SILICON-DOPING LEVEL DEPENDENT DIFFUSION OF BE IN ALGAAS/GAAS QUANTUM-WELL LASERS

We have investigated Be diffusion during molecular beam epitaxial growth of GaAs/AlGaAs graded index separate confinement heterostructure laser structures using secondary ion mass spectrometry (SIMS). For growth at 700-degrees-C we find that Be from the p-type AlGaAs cladding layer diffuses into the quantum well and beyond. As a result, the p-n junction is displaced from the heterojunction. The extent of Be diffusion is found to depend on the dopants in the graded index (GRIN) regions adjoining the GaAs active layer. When the GRIN segments are left intentionally undoped, Be diffuses through the entire p-side GRIN, the quantum well active and a significant portion of the n-side GRIN. However, when the GRIN regions are doped, respectively, with Be and Si on the p and n sides, the displacement of the p-n junction caused by Be diffusion is significantly reduced. Assuming that Be diffuses from a constant source at the surface into a n-type layer as a singly charged interstitial donor, our analysis predicts that increasing the doping of the n layer retards the diffusion of Be while that of the p layer enhances it. Further, including the electric field of the p-n junction in the model leads to peaks and inflections resembling those observed in the experimental SIMS profiles. In view of Be-related oxygen contamination and Be diffusion on the p-side GRIN region, Be should be dispensed with on the p side, however, Si addition on the n side is beneficial as it minimizes Be diffusion and p-n junction displacement.