Cathodoluminescence study of pyramidal facets in piezoelectric InGaAs/GaAsmultiple quantum well pin photodiodes

A study of the optical and electrical activity of defects at the surface of InGaAs/GaAs multiple quantum well pin photodiodes was done on two differen t misoriented (111)B GaAs substrates: substrate A, misoriented 1 degrees to wards [(2) over bar 11] and substrate B, misoriented 2 degrees towards [<2( 11)over bar>]. In this article, we report the existence of different facete d defects at the surface with the misorientation and their influence on the optical performance. The surface of photodiodes grown on substrate A shows inclined pyramids with two enhanced facets. The electron beam induced curr ent measurements showed that these pyramids act as high efficient collector of the e-beam excited electron-hole pairs (e-h). This behaviour agrees wit h the reduction of the cathodoluminescence emission efficiency at the facet s. In contrast, a different pyramid type with one enhanced facet is observe d at the surface of diodes grown on substrate B. However, these facets have not shown either optic or electric activity. In these diodes, the dislocat ions localised at the active region degrade the device performance acting a s non-radiative recombination centres. (C) 1999 Elsevier Science Ltd. All r ights reserved.