Growth of CuInSe 2 on (100)GaAs by Molecular Beam Epitaxy
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ABSTRACT Domain-free epitaxial layer of CuInSe2 has been successfully grown on (100)GaAs at the substrate temperature above 4706C. Both TEM and X-ray analyses were performed to verify this result. The CuInSe/GaAs interface was examined by high resolution TEM. For films high in indium, InSe was identifed by X-ray diffraction. TEM observations showed that the InSe precipitates were rectangular in shape and the habit plane was determined to be (110). Photo-assisted MBE technique had also been used for the growth of CuInSe 2 films with high crystalline quality. The epitaxial temperature was significantly reduced to 300'C.
INTRODUCTION CuInSe 2 is the only I-III-V12 compound under intensive study because of its high potential in solar-cell applications [1-3]. The solar conversion efficiency has been pushed to a record-high 18.6% this year [4]. In contrast to the research in solar-cell area, there are few research activities on other device applications such as light emitting devices, superlattice devices,..., etc. The precise control of material compositions and properties is probably the largest obstacle to device developments. Therefore, we use the molecular beam epitaxy (MBE) technique to grow CuInSe 2 epitaxially on GaAs substrate. In this paper, our emphasis are on the study of interfacial structure and domain structure of CuInSe 2 epitaxial layer. Although a few papers about epitaxial growth has been published by other groups, none of these topics have been addressed [5-7]. Moreover, photo-assisted MBE technique is applied for the growth of thin films in order to lower the epitaxial temperature. It is expected to lower the intrinsic defect concentrations in the films and minimize interdiffusion and mismatch in thermal expansion between CuInSe 2 and GaAs. EXPERIMENTAL PROCEDURES Thin films of CuInSe 2 were grown by molecular beam deposition. The background pressure of the deposition system was 4 x 10' torr after bakeout. The temperature of Cu source and Se source was kept at 1050'C and 210'C, respectively. The temperature of In source was varied from 720°C to 750'C in order to control the Cu/In ratio of the films. The substrate was heated by quartz lamps and the temperature was measured by a thermocouple attached near to the substrate. The temperatures of elemental sources and substrate were controlled by Eurotherm 818S controllers and the temperature variations were within IVC. An Oriel Photomax 200W Hg lamp was used for the photo-assisted growth. All films were grown on (100)GaAs substrates. The crystallinity of the films was evaluated by X-ray diffractometer(XRD) and transmission electron microscope(TEM). The interfacial structures were revealed by the high resolution 187 Mat. Res. Soc. Symp. Proc. Vol. 317. @1994 Materials Research Society
TEM. The TEM specimens were prepared by ion millng. A liquid-nitrogen-cooled stage was used to prevent the damage caused by ion bombardment. Electron microprobe was used to measure chemical compositions of thin films. A standard was used to calibrate the WDX system to perm
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