Comparison of Ordered and Modulated Structures in InGaP Alloy Semiconductors grown by MOCVD, Chloride-Vpe and LPE Method
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COMPARISON OF ORDERED AND MODULATED STRUCTURES IN InGaP ALLOY SEMICONDUCTORS GROWN BY MOCVD, CHLORIDE-VPE AND LPE METHODS 0 UEDA , T. KATO *, T. MATSUMOTO**, M. HOSHINO , M.. TAKECHI*. AND M. OZEKI **Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi 243-01, Japan Yamanashi University, 4-3-11 Takeda, Kofu 400, Japan ABSTRACT Ordered and modulated structures in InGaP alloy semiconductors grown on (001) GaAs substrates by metalorganic chemical vapor deposition, chloridevapor phase epitaxy, and liquid phase epitaxy have been systematically In InGaP grown by studied by transmission electron microscopy. metalorganic chemical vapor deposition at 630 0 C, strong ordering of CuPttype has been observed, which is associated with an abnormality in the photoluminescence peak energy. For crystals grown by chloride-vapor phase epitaxy, CuPt-type ordered structures have also been observed. However, the degree of ordering is weaker in the latter case and crystals grown at 0 576-740 C exhibit normal photoluminescence peak energies. On the other hand, in crystals grown by liquid phase epitaxy, no superstructure spots are found in the electron diffraction patterns and the crystals exhibit normal photoluminescence peak energies. Modulated structures do not depend on the growth method since they are observed in all crystals. From these results, it has been concluded that the ordered structures are not generated under thermal equilibrium conditions but rather by the diffusion and reconstruction of deposited atoms on the growth surface. INTRODUCTION III-V alloy semiconductors are widely used in the production of optical devices, high-speed devices and so on. To ensure high device performance and reliability, one must eliminate defects and control the thermal stability of the crystal. Regarding the latter point, two phenomena peculiar to these materials have been extensively studied, i.e., generation of ordered structurefl-19] and modulated structure[20-24]. Atomic ordering has been found in AlGaAs[l], In(Al)GaP[2-9], InGaAs(P)[lO-12], InAlAsfl3,141, GaAsSb[15,161, GaAsP[17,18], and InAsSb[19]. Since the ordering takes place mostly in gas-phase epitaxy, i.e., MOCVD, VPE, and MBE (only one exception of LPE-InGaAs[12]), it is believed that this phenomenon is strongly related to growth kinetics, i.e., migration and reconstruction of deposited atoms on the growth surface[2,7]. However, because of the lack of the direct evidence for the non-existence of ordered structures in most alloy semiconductors grown by LPE, this speculation has not been proved yet. In this paper, we describe a detailed TEM study on the ordered and modulated structures in InGaP crystals grown by MOCVD, Chloride-VPE, and LPE, and we conclude for the first time that atomic ordering is only associated with growth kinetics and that it is not a bulk phenomenon. EXPERIMENTAL PROCEDURES In this study, undoped-InGaP crystals grown by three different growth methods, MOCVD,chloride-VPE(C-VPE)., and LPE, were investigated. In the case of MOCVD, crystals are grown on (001)
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