Indium incorporation and surface segregation during InGaN growth by molecular beam epitaxy: experiment and theory
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Internet Journal Nitride Semiconductor Research
Indium incorporation and surface segregation during InGaN growth by molecular beam epitaxy: experiment and theory Huajie Chen1, R. M. Feenstra1, J. Northrup2, Jörg Neugebauer3 and D. W. Greve4 1Department
of Physics, Carnegie Mellon University, Palo Alto Research Center, 3Fritz-Haber-Institut der MPG, 4Department of Electrical and Computer Engineering, Carnegie Mellon University, 2Xerox
(Received Tuesday, June 5, 2001; accepted Tuesday, June 26, 2001)
InGaN alloys with (0001) or (0001) 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 (0001) polarities. Evidence for the existence and stability of a structure containing two adlayers of indium on the Inrich InGaN(0001) surface is presented. 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.
1 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 (0001) 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 decreaseswhen 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 Figure 1. Figure 1(a) shows the previously determined structure for the InGaN(0001) 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 gallium. For the InGaN(0001) surface, prior studies indicate that the surface most commonly 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 gallium atoms [3] [4]. This structure is illustrated in Figure 1(b). 2
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 6H-SiC(0001) substrates, with the polish damage removed by H-etching [5]. After the Hetching, the substrate was introduced into the growth chamber and outgassed up to the temperature of 800°C. A few monolayers of Si were deposited on
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