Low RF loss and low dislocation density of GaN grown on high-resistivity Si substrates

The conductive channel induced by aluminum (Al) diffusion into high-resistivity Si substrates is one of the main contributors to RF loss of GaN-on-Si RF devices. However, it has been unclear how and when the Al diffuses into the substrates. Here, we study the origins of the Al impurity in the substrates. It's revealed that trimethylaluminum (TMAl) flow rate during the pretreatment is a considerable contributor to the Al diffusion. By restricting the TMAl preflow rate, high-quality GaN layers with RF loss of 0.3 dB mm(-1) at 10 GHz and dislocation density of 1.6 x 10(9) cm(-2) have been achieved on Si substrates.