Beryllium diffusion in short-period AlxGa1 − xAs/AlAs-superlattices and vertically compact laser structures grown by molecular beam epitaxy

Dopant diffusion is investigated by depth profiling with secondary ion mass spectrometry (SIMS) in heterostructures containing Be-doped short-period superlattice AlxGa1 − xAs layers (0.3 ⩽x⩽0.8) grown by molecular beam epitaxy. At a Be concentration of 2×1018 cm− 3 we observe Be outdiffusion into the undoped GaAs layers only at a substrate temperature of 660 °C. At a doping concentration of 2×1019 cm− 3 a strong increase in diffusion occurs for all growth temperatures. Depth profiles show solubility limits for Be of 1×1019 cm− 3 at x=0.6 and 2×1018 cm− 3 at x=0.8 in AlxGa1 − xAs layers. Lasers were fabricated with different p-cladding thickness of 450 and 600 nm. An increased threshold current is observed for the structure with the thinner cladding. SIMS depth profiles show that the amount of diffused Be into the active region was about two times higher in the sample with the thin cladding layer. Therefore, we attribute the increase of the threshold current to the enhanced Be diffusion from the part of the p-cladding layer with highest doping concentration and from the heavily-doped graded layer since in both layers the solubility limits were exceeded.