The Chemistry of GaN Growth
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The Chemistry of GaN Growth
T.F. Kuech, Shulin Gu, Ramchandra Wate, Ling Zhang, Jingxi Sun, J.A. Dumesic, and J.M. Redwing 1 University of Wisconsin-Madison, Department of Chemical Engineering, Madison, WI, 53706, 1 Pennsylvania State University, Dept. of Materials Science, University Park, PA, 16802.
ABSTRACT x
The development of new chemically based growth techniques has opened the range of possible GaN applications. This paper reviews some of the challenges in the chemically based growth of GaN and related materials. Ammonothermal-based growth, hydride vapor phase epitaxy and metal organic vapor phase epitaxy (MOVPE) are chemically complex systems wherein the underlying mechanisms of growth are not well understood at present. All these systems require substantial experimental and theoretical efforts to determine the nature and kinetics of GaN growth. In the case of metal organic vapor phase epitaxy, the application of computational techniques based on density functional theory have augmented the more conventional experimental approaches to determining the growth chemistry. These chemical reaction schemes, when combined with computational thermal- fluid models of the reactor environment, provide the opportunity to predict growth rates, uniformity and eve ntually materials properties. GaN Growth Techniques The growth of GaN can be achieved by a variety of chemical approaches. Many of these approaches have met with great success when applied to other materials. Solution-based growth from supercritical fluids, as in the hydrothermal growth of SiO 2 , was developed in the 1960s and 70s into an efficient low-cost means of generating large quantities of bulk crystals under affordable conditions [1]. Hydride vapor phase epitaxy (HVPE) is used as an efficient means to deposit high purity III-V semiconductors at high rates. It has been used in the formation of detector structures based on the InP and GaAs materials systems. Finally, metal organic vapor phase epitaxy (MOVPE) is a premier method for the fabrication of lasers, light emitting diodes, transistors and a host of other device structures in most III-V and II-VI alloy systems. The growth of GaN by any of these established techniques has been difficult due to the chemical complexity or the difficulty in the thermochemical stability of the nitride materials themselves. It is well understood that GaN growth under all conditions is complicated by the high nitrogen activity required for the thermal stability of GaN [2] as well as the broad miscibility gap present at modest temperature in the InGaN alloy system [3]. All of these chemical techniques are currently being used or are under consideration for the growth of ‘bulk’ and epitaxial films of GaN and related alloy materials. Each technique provides a separate cha llenge to the formation of low defect density, chemically pure materials. The extension of the hydrothermal growth technique to GaN presently requires the use of supercritical ammonia. The feasibility of producing nitrides, at least in polycrystalline or p
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