Structure and optical properties of MOVPE and HVPE GaN films grown on GaN nanocrystalline powder substrate
A new approach to fabricate GaN films has been proposed. The GaN films were grown by both the metalorganic chemical vapor phase epitaxy (MOVPE) and the hydride vapor phase epitaxy (HVPE) on GaN nanocrystalline powder compressed to a wafer substrate. GaN powder has been synthesized by reacting gallium oxide (Ga2O3) with ammonia (NH3) using a horizontal quartz reactor. The samples were examined by X-ray diffraction (XRD) and photoluminescence (PL). XRD reveals that the GaN powder and MOVPE and HVPE GaN films are of single-phase wurtzite structure. In the case of GaN powder, XRD spectra typical of powder with a lot of diffraction peaks related to different crystallographic directions have been observed. In the case of the MOVPE and HVPE GaN films, the XRD spectrum has changed significantly. It has been observed that some directions of the growth are favorable, e.g. in the case of HVPE film, the peaks related to (0 0 2) and (1 0 3) directions start to be evidently dominating. Also, it has been observed that PL spectrum for the GaN films is completely different from the one for GaN powder. In the case of GaN powder, only a broad yellow emission has been observed, while in the case of MOVPE and HVPE GaN films, very weak yellow emission and strong emission related to the band gap has been found.