BERYLLIUM DIFFUSION IN SHORT-PERIOD ALXGA1-XAS ALAS-SUPERLATTICES ANDVERTICALLY 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 shor t-period superlattice AlxGa1-xAs layers (0.3 less than or equal to x l ess than or equal to 0.8) grown by molecular beam epitaxy. At a Be con centration of 2 x 10(18) cm(-3) we observe Be outdiffusion into the un doped GaAs layers only at a substrate temperature of 660 degrees C. At a doping concentration of 2 x 10(19) cm(-3) a strong increase in diff usion occurs for all growth temperatures. Depth profiles show solubili ty limits for Be of 1 x 10(19) cm(-3) at x = 0.6 and 2 x 10(18) cm(-3) at x = 0.8 in AlxGa1-xAs layers. Lasers were fabricated with differen t p-cladding thickness of 450 and 600 nm. An increased threshold curre nt is observed for the structure with the thinner cladding. SIMS depth profiles show that the amount of diffused Be into the active region w as about two times higher in the sample with the thin cladding layer. Therefore, we attribute the increase of the threshold current to the e nhanced Be diffusion from the part of the p-cladding layer with highes t doping concentration and from the heavily-doped graded layer since i n both layers the solubility limits were exceeded. (C) 1997 Elsevier S cience S.A.