An investigation was made of thermally-induced interdiffusion in quantum wells, and of the out-diffusion of Ga atoms from the GaAs substrate, by using photoluminescence, secondary-ion mass spectrometry and contactless electroreflectance spectroscopic techniques. The quantum-well structures, grown by molecular beam epitaxy, were annealed at temperatures of between 250 and 700C. The 15K photoluminescence main peak disappeared, when the annealing temperature exceeded 550C, from samples which had been grown with a 0.1μ ZnSe buffer (sample A). The photoluminescence main peak disappeared, when the annealing temperature exceeded 600C, from samples which were grown with a 0.85μ ZnS buffer (sample C). In sample A, two extra photoluminescence peaks at around 2.0 and 2.3eV were observed when the annealing temperature exceeded 500C. Such peaks were observed for sample C only when the annealing temperature reached 700C. Secondary-ion mass spectrometry revealed the interdiffusion of Cd in the ZnCdSe/ZnSe quantum-well regions in both samples. However, only sample A exhibited marked out-diffusion of Ga from the substrate, into the epilayer side. It was weaker in sample C. The main peaks of the photoluminescence spectra and the inter sub-band transitions in contactless electroreflectance spectra disappeared due to Cd interdiffusion in the wells and to defect-related transitions which were introduced by Ga out-diffusion into the epilayer side. It was concluded that a thicker ZnS buffer layer could increase the thermal stability of ZnCdSe/ZnSe quantum-wells on GaAs substrates because of its effectiveness in initiating out-diffusion of Ga into buffer layers and the interdiffusion of quantum-well regions.

Annealing effects on ZnCdSe/ZnSe quantum wells and ZnSe/GaAs interfaces R.C.Tu, Y.K.Su, Y.S.Huang, S.T.Chou: Journal of Applied Physics, 1998, 84[11], 6017-22