Structural characterization of molecular beam epitaxy grown ZnSe-based layers on GaAs substrates for blue-green laser diodes

ZnSe Films and fully developed p-on-n laser structures, including CdZnSe-ac tive and ZnSSe-guiding layers were grown by molecular beam epitaxy (MBE) on lattice matched p-GaAs, p-A1GaAs and p-GaInP buffer layers. The structural characteristics of these layers were studied by combined cross-section and planar view transmission electron microscopy (TEM). The defect density of the ZnSxSe1-x epilayers was shown to be very low, < 10(5) cm(-2). However, on their interfaces with the GaAs substrate, a high density of small disloc ation loops and clusters of the order of 3 x 10(10) cm(-2) was observed. In situ TEM experiments revealed that dislocations and stacking faults (SFs) were generated under the electron beam influence. From them, the perfect di slocations were confined at the ZnSe/GaAs interface, while the SFs propagat ed to the ZnSe overgrowth or the GaAs substrate, having one of their partia l dislocations at the interface. The generation of dislocations under the e lectron beam was not related to radiation damage but to thermal strain, whi ch was developed by the heating effect due to differential thermal dilatati on. Defects around the active zone of fully developed p-on-n laser structur es were also studied. The nature of such defects was defined by Burgers vec tor determination experiments. The critical role of growth variations, such as compositional changes resulting in strain, in the MBE process of Il-VI materials was demonstrated. The destructive role of the defected guiding la yers in the laser structure was shown. (C) 2000 Elsevier Science S.A. All r ights reserved.