Nonradiative ’’large dark spots’’ in AlxGa1−xAs-GaAs heterostructures

Abstract

A detailed study of ’’large dark spots’’ (LDS) in heterostructures is carried out. LDS are broad nonradiative regions extending up to several hundred microns away from the site of visible damage to the top surface of the sample. We show that only samples with p-n junctions exhibit LDS. In these samples, most of the photogenerated minority carriers diffuse across the junction. A forward bias develops across the (uncontacted) p-n junction, and photoluminescence arises from the forward junction current. In a damaged sample under uniform illumination, some of the forward current flows to the defect where the carriers recombine nonradiatively. Voltage drops produced by the current flowing (parallel to the junction) to the defect reduce the junction bias and luminescence near the defect. A theory is developed which accounts for the size and shape of the LDS.