Influence of the growth temperature of the high-temperature AlN buffer on the properties of GaN grown on Si(1 1 1) substrate

We have studied the influence of the growth temperature of the high-temperature (HT) AlN buffer layer on the properties of the GaN epilayer which was grown on Si(111) substrate by metalorganic chemical vapor deposition (MOCVD). It was found that the crystal quality of the GaN epilayer strongly depends on the growth temperature of the HT-AlN buffer. The growth temperature of the AlN buffer to obtain high-quality GaN epilayers lies in a narrow window of several tens of degrees. When the temperature is lower than a certain temperature range, the appearance of AlN polycrystals results in the deterioration of the crystal quality of the AlN buffer layer, which is greatly disadvantageous to the coalescence of the GaN epilayer. Although the AlN buffer's crystal quality is improved as the growth temperature increases, the Si outdiffusion from the substrate is also enhanced when the temperature is higher than a certain temperature range, which will demolish the subsequent growth of the GaN epilayer. Therefore, there exists an optimum growth temperature range of the AlN buffer around 1080°C for the growth of high-quality GaN epilayers.