Study of GaN films grown by metalorganic chemical vapour deposition
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Internet Journal o f
Nitride S emiconductor Research
Volume 1, Article 3
Study of GaN films grown by metalorganic chemical vapour deposition W. Van der Stricht, I. Moerman, P. Demeester University of Ghent-IMEC, Department of Information Technology J. A. Crawley, E. J. Thrush Thomas Swan & Co., Ltd. This article was received on May 31, 1996 and accepted on August 5, 1996.
Abstract In this paper GaN films are examined, which are grown on basal plane (0001) sapphire substrates. Growth is performed in a novel type of vertical rotating disk reactor. The effects of several growth parameters on the film quality are discussed. The results on n-type doping of GaN with SiH 4 are presented. The GaN layers were evaluated by surface morphology studies, DC X-ray diffraction, electrical and optical characterisation.
1. Introduction With a wide direct band gap of 3.39 eV and excellent physical properties gallium nitride (GaN) is a very promising material for fabricating blue light emitting devices. A few possible applications are high density optical data storage, full colour video-screens and even traffic lights. Significant progress in epitaxial growth of GaN has already led to commercially available nitride-based high brightness light emitting diodes [1] [2] and very recently the first GaN blue laser was announced [3]. In spite of this recent success the growth of GaN and its alloys remains a challenge. High quality GaN has been grown by several epitaxial techniques, such as MOCVD and MBE. At the moment MOCVD seems to be the most successful and certainly the most promising for large scale production. Nakamura attributes his success in nitride research to the two flow reactor, which was designed especially for nitride growth [4]. However several reactor designs have been suggested to tackle the specific problems associated with GaN growth. In this paper the achievements in GaN deposition in a novel type of vertical rotating disk MOCVD reactor are demonstrated. The optimisation of growth parameters and the characterisation of GaN films is discussed.
2. Experiment 2.1. The MOCVD-reactor GaN films were grown by metalorganic chemical vapour deposition on two inch sapphire (0001) substrates with a H2 and mixed H2/N2 carrier gas. Ammonia (NH3) and trimethylgallium (TMG) were used as source materials. The growth was conducted in a vertical rotating disk reactor, manufactured by Thomas Swan & Co (see Figure 1). The group III and group V elements are injected separately into the reactor through a water cooled "showerhead" to avoid undesired upstream pre-reactions. Because the “showerhead» consists of several hundred fine tubes, the gasses are introduced uniformly into the reactor. A graphite resistance heater is used to raise the temperature of a graphite susceptor up to 1200 °C. The temperature is measured with an optical pyrometer looking directly at the substrate or the susceptor (three positions are available to monitor the temperature profile during growth). The substrate is placed on a rotating susceptor to achieve an improv
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