ABSTRACT
Gallium nitride (GaN) is an attractive material for use in optoelectronics, high-power, high-temperature and high-frequency electronic devices. Sapphire substrates have been widely used for the growth of GaN films. It is, however, difficult to grow high-quality GaN films because of lattice and thermal mismatches between GaN and sapphire. For the present, the most popular method of GaN epitaxial growth is to use thin aluminium nitride (AIN) or GaN films deposited at low-temperatures on sapphire substrates as a buffer layer.[1-5] The GaN films grown on sapphire substrates with low temperature buffer layers show high dislocation densities and residual stresses. Other substrate materials and/or various templates have been reported to solve these problems. However, several problems, such as high dislocation densities and residual stresses, are not yet satisfactorily solved. In this study, we show that high-quality epitaxial aluminum nitride (AIN) films grown on sapphire at high temperatures higher than 1000 °C are promising templates for GaN epitaxial growth. We expect high-quality GaN to be grown on these AIN films because the difference between the lattice constants of AIN and GaN is 3 % at most and the thermal expansion coefficient of GaN is close to that of AIN. Previously, GaN films have been reported to be grown on AIN films (grown at high temperature). [6,7] In this paper we have clarified to greatly improve the electrical, crystal, optical quality of GaN films on epitaxial AIN films for the first time.
