We have used electrolyte electroreflectance (EER) to characterize ZnSe/GaAs and ZnSe/AlAs interfaces. The great sensitivity of EER to interface space-charge regions enabled us to detect both interface crossover transitions and transitions to triangular-well interface states. The observation of these transitions provides the first unambiguous proof that the ZnSe/GaAs interface is type I and allowed us to determine the band offsets and band bendings, the diffusion lengths across each interface, and the amount of interdiffusion.

We report the results of optical and electrical measurements performed on two pseudomorphic ZnSe/n+GaAs heterojunctions in which the ZnSe was grown by molecular beam epitaxy. One of t h e ZnSe epilayers was doped as a p-n junction using Li and CI as dopants, with t h e layer adjacent to the interface doped n + ; the other was unintentionally doped. Our results determine uniquely the band profiles of both samples studied. Those band profiles clearly display t h e effects of Zn and Ga interdiffusion, which creates strong band-bending on both sides of the interlaces and creates in the GaAs a barrier against electron diffusion into t h e ZnSe. T h e presence and size of that barrier is of primary importance for ail ZnSeIGaAs device considerations. For each sample our measurements determine the height and depth of that barrier, the position of the bands at the interface relative to the Fermi level, and t h e built-in field on each side of the interface. From that information the magnitude and range of the Zn and Ga interdiflusion are determined.

Electrolyte electroreflectance (EER) is used to investigate the interface between undoped ZnSe and heavily n-doped GaAs. The evolution of t h e signal with bias allows an identification of the various features in the EER spectra. The spectra allow u s to determine the band profile of t h e heterojunction, which consists of 100 nm of unintentionally doped ZnSe grown by molecular beam epitaxy on n+GaAs:Si. The band profile that we obtain differs from previously proposed models for the band profile, but explains the transport results that motivated those models. In particular, due to the interdiffusion of Zn and Ga atoms, it displays a strongly p-type region in the GaAs near the interface and an n-type region extending of the order of 5 n m into the ZnSe from the interface.

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KOH, an anisotropic etchant of monocrystalline Si, may cause roughness and defects whose shapes are related to crystallographic orientations. This paper studies the effect of processing steps on the formation of geometric etch defects. Implantation, thermal treatment, epitaxial growth or photoresist were not the source of such defects. In the scope of this study, only unwanted damage caused geometric etch defects. This makes the observation of the wafer after KOH etch a good indicator of the quality of previous steps.

Band profiles specify the position of all band edges as a function of distance from a sample surface or interface. They largely determine the electrical and optoelectronic properties of semiconductor heterostructures. Neither theory nor standard transport measurements alone have been able to give reliable values for band offsets, much less entire band profiles. However, the use of electroreflectance, which reveals crossover transitions between localized states or band edges present on opposite sides of an interface, and which allows us to measure accurately built-in fields, has allowed us to determine accurate band profiles for several types of semiconductor heterostructures. The procedure used to find the band profile is elucidated in detail for two technologically important cases.

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