Study Of Epitaxial Lateral Overgrowth Of Gallium Nitride On Sapphire By MOCVD

In this paper, the sapphire wafer was etched previously; then GaN was deposited on patterned sapphire wafers as the ELO technique without mask by Metal Organic Chemical Vapor Deposition (MOCVD). The properties of GaN layer grew by this method was compared with the GaN layer under the same growth process but without etched substrate, and they were investigated by double crystal X-ray diffraction, atomic force microscopy, wet chemical etching and scanning electronic microscopy. The results proved that thinner full-width at half- maximum (FWHM), higher intensity value of X-ray diffraction,smoother surface and lower density value of the etching pit were received using patterned substrate, which made sure that under the same growth process the density of the dislocations decreased 50%. The crystal structure and the growth mechanism were analyzed. Because the positions of pits are the concentration of dislocations, this growing mechanism inhibits the dislocations to extend. While the place where has no pit, the dislocations would bend for 90°as the epilayer growing. So the density of the dislocations was decreased by this method. In addition, because there were also hollows between the pits and the epilayer, which could release the stress of the material and improve the quality of the epilayer.Basing on this epitaxial lateral overgrowth without mask technics, the effects of different growth conditions on the GaN epilayer were also studied. Then the effects of the growth pressure of buffer layer on the growth velocity were investigated with the aid of laser-bounce in situ monitoring tool. The results showed that higher pressure would induce higher growth velocity, but little effect on High-Temperature epilayer. The effects of the thickness of buffer layer,the multi-buffer-layer structure (Low Temperature insert layer and Intermediate-Temperature insert layer) and different values ofⅤ/Ⅲon the High-Temperature GaN epilayer were also studied. The results showed that multi-buffer-layer structure could decrease the density of the dislocations and improve the quality of the crystal structure. The GaN epilayer with Intermediate-Temperature insert layer had the best results of all the samples.