Origin of Defects in MOCVD Growth of GaP on Silicon
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ORIGIN OF DEFECTS IN MOCVD GROWTH OF GaP ON SILICON
A.E. BLAKESLEE, M.M. AL-JASSIM and S.E. ASHER Solar Energy Research Institute, Golden, CO 80401.
ABSTRACT We have studied the nucleation, annealing and growth of GaP on Si Our findings are very similar to those reported for GaAs4Si. substrates. That is, dislocation density after I pm of growth is usually about 108 cm-2 surface morphology is best when a multi-temperature growth process is used and is dependent on the substrate orientation; antiphase domain density is This commonality of results leads minimized by misorienting the substrates. us to conclude that the elimination of interfacial contamination is more important in achieving good epitaxial growth of III-V compounds on Si than is In support of this hypothesis we present the overcoming of lattice mismatch. SIMS data revealing up to 2% of interfacial carbon and TEM observations of an The carbon comes from the organometallic source amorphous interfacial phase. and, we believe, reacts with the Si to form amorphous SiC, which disrupts the coalescence of GaP grains and produces lattice defects.
INTRODUCTION Extensive research has been devoted in the past few years toward realization of a new optoelectronic technology based on III-V compound films The proceedings of the 1986 MRS deposited by MBE or MOCVD on Si substrates. Spring Meeting [I] describe a large portion of this research, but these and other reports [2] are devoted almost entirely to the growth of GaAs on Si; Our interest in this latter pair little is said about the combination GaP/Si. of semiconductors is sparked by our program to build a cascade solar cell in which GaAs. 7 P. 3 constitutes the high bandgap top cell and Si serves as hoth GaP provides the transition between the substrate and the bottom cell [3]. It was thought initially that the near lattice matching the two cell areas. of GaP and Si---ao = 5.431 A for Si and 5.449 A for GaP---would be a major However, it now appears that advantage in fabricating this complex structure. this view is oversimplified and that other factors, notably thermal expansion, chemical compatibility, and interfacial contamination, are equally important The mechanical, optical, and electrical coupling of the III-V or more so. compounds to the Si through the layer of GaP has presented a variety of challenges in the area of materials growth. The work described here is a continuation of that reported earlier by Olson et al. [4]. One of their important findings was that, for the MOCVD growth of GaP on Si, a two-temperature growth process produced films which were smoother and contained less structural defects than when growth was Their observation is similar to those of carried out at a single temperature. several authors for growth of GaAs on Si [5-7], in which best results were obtained when a layer only a few hundred A thick was nucleated at a low temperature and the main body of the film was grown in a second highBecause this runs counter to the fact that crystals temperature stage. generally grow more readily,
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