Single Crystalline Germanium Island on Silicon Dioxide by Zone Melting
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SINGLE CRYSTALLINE GERMANIUM ISLAND ON SILICON DIOXIDE BY ZONE MELTING M. TAKAI, T. TANIGAWA, K. GAMO, Faculty of Engineering Science, Toyonaka, Osaka 560, JAPAN
and S. NAMBA Osaka University
ABSTRACT Single crystalline germanium islands on Si0 2 have been formed by zone melting with graphite strip heaters. Two types of geometrical patterns for islands were successfully used to obtain large single crystalline islands. Most germanium islands were found to be single crystal and the predominant orientation was (100). Electron concentrations of 1016 - 1018 /cm 3 with Hall mobility of 3 x 103 - 1 x lO3 cm 2 /Vsec were obtained for single crystalline germanium islands. Gallium Arsenide layers, grown by molecular beam epitaxy, on the germanium islands were found to emit photoluminescence, the intensity of which was almost comparable to that of gallium arsenide layers on bulk germanium crystals. INTRODUCTION Extensive studies on single crystalline silicon-on-insulator (SOI) structures by various techniques such as zone-melting with graphite strip heaters, laser and electron beam recrystallization have recently been made because of the potential for application in thin film transistors for flat panel display devices or for realizing three dimensional integrated circuits [1]. Single crystalline germanium (Ge) formation on insulator, on the other hand, has not been studied much [2], though this structure is useful for an interface layer of gallium arsenide (GaAs) epitaxy on insulator, in which hybrid integrated circuits including optical functions will be realized. Recrystallization techniques such as zone melting using strip heaters or electron beams have been investigated since the 1960's [3-5]. It was, however, only recently that these techniques drew attention because of technological need for application and intensive studies by laser and electron beams. Zone melting recrystallization can provide a larger grain size in comparison with laser recrystallization [6]. However, it is necessary to use well defined geometrical patterns to control grain sizes and locations [7,8]. In this study, single crystalline Ge islands were formed on silicon dioxide by zone-melting using graphite strip heaters in order to provide an interfacelayer for GaAs epitaxy. Two types of geometrical island patterns were successfully used, so that large single crystalline islands could be obtained. Optical, transmission electron microscopies and Hall effect mreasurements were performed to characterize isolated Ge islands. GaAs layers were grown by molecular beam epitaxy (MBE) on the obtained Ge islands. Photoluminescence (PL) measurements were performed to characterize GaAs layers on the Ge islands. EXPERIMENTAL PROCEDURES Ge layers with a thickness of 700 - 1000 nm were deposited on (100) Si wafers with a 730 nm thick thermal oxide at a substrate temperature of 400 0 C by evaporating Ge ingots ( 99.999 %). The vacuum during Ge deposition was Mat. Res.Soc. Symp. Proc. Vol. 23 (1984) OElsevier science Publishing Co., Inc.
398
10-6 Torr. The deposit
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