Characterization of CdTe thin films grown on glass by hot wall epitaxy

Abstract

In this work we have investigated the properties of CdTe thin films grown on glass substrates by Hot Wall Epitaxy. Its most important feature is the growth at very low temperatures, which would allow the growth even on polymer substrates. Our samples were grown at temperatures between 150 and 250 o C at a growth rate between 0.2 and 2 µm/h. The CdTe films were characterized by x-ray diffraction, scanning electron microscopy and optical transmission. The x-ray teta-2teta scans revealed films with cubic structure and a very high degree of preferential orientation. In fact, for films thicker than 1 µm, no other reflections have been observed on the spectra besides the (111), (333) The production of CdTe thin films has been investigated for many years. The semiconductor properties of this material are suitable for application in solar cells and many other optoelectronic devices such as detectors for the infrared and x-rayThe most used techniques to obtain these films are organometalic chemical vapour deposition [5], closed spaced sublimation [6], physical vapour deposition [7], molecular beam epitaxy [8], electrodeposition [9] and sputtering [10]. All these techniques have advantages and disadvantages depending on the type of application intended for the film. Parameters such as range of deposition temperatures and growth rates obtained, type of substrates used and films produced (epitaxial or polycrystalline) must all be of concern.In this work we describe the production and characterization of CdTe thin films grown on glass substrates. The growth technique used was the Hot Wall Epitaxy (HWE) and the films were characterized by scanning electron micrographs, atomic force microscopy (AFM), x-ray diffraction and optical transmission in the visible and near infrared. I. EXPERIMENTALThe HWE growth system used is shown in Fig. 1. It consists of a two furnace system, for source and substrate, separated by a shutter. The deposition occurs at pressures between 10 −6 and 10 −7 Torr, obtained by a diffusion pump.High purity commercial CdTe (99.999%) was used as source material and the source temperature can be controlled from 400 to 590 o C. In this temperature range CdTe evaporates congruently with more than 98% of CdTe molecules in the vapor. The growth rates obtained were in the range between 0.01 and 10Å/s. In this work we have used growth rates between 0.5 and 5.5Å/s.The HWE is a well established technique able to produce † Laboratório Associado de Sensores e Materiais, Instituto Nacional de Pesquisas Espaciais, Caixa Postal 515, 12245-970 São José dos Campos-SP, Brazil Received on , 2003In this work we have investigated the properties of CdTe thin films grown on glass substrates by Hot Wall Epitaxy. Its most important feature is the growth at very low temperatures, which would allow the growth even on polymer substrates. Our samples were grown at temperatures between 150 and 250 o C at a growth rate between 0.2 and 2 m/h. The CdTe films were characterized by xray diffraction, scanning electron microscopy and optical t...

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