A secondary ion mass spectrometry investigation was made of Be diffusion, during the molecular beam epitaxial growth of graded-index separate confinement heterostructure laser structures. In the case of growth at 700C, it was found that Be from the p-type AlGaAs cladding layer diffused into the quantum well and beyond. As a result, the p-n junction was displaced from the heterojunction. The extent of Be diffusion was found to depend upon the dopants in the graded-index regions which adjoined the GaAs active layer. When the graded-index segments were left undoped, Be diffused through the entire p-side graded-index region, the quantum well active region, and a significant portion of the n-side graded-index region. However, when the graded-index regions were doped with Be and Si on the p-side and n-side, respectively, the displacement of the p-n junction which was caused by Be diffusion was significantly reduced. Upon assuming that Be diffused from a constant surface source and into an n-type layer, as a singly charged interstitial donor, the present analysis predicted that increasing the doping of the n-type layer would retard Be diffusion; whereas increasing the doping of the p-type layer would enhance it. Upon including the electric field of the p-n junction in the model, peaks and inflections were predicted which resembled those that were observed in experimental secondary ion mass spectroscopy profiles. It was concluded that, because of Be-related O contamination and Be diffusion in the p-side graded-index region, the presence of Be should be avoided on the p side. However, Si additions to the n side were expected to be beneficial as they minimized Be diffusion and p-n junction displacement.

Silicon-Doping Level Dependent Diffusion of Be in AlGaAs/GaAs Quantum Well Lasers. V.Swaminathan, N.Chand, M.Geva, P.J.Anthony, A.S.Jordan: Journal of Applied Physics, 1992, 72[10], 4648-54