Indium incorporation and surface segregation during InGaN growth by molecular beam epitaxy
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Indium incorporation and surface segregation during InGaN growth by molecular beam epitaxy Huajie Chen1,1 R. M. Feenstra1, J. E. Northrup2, J. Neugebauer3, and D. W. Greve4 1 Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 2Xerox Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, California 94304 3Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany 4Department of Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 ABSTRACT InGaN alloys with (0001) or (000 1 ) polarities are grown by plasma-assisted molecular beam epitaxy. Scanning tunneling microscopy images, interpreted using first-principles theoretical calculations, show that there is strong indium surface segregation on InGaN for both (0001) and (000 1 ) polarities. The dependence on growth temperature and group III/V ratio of indium incorporation in InGaN is reported, and a model based on indium surface segregation is proposed to explain the observations. INTRODUCTION Ternary InxGa1-xN alloys are used as the active layer in GaN-based light emitting diodes (LEDs) and lasers [1]. It is thus important to understand and control the growth of InGaN. In our earlier work [2] we studied the dependence of In incorporation on growth parameters for InGaN with (000 1 ) polarity. A qualitative model for the indium incorporation was proposed, based on observed strong surface segregation of the indium. In this paper, results for the dependence of indium incorporation on growth parameters are given for InGaN with (0001) polarity. It is found that the incorporation decreases when the growth temperature is increased, it decreases when the group III/ group V flux ratio is increased under metal rich conditions, and it increases as a function of this flux ratio under nitrogen rich conditions. A quantitative model is proposed to explain this dependence. The basic InGaN surface structures discussed here are illustrated in Fig. 1. Figure 1(a) shows the previously determined structure for the InGaN(000 1 ) surface, consisting of a monolayer (ML) of indium bonded to a GaN bilayer [2]. For less In-rich conditions this monolayer contains a mixture of indium and Ga. For the InGaN(0001) surface, prior theoretical studies indicate that the surface consists of two monolayers of metal atoms, with the top layer being entirely indium atoms, and the second layer containing a mixture of indium and Ga atoms [3,4]. This structure is illustrated in Fig. 1(b). Figure 1 Basic structure of InGaN surfaces: (a) (000 1 ), surface is terminated by one monolayer of indium atoms. (b) (0001), surface is terminated with two layers of metal atoms, with the top layer being entirely In, and second layer containing a mixture of In and Ga.
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EXPERIMENT The studies described here were performed in a combined molecular beam epitaxy (MBE)/surface analysis system, as previously described [2,4]. GaN(0001) was grown on Si-face 6HSiC(0001) substrates, with the polish damage removed by H-etch
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