Interface Formation and the Heteroepitaxy of ZnSe on Si
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INTERFACE FORMATION AND THE HETEROEPITAXY OF ZnSe ON Si.
R. D.BRINGANS, D. K.BIEGELSEN, F.A. PONCE, L.-E. SWARTZ and J. C.TRAMONTANA Xerox Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, CA 94304
ABSTRACT Zinc selenide films have been grown heteroepitaxially on Si(100) substrates by molecular beam epitaxy. The growth has been carried out for raised substrate temperatures and also at room temperature followed by solid-phase epitaxial (SPE) regrowth. The ZnSe films have been characterized by a number of surface-sensitive techniques and both the interface and the bulk material have been examined with high resolution transmission electron microscopy (HRTEM). We find that an interlayer, which is most likely SiSex, is present between the ZnSe film and the Si 0 substrate for growths made at 300 C and causes loss of epitaxy. In the case of room temperature deposition and SPE, it is absent, leading to good epitaxy. In the latter situation, the films are very
uniform and there is a 40 rotation of the ZnSe crystal axes relative to those of the Si substrate. INTRODUCTION The heteroepitaxy of III-V and II-VI compounds on silicon raises a number of important issues. The interface between polar and non-polar materials is frequently not atomically abrupt and intermixing over several atomic layers can take place. Our previous studies of ZnSe films of a few monolayers in thickness grown on Si showed that Se atoms reacted with the Si substrate and that island formation may take place at the early stages of growth[1]. In the present paper we describe results for thicker ZnSe films. We have found that films deposited at room temperature and then annealed to allow solid phase epitaxy (SPE) to take place are single crystal and uniform in thickness. ZnSe films deposited at raised temperatures, on the other hand, appear to react with the silicon substrate. This leads to a thick amorphous layer on top of the substrate and to a polycrystalline ZnSe layer. Because ZnSe-on-Si has the same lattice mismatch (4%) as GaAs-on-Si but significantly different chemistry, the implications of the present results for GaAs on Si epitaxy will be discussed. EXPERIMENTAL DETAILS The silicon wafers used as substrates had their surfaces tilted by 4 degrees from the (100) plane (the surface normal being tilted by 4 degrees towards [0-11)). A thin, protective oxide was grown on these (0.01 ohm-cm, n-type) silicon substrates as described elsewhere [2].
After
introduction into ultra high vacuum, the oxide was thermally desorbed and the surface cleanliness and order was determined by x-ray photoemission (XPS) or Auger spectroscopy (AES) and low energy electron diffraction (LEED). The ZnSe and GaAs films were grown in situ by molecular beam epitaxy (MBE), using a compound ZnSe source and elemental As and Ga sources, respectively. Mat. Res. Soc. Symp. Proc. Vol. 198. @1990 Materials Research Society
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Growth rates were close to 0.1 nm per second. The resulting films were characterized in situ with AES, XPS and LEED. Prior to standard sample thin
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