Growth of GaAs Epitaxial Microcrystals on a S-terminated GaAs (001) by VLS Mechanism in MBE
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GROWTH OF GaAs EPITAXIAL MICROCRYSTALS ON S-TERMINATED GaAs (001) BY VLS MECHANISM IN MBE
NOBUYUKI KOGUCHI, KEIKO ISHIGE AND SATOSHI TAKAHASHI National Research Institute for Metals, Tsukuba Laboratories, 1-2-1 Sengen, Tsukuba, Ibaraki 305, Japan
ABSTRACT Numerous GaAs epitaxial microcrystals having nearly equal size were fabricated on a S-terminated GaAs(001) surface by a sequential supply of Ga and As molecular beams. The GaAs(001) surface was terminated by sulfur atom in the MBE chamber. The growth of GaAs epitaxial microcrystals is caused by a Vapour-Liquid-Solid(VLS) mechanism. GaAs epitaxial microcrystals were also fabricated on a S-terminated GaAIAs(001) surface by the same procedure. LINTRODUCTION We have observed a three dimensional growth of some III-V compound semiconductor epitaxial microcrystals on a II-VI compound semiconductor with a nearly equal lattice constant by a sequential supply of III and V column element molecular beams in a MBE chamber[l-31. This phenomenon is based on the V-column element incorporation into the HI-column element droplets deposited on the inert substrate for the monolayer adsorption of the III and V-column elements. This method, we termed Droplet Epitaxy, is a suitable for the fabrication of quantum well boxes. Some III-V compound surface terminated with a VI-column element like a S, Se or Te has been reported for providing an inert surface for the foreign atom adhesion caused by a partially filled dangling bond nature[4-7]. The surface of the VI-column element terminated III-V compound semiconductor is thought to be suitable for the growth of epitaxial microcrystals by Droplet Epitaxy. Indeed the GaAs epitaxial microcrystals were fabricated by this method on a S-terminated GaAs (001) surface obtained by dipping the GaAs wafer in the (NH ) Sx solution[81. But the S-termination by using this solution is not suitable for the GaAlAs surface for the GaAs-GaAIAs quantum well boxes, because the Al atom is easy to combine with oxygen atom during the termination process[6]. In this paper, we demonstrate a S-termination of the GaAs (001) and GaAIAs (001) in the MBE chamber and three dimensional growth of GaAs epitaxial microcrystals on these substrates by Droplet Epitaxy. I.EXPERIMENTAL The MBE system used in this work was a conventional system (ANELVA-620) with a sample introduction chamber. Elemental Ga, Al and As in the Knudsen cells were used as molecular beam sources. Knudsen cell with a valve in which the elemental sulfur was charged was equipped in the sample introduction chamber. The background pressure of the sample introduction chamber was 5x10- Toff. First, GaAs (001) surface was solvent cleaned by ordinary H SO solution and heated in the As molecular beam flux of beam equivalent pessule of 6x 10-6 Toff at 590 °C for 30 min to obtain a well defined (2x4) As-stabilized surface. For the S-termination of GaAs (001), the substrate temperature was decreased to the room temperature, the sample was heated again to obtain a Ga-stabilized surface to 520 °C without As molecula
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