PL) methods, respectively) of charge carriers in deep levels of plastically deformed germanium single crystals doped with multicharge copper or gold impurities by the diffusion method. The recombination parameters (position of the energy levels in the forbidden gap, the value and activation energy of capture cross−section and ionization entropy) of Cu−2/−3 and Au−1/−2 ions determined by DLTS are independent of dislocation density and in good agreement with those in as−grown samples, which is explained by their position outside the Reed cylinders. The parameters of Cu−2 and Au−1 electron capture account for the dependence of the DLTS signal amplitude on filling pulse frequency. After copper doping the methods of transmission electron microscopy (TEM) revealed no precipitates between the dislocations. The intensity of radiation recombination on dislocations at 4.2 K is significantly reduced by copper doping and restored by heating the samples at temperatures above 500 °С as a result of copper diffusion from the bulk toward the dislocations. The specific features of the luminescence spectra of the heated copper−doped samples within the temperature range 200—400 °C are likely to be due to the reactions of the impurities accumulated near the dislocations on cooling the copper−doped samples.