Abstract

Many optical and optoelectronic device properties depend on the precise control of the composition and thickness of the layers and on the abruptness of compositional steps. Properly designed gas delivery systems in OM-VPE reactors can achieve abrupt steps in gas composition, but not necessarily in the solid material of the epilayers. We have observed composition gradients at the interfaces, during OM-VPE deposition of Al_xGa_1-xAs, by in situ optical reflection and postdeposition spectrophotometry. A depth profile of the composition was measured by sputtering SIMS and it was compared to the profile obtained by the analysis of in situ reflectance and spectral data. This work demonstrates the presence of compositional gradients in OM-VPE-grown materials, even when the gas-delivery system is designed to achieve abrupt steps in gas composition. Possible mechanisms for the formation of gradients, techniques to achieve abrupt composition steps in the layers, and the usefulness of in situ techniques to characterize the OM-VPE deposition of semiconductors will be discussed.

© 1990 Optical Society of America