Surface Ordering of MBE Grown 001 Ga
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Surface Ordering of MBE Grown 001 Gal__Al1As-'A Theoretical Study Rita Trivedi and R. Venkatasubramanian Department of Electrical and Computer Engineering University of Nevada, Las Vegas Abstract The kinetics of MBE growth of Gal-.,Al.,As is studied theoretically using the stochastic model of MBE growth based on the master equation approach and the random distribution approximation. The surface ordering phenomenon during the 001 growth of Ga0 .5 A! 0 ,5 As is investigated as a function of the growth conditions. The atom pair interaction energy parameters for various surface configurations were obtained from the first principle calculations. The other model parameters needed in the description of the kinetic processes are obtained from the available experimental data. The ordering kinetics is studied as a function of fluxes, flux ratio and growth temperature. The degree of ordering is estimated in terms of the short range order parameter. The short range order parameter increases with temperature till 650°K and 750'K for cation to anion flux ratios 2 : 1 and 1 : 5, respectively. Beyond this critical temperature, the short range order parameter decreases. This critical temperature is identified as the kinetic order-disorder temperature. The order-disorder phenomenon observed in this theoretical study is explained in terms of the dependence of the surface migration rate of the cations on the growth temperature. The dependence on the order-disorder temperature on the flux ratio is attributed to decreased surface migration for larger flux ratios.
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Introduction
Presence of long range ordering in the as grown epilayers reduces the band gap of the materials and thus has implications in the device applications. Long range order has been observed in many compound semiconductors grown by MBE and MOCVD [1-6]. A few of the compound semiconductors which exhibit long range order in as grown samples are: GaAlAs, GaAsSb, InAsSb, GaInAs and GaInAsP. The presence of ordering in the epilayers is usually observed using transmission electron microscopy (TEM). The ordering observed in these compounds is shown to be growth and surface conditions and orientation dependent. For example, in MBE grown Ga_,_A,,lAs, it was observed that the degree of ordering as observed in terms of the intensity of superstructure reflections in TEM observations, depends on the substrate orientation, growth temperature and the Al content. The epitaxial strain between substrate and the epilayer is also shown to play a role in deciding the type and degree of ordering [6], In this manuscript, the stochastic model approach developed for the study of the MBE growth of compound semiconductors [9,10] is employed to study the MBE surface ordering kinetics in Gai_.AlAs. In section 2, a brief discussion of the stochastic model for the MBE alloying studies is presented. The results of the surface ordering kinetic study of Gal_.,AlAs along with a discussion of the results is presented in section 3. Conclusions of this study are stated in section 4.
Mat. Res. Soc. Symp
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