MOVPE Growth and Structural Characterization of Al x Ga 1-x N
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Internet Journal o f
Nitride S emiconductor Research
Volume 2, Article 27
MOVPE Growth and Structural Characterization of AlxGa1-xN S. Ruffenach-Clur, Olivier Briot, Bernard Gil, Roger-Louis Aulombard Groupe d'Etude des Semiconducteurs, GES-CNRS J. L. Rouviere CEA/Grenoble, Département de Recherche Fondamentale sur la Matière Condensée/SP2M This article was received on June 9, 1997 and accepted on September 12, 1997.
Abstract The ternary alloy GaAlN has been grown by low pressure MOVPE (76 Torr) using triethylgallium, trimetylaluminum and ammonia as precursors. The alloy layers were grown on (0001) sapphire substrates using a low temperature AlN buffer. All layers were deposited at a growth temperature of 980°C. Only the aluminum/gallium ratio in the gas phase was changed, keeping the total group III molar flow rate and V/III molar ratio constant. The aluminum incorporation versus gas phase composition was determined experimentally, using energy dispersive analysis of X-rays (EDAX), and X-ray diffraction. We propose a model, taking into account kinetically limited mass transport of group III species in the gas phase, which describes well the data. The structural quality of the layers was investigated using X-ray diffraction and TEM experiments. A degradation of the materials quality is observed with increasing Al content. In this case, growth originate on the buffer grains facets resulting in a “ two directional » growth. This phenomenon, being markedly enhanced when increasing the Al content will be detailed in this paper.
1. Introduction The AlGaN alloy is a solid solution over the whole range of composition and has a direct band gap from 3.4 to 6.2 eV. Therefore, it is a promising material for devices application in the visible range when associated to InGaN [1] [2], and in the UV range for photodetectors [3]. To obtain high quality AlGaN for electronic application, it is necessary to study at first the growth mechanisms involved in the AlGaN growth. Therefore, we study the aluminum gallium nitride solid solution in the whole range of composition, varying the gas phase composition for 10% from one sample to another. This leads us to establish a model for the aluminum incorporation into the solid phase. We were very careful to keep all the growth parameters constant, even the total group III molar flow rate. We observed a decrease in the epilayer crystalline quality with increasing Al content as demonstrated by TEM, and X-Ray diffraction. Indeed, at high Al contents (above 50% aluminum), a second crystalline orientation appears resulting in a “ two directional » growth induced by the buffer layer.
2. Experimental The AlGaN epilayers were grown using triethylgallium, trimethylaluminum and ammonia by low pressure (76 Torr) MOVPE. The layers were deposited onto a 500 Å AlN buffer layer grown at low temperature on a c-face sapphire substrate. We grew layers covering the whole range of AlGaN composition from GaN up to AlN. The data concerning the growth are tabulated (Table1). The organometallic bubbler temperat
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