Document Type

Conference Proceeding

Publication Title

Proceedings of SPIE - the International Society for Optical Engineering


Homogeneous II-VI narrow gap semiconducting alloys are of interest because of their use in infrared detectors. These compound semiconductor materials are inherently difficult to grow in bulk due to gravity induced convective flows. A microgravity growth environment has therefore been considered. In order to evaluate the quality of crystals grown in space compared to those grown on the ground, it is necessary to characterize both. One important aspect of this characterization is the study of stoichiometry, x. A characterization scheme using scanning tunneling optical spectroscopy (STOS) involves determining the spectral response of the photoexcited tunneling current for a semiconductor. By measuring the photoenhanced tunneling current versus photon energy, the band gap Eg of the semiconductor material can be determined. Such measurements determine Eg equals Eg(x) locally, and thus x can be determined as a function of position provided Eg(x) is known. We consider a one dimensional model, involving a simple analysis of absorption of photons, production of photoelectrons, diffusion of photoelectrons to the surface, and tunneling of these electrons to the STM probe. Our results of photoenhanced tunneling current versus photon energy are qualitatively similar to experiment. After our results are presented, we list questions that need to be considered for an improved version of our analysis which is planned.



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