The Growth of GaN Using Plasma Assisted Metalorganic Vapour Phase Epitaxy

Abstract

Conventional metalorganic vapour phase epitaxy (MOVPE) has been very successful in providing high quality GaN films, however, the growth takes place at high temperature and thus requires large flow rates of high purity ammonia. In order to avoid such high and costly use of ammonia, we have developed a novel ultra high vacuum plasma assisted process, which enables us to grow GaN films at much lower temperature (600 to 800 °C). Growth takes place at a total pressure of approximately 10–4 mbar using flow rates for nitrogen or ammonia of 10 to 30 sccm and metalorganic flow rate of less than 1 sccm for growth rates of 1 μm/h. For growth with nitrogen, active species are provided using a rf plasma source. We have studied the influence of the group-V to group-III ratio on the structural, electrical and optical properties of the films, by varying the metalorganic flow rate. There is an optimum V:III ratio, which results in films with the best crystal quality and the lowest sheet resistivity, however, the optimum V:III ratio for band emission occurs at a different V:III ratio. The films show yellow luminescence the intensity of which also varies with V:III ratio. We have also studied the influence of group-V flow rate on the relative intensities of ions and neutral species produced by the plasma activation process and their influence on the properties of the films.