TEM Evaluation of CuAu-I Type Ordered Structures in MBE grown Ingaas Crystals on (110) Inp Substrates
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TEM EVALUATION OF CuAu-I TYPE ORDERED STRUCTURES IN MBEGROWN InGaAs CRYSTALS ON (110) InP SUBSTRATES 0. UEDA, Y. NAKATA, T. NAKAMURA AND T. FUJII Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi 243-01, Japan ABSTRACT CuAu-I type ordered structures in InGaAs grown on (110) InP substrates by molecular beam epitaxy, have been studied by transmission electron microscopy. In the electron diffraction pattern from the InGaAs, superstructure spots associated with CuAu-I type ordered structure are found. When the tilting angle of the substrates increases, the ordering becomes stronger. The ordering is also stronger in crystals grown on substrates tilted toward the or the direction than those on substrates tilted toward the direction. From these results, one can conclude that atomic steps on the growth surface play an important role in the formation of ordered structures. The ordering becomes stronger when the growth temperature increases in the range 360-485'C. In high resolution images of the crystal, doubling in periodicity of 220 and 200 lattice fringes is found, which is associated with CuAu-I type ordered structure. Moreover, anti-phase boundaries are very often observed in the ordered regions. It is also found that ordering is not perfect, and that ordered regions are plate-like microdomains lying on planes slightly tilted from the (110) plane. INTRODUCTION Ill-V alloy semiconductors are widely used in the production of optical devices, highspeed devices and so on. In order to ensure high device performance and reliability, one must eliminate defects and control the thermal stability of the crystal. Regarding the latter point, two conflicting phenomena peculiar to these materials have been extensively studied, i.e., generation of ordered structure [1-19] and modulated structure [20-24]. Atomic ordering has been found in AlGaAs [1], In(AI)GaP [2-9], InGaAsP [10-12], InAlAs [13,14], GaAsSb [15,16], GaAsP [17,18] and InAsSb [19]. Since the ordering takes place mostly in gas-phase epitaxy, i.e., metalorganic vapor phase epitaxy (MOVPE), vapor phase epitaxy (VPE) and molecular beam epitaxy (only one exception of InGaAs crystals grown by liquid phase epitaxy (LPE) [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 [12]. In crystals grown on (001) substrates, observed ordered structure is mostly of CuPt type in which doubling in periodicity of column III or V atoms occurs on the (111) plane [2-9,11,13-19]. On the other hand, in AlGaAs crystals grown on (110) GaAs substrates by MOVPE and MBE [1], and InGaAs crystals grown on (110) InP substrates by MBE [10],CuAu-I type ordered structures have been found by Kuan et al. [1,101 by transmission electron microscopy (TEM). However, they have only shown transmission electron diffraction (TED) patterns corresponding to CuAu-I type structure, and microstrutural features of the ordered regions and dependence on growth conditions of the degree of ordering have not been
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