Layer by Layer Growth of GaN Films by Low Temperature Cyclic Process
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Layer by Layer Growth of GaN Films by Low Temperature Cyclic Process
P. Sanguino1 , S. Koynov1, M. Niehus11, L. V. Melo1, R. Schwarz1 H. Alves2, B. K. Meyer2 1 2
Departamento de Física, Instituto Superior Técnico, Lisboa, Portugal Justus-Liebig-University, Giessen, Germany
ABSTRACT Recently we have proposed a new layer-by-layer method for deposition of group-III nitrides from elemental precursors (Ga, N2). This technique is based on a two-step cyclic process, which alternates Pulsed Laser Deposition (PLD) and nitrogen plasma treatment. We have shown that such a process allows to control independently the structure and the N-content of the growing film. The objective of this work is to develop the cyclic process for achieving high quality GaN films. We explore the opportunities to grow stoichiometric epitaxial films on different substrates at relatively low temperatures (400º C to 600º C). This will gives us the possibility to use ZnO epitaxial layers as a buffer without thermal degradation. UV- Visible transmission spectra, X-ray diffraction scans and Atomic Force Microscopy are some of the tools used to characterise and compare the deposited films.
INTRODUCTION For the last few years, Pulsed Laser Deposition (PLD) has been emerging as a promising alternative technique to MO-CVD and MBE for the deposition of semiconductors of group-III nitrides (GaN, AlN, InN and their alloys) [1-9]. Some of the main inherent advantages are the simplicity and flexibility of the deposition system, the possibility to obtain ultra-clean films and single crystal growth at lower deposition temperatures. The opportunity for a fast switching between depositions of different III-nitride alloys by simply redirecting the laser beam to different multi-component targets is also a very interesting feature. Although the basic principle of the PLD technique is used by all the research groups, most of them incorporate slight variations in order to overcome the inherent problems. Some use ammonia (NH3) as background gas in order to increase the nitrogen incorporation [1-3]. Others were successful in obtaining epitaxial growth of GaN with an atmosphere of molecular nitrogen [4,5] and a few use activated nitrogen generated by a plasma source [6,7]. One of the advantages of using a pure nitrogen source whether or not being molecular, atomic or ionic is that, it is both a safer gas to work with and less aggressive to the deposition chamber. In addition, since it is an extremely pure nitrogen source it does not introduce impurities such as the hydrogen from the NH3 source. Targets used for PLD of GaN also vary from pure liquid Ga [2-5,7], solid Ga [6] and pure GaN sintered powder [1]. It was reported that using liquid gallium target could overcome the problem of target deterioration and large particle droplets over the growing film [2,3,5,8,9]. I3.14.1
In this article we report preliminary results of GaN grown on pre-nitridated sapphire substrates and quartz substrates at temperatures between 400ºC to 600ºC by applying a two step cyclic PLD process
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