Optical analysis of metalorganic vapor phase epitaxy grown ZnS/ZnSe/GaAs(100) heterostructures: Carrier diffusion and interface sharpness

Abstract
Metalorganic vapor phase epitaxy grown epitaxial layers of ZnS and ZnSe on GaAs(100) are investigated by Raman spectroscopy, far-infrared reflectance spectroscopy, and x-ray diffractometry. This combination allows a separate determination of crystalline quality, stress, and free carrier concentration. Furthermore, the interface sharpness can be deduced. While for optimized growth conditions the interfaces are sharp within less than 1 nm, we observe the presence of free carriers in nominally undoped epilayers. They are interpreted in terms of a diffusion of Ga atoms from the substrate into the epilayer. It is shown, that the concentration can be drastically reduced by a decrease of the growth temperature. Concentrations below 1016 cm−3 are achieved for growth at 640 K

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