Borkovs'ka L. Role of macrodefects in electronic and ionic processes in crystals and epitaxial layers of II-VI compounds

Investigated object - CdS monocrystals and ZnSe/GaAs, ZnTe/GaAs epitaxial layers. The goal of investigations - elucidation of physical mechanisms of a number of reversible and irreversible processes that occur in II-VI semiconductor compounds under an external disturbance (illumination, heating, ultrasonic treatment) and are caused by the presence and interaction of macrodefects and mobile point defects, as well as clarification of the role of these processes in degradation of optical characteristics of light emitting devices based on these compounds. Methods of investigations - optical (absorption and reflectance spectroscopy), luminescent, photoelectrical (photoconductivity, thermostimulated conductivity), electron beam induced current, EPR. Based on the results of such investigations it was shown that dislocation decoration by points defects in CdS crystals leads to extension of fundamental band edge in long wavelength region due to state density tail formation in near dislocation regions. These eff ect is established to manifest itself in transformation of edge photoluminescence spectrum shape and degradation processes in electron beam pumped lasers. Effect of athermal gathering of donors on dislocations under pulse ultrasound is revealed. It is shown that photostimulated formation of shallow donors in CdS crystal volume is caused by dissociation of clusters which consist of cadmium atoms. Photoluminescence lines connected with macrodefects are identified in ZnTe/GaAs and ZnSe/GaAs epitaxial layers. It is shown that near surface region of these layers contain increased concentration of linear and point defects. Obtained experimental results can be used for improvement of growth technology conditions of II-VI monocrystals and epitaxial layers used for optoelectronic device creation.