Properties of Digital Aluminum Gallium Nitride Alloys Grown via Metal Organic Vapor Phase Epitaxy
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Properties of Digital Aluminum Gallium Nitride Alloys Grown via Metal Organic Vapor Phase Epitaxy L. E. Rodak1 and D. Korakakis1,2 1 Lane Department of Computer Science and Electrical Engineering, West Virginia University, PO Box 6109, Morgantown, WV 26506, USA 2 National Energy Technology Laboratory, National Energy Technology Laboratory, 3610 Collins Ferry Road, Morgantown, WV 26507, USA ABSTRACT Deep Ultra Violet (UV) emitters are of particular interest for applications including, but not limited to, biological detection and sterilization. Within the III-Nitride material system, Aluminum Gallium Nitride (AlxGa1-xN) alloys are the most promising for UV device fabrication due to the wide, direct band gap. The growth of high quality AlxGa1-xN alloys via Metal Organic Vapor Phase Epitaxy (MOVPE) is challenging due to large sticking coefficient of the Al species compared to that of Ga and also the high reactivity of Al precursors. As a result, films are often characterized by large dislocation densities, cracks, and poor conductivity. Digital alloy growth, or Short Period Superlattices (SPS), consisting of layers of binary or ternary alloys with a period thickness of a few monolayers has been shown to be a viable means of growing high quality ternary alloys via Metal Organic Vapor Phase Epitaxy (MOVPE). In certain materials, such as AlGaInP, the electronic properties of digitally grown alloys differ considerably from the equivalent random alloy. Specifically, the bandgap has been shown to differ significantly from the equivalent random alloy. As a result, digital alloy growth presents the potential to further engineer material properties. However, the influence of digital growth on the electronic properties of III-Nitride alloys has not been extensively characterized. This study focuses on Aluminum Gallium Nitride (AlxGa1-xN) alloys grown using a digital technique via MOVPE. The influence of the growth technique over a wide range of compositions is reported along with the electronic properties. INTRODUCTION Aluminum Gallium Nitride (AlxGa1-xN) alloys are of particular interest for Ultra Violet (UV) applications due to the wide direct bandgap characteristic of III-Nitride alloys. The bandgap can range from 3.4 eV to 6.2 eV as the Al concentration is varied from x = 0 to x = 1 and as a result the emission spans through the near UV and into the deep UV regime. When grown via Metal Organic Vapor Phase Epitaxy (MOVPE), Al containing alloys are inherently difficult to grow due to the short diffusion length of the Al species and also the high reactivity of the Al containing precursors[1]. This requires high growth temperatures and low reactor pressures when compared GaN growth conditions. As such there has been considerable interest in the development of alternative growth techniques which yield high quality AlxGa1-xN films. Modulated Precursor Expitaxial Growth (MPEG) for example has been one technique reported to yield high quality films in which the metal-organic and ammonia precursor are introduced into the
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