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Rather than moving the emission wavelength

through deep impurity levels, the more efficient band edge transition, that necessitates an InxGal.×N (x > 0.2) active layer may be a better alternative to achieve light emitting devices that emit from the blue through orange region of the visible spectrum. While there have been many reports on the growth of high quality GaN films by MOCVD in recent years, fewer reports have been published on the growth of high quality ln,,Gal-xN, having structural and optical properties that are approaching device quality. In addition to the usual problems facing MOCVD III-nitride growth such as the lack of suitable substrates, the growth of InGaN alloys by MOCVD can suffer from several other difficulties. These difficulties include: 1) The high equilibrium vapor pressure of nitrogen that is required during growth to prevent the dissociation of the In-N bond. The equilibrium vapor pressure of nitrogen over InN, for example, is several orders of magnitude greater than that of AIN and GaN. 5 2) In based compounds suffer from parasitic gas phase reactions between organometallic sources and hydride precursors. It seems that these parasitic reactions are more severe when NH3 is used relative to the AsH 36 and the PH 37 cases, especially when In based organometallics (OMs) are used. 3) AIGaN/InGdN heterostructures can suffer from the fairly high lattice mismatch between these ternary alloys. The quaternary alloy AIInGaN can offer a lattice matched platform for InGaN growth, but this quaternary

273 Mat. Res. Soc. Symp. Proc. Vol. 395 0 1996 Materials Research Society

alloy has barely been studied. 4) High quality interfaces between the InGaN wells and the AIGaN or AIInGaN barrier layers can be difficult to achieve. Poor interfaces can result from poor nucleation (3D vs 2D), lattice mismatch, surface reconstruction, segregation and reaction of In at the interfaces and incompatible growth temperatures. In this paper we report on the growth of In,,Gal-xN (0 < x < 0.40) epitaxial films and AIGaN/InGaN double heterostructures (DHs). These MOCVD grown films were deposited on buffer layers grown by Atomic Layer Epitaxy (ALE) in a specially designed hybrid growth system. EXPERIMENT A versatile growth system, capable of operating in several growth modes, has been designed for the growth of Ill-N compounds. The versatility of the system arises

from its unique susceptor design, shown in Figure 1. For this work the system was operated in two growth modes, ALE mode, for the growth of buffer layers, and conventional MOCVD mode, for the growth of the InGaN alloys. Either growth mode could be selected on demand at any time during a growth experiment. For the conventional MOCVD mode (Figure 1), the substrate is kept stationary under a mixed flow of column III and V precursors. NH3 OMs + N2

N2

N2 N2

N2

Rotatin g part

Figure 1. Susceptor design - conventional MOCVD growth mode. To improve the quality of the deposited films, a novel configuration of quartz tubes minimizes parasitic gas phase mixing of the