Ultralow-Supersaturation Al Pretreatment toward Low Dislocation Density and Low Radio Frequency Loss GaN/AlN Epi-Stacks on High-Resistivity Si Substrates

An ultralow-supersaturation Al pretreatment approach has been proposed to achieve low threading dislocation (TD) density and low radio frequency (RF) loss GaN/AlN layer stacks on Si substrates. By employing this approach, the Al-Si liquid alloy is eliminated, and a sharp AlN/Si interface is obtained. In addition, the size of the AlN nucleation islands is enlarged and thus the TDs generated from the coalescence of the islands are reduced even at a low growth temperature. Owing to the low TD density AlN layer, a 1.5 mu m crack-free GaN layer can be achieved directly on this AlN layer and no transition layers are required. The full width at half maximum values are as low as 390 and 440 arcsec for the GaN (002) and (102) diffractions, respectively. Owing to a low growth temperature and short growth time, the RF loss of the epi-stack is as low as 0.29 dB/mm at 10 GHz. This work shows great potential for the fabrication of high-quality and low-loss GaN-on-Si RF devices.