The Influence of Initial Growth on Defect Generation in MOCVD Grown GaAs/Si Heteroepitaxial Layers
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THE INFLUENCE OF INITIAL GROWTH ON DEFECT GENERATION IN MOCVD GROWN GaAs/Si HETEROEPITAXIAL LAYERS T. George, E.R. Weber Dept. of Materials Science and Mineral Engineering, University of California, Berkeley, CA 94720 S. Nozaki, A.T. Wu Intel Corporation, Santa Clara, CA 95052 M. Umeno Nagoya Institute of Technology, Nagoya, Japan ABSTRACT The structural quality of GaAs/Si layers deposited directly at the normal growth temperatures (650°C,750°C) is compared with that of layers grown by the standard two-step growth process using Metalorganic Chemical Vapor Deposition (MOCVD). The directly grown layers are highly twinned and polycrystalline in nature whereas the two step growth process produces single crystal layers even at growth temperatures as high as 800°C. The origin of these effects is related to the initial growth of the GaAs, which is in the form of highly defective separate islands, for the case of direct growth, and connected single crystal islands for the case of two-step growth. The directly grown islands exhibit a "ripening" type behavior, with a strong dependence of the Si substrate surface coverage by the GaAs layer, on the growth temperature. The generation of structural defects such as stacking faults and microtwins, which destroy the epitaxial relationship could be triggered by the presence of surface imperfections on the Si substrate. INTRODUCTION GaAs on Si heteroepitaxy has gained importance during the past few years, since it offers the possibility of combining specialized GaAs optoelectronic and high speed devices with state of the art Si VLSI (Very Large Scale Integrated Circuits). The presence of high densities of structural defects in the GaAs/Si films has been a major cause for concern, since these could be a reason for the poor performance of devices such as laser diodes that are fabricated using these layers. The growth of high quality heteroepitaxial films of GaAs on Si is complicated by several factors: the large lattice constant mismatch (4%), polar/non polar effects and Si substrate cleanliness. These factors prevented the production of single crystal GaAs/Si films in the early stages of research into GaAs/Si heteroepitaxy. An empirical approach to overcome this problem was proposed by Akiyama et al [ 1] where the GaAs layer is grown in two steps by MOCVD, the first step being the growth of a thin layer (- 125A) at a low temperature (400'C) followed by further growth at the standard growth temperatures for GaAs epitaxy. This "two-step" growth process has become very popular as a means to produce single crystal GaAs/Si layers. In the present work, the growth process is examined in depth, with the view of understanding the nucleation behavior and the generation of structural defects in GaAs/Si layers. A comparison is made between the structural quality of GaAs/Si layers grown directly at the normal growth temperature with that of layers grown by the two-step process.
Mat. Res. Soc. Symp. Proc. Vol. 198. c1990 Materials Research Society
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EXPERIMENTAL DETAILS The GaAs/Si heteroepit
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