Temperature Dependence of Morphology of INP Films Grown by Metalorganic Molecular Beam Epitaxy
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( 1)Unicamp, IFGW/DFA, CP 6165, 13081 Campinas SP, Brazil (2)AT&T Bell Laboratories, Murray Hill, NJ 07974 3 ( )Colorado State University, Fort Collins, CO 80523
ABSTRACT
Two regimes of growth are observed for epitaxial films of InP prepared by metalorganic molecular beam epitaxy. Below a minimum growth temperature, T"", kinetic roughening is observed. At temperatures higher than Tr", smooth morphologies are obtained. From the dependence of , on the substrate misorientation, we estimate a value of -0.4-0.5eV for the Schwoebel barrier. At growth temperatures higher than T"in we observe two types of defects: large oval defects related only to the initial conditions of the substrate surface and small defects with the density strongly dependent on the growth condition. Increasing temperature above Trainor decreasing V/IIl ratio, results in increased density of these defects. In addition, their density increases with an activation energy that depends on the substrate misorientation. The origin of the oval defects is attributed to non-stoichiometric, P-defficient, clusters on the growing surface, formed either by enhanced cracking of metalorganics on the substrate due to the presence of contaminants or by a low V/III ratio used for growth. INTRODUCTION
We investigate the temperature dependence of InP films by metalorganic molecular beam epitaxy (MOMBE). We show that below a minimum growth temperature, Tmin kinetic roughening occurs. This temperature depends strongly on group III and V fluxes and the misorientation of the substrate used. At temperatures higher than Tg , smooth morphologies and flat interfaces are obtained. From the dependence of T" on the substrate misorientation we are able to estimate the magnitude of the Schwoebel barrier. This barrier, which we estimate at -0.4 -0.5eV, is believed to be responsible for kinetic roughening of epitaxially grown layers. At the growth conditions resulting in smooth films, i.e. above T", we observe surface defects. The large defects are similar to the well known oval defects extensively studied in MBE grown films of GaAs. Their formation has been attributed to the substrate preparation [1] and to the Ga effusion cell problems (2,31. MOMBE uses no solid sources and thus could be considered largely immune from this problem. Such defects, however, have been reported in InP films grown by this technique [4,5]. We show here that the density of the oval defects is independent of the growth condition and can be largely eliminated by the proper preparation of the substrate surface. At growth temperatures well above Tnin and decreased V/III ratios we g observe smaller size defects. Their density depends on the growth conditions and increases with 123 Mat. Res. Soc. Symp. Proc. Vol. 317. ©1994 Materials Research Society
an activation energy that depends on the substrate misorientation. This indicates P defficiency as the likely origin of the small (stoichiometric) defects.
EXPERIMENTAL RESULTS AND DISCUSSION The InP epitaxial layers were grown on InP substrates with differen
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