One of the challenges for GaN-on-Si radio frequency (RF) device applications is the RF loss, which is mainly associated with a parasitic channel formed at the interface of AlN and high-resistivity Si substrates. However, the type of conductivity and formation mechanism of the parasitic channel remains controversial. Here, we report unambiguous evidence of Al diffusion at the AlN/Si interface and its effect on RF loss. Hall measurements reveal p-type conductivity at the interface. By combining with secondary ion mass spectroscopy measurements, the p-type conductivity is attributed to the Al diffusion from the AlN layers into the Si substrates, with Al being an acceptor in Si. Experimental data and simulations are in good agreement. We also demonstrate that substrate nitridation can indeed promote the formation of an amorphous silicon nitride layer, which plays a role in suppressing the Al diffusion and, thus, reducing the RF loss.

We have investigated the growth of AlN films on hexagonal nano-concave-circle patterned Si substrates using metal–organic chemical vapor deposition. By depositing a thin AlN seed layer on the Si substrate before the pattern process, a high quality AlN film with a thickness of 2 μm has been obtained. The full width at half maximum values of X-ray diffraction rocking curves are as low as 409 and 677 arc sec for AlN (002) and (102) planes, respectively. Further experimental results indicate that the AlN seed layer can suppress the misorientation of the adjacent grains, as revealed by the lower twist and tilt angles of the mosaic structure, and thus only a few dislocations generated during the grain coalescence. In addition, the migration of Al adatoms is enhanced on the Al terminated surface of the AlN seed layer, which accelerates the coalescence process. All these improvements are attributed to the lower binding energy and diffusion barrier for Al adatoms on the Al terminated surface than that on the Si surface. Our results demonstrate an effective approach to obtain high quality AlN films for high performance ultraviolet light-emitting diodes on the Si substrate.

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In this work, we study the impacts of different types of strain relief layer (SRL) on dynamic on-resistance (Ron) degradation of GaN power devices on Si by back-gate ramping and vertical leakage measurement. Our study reveals that the SRL has important effects on the dynamic Ron. Compared with step-graded AlGaN SRL, the superlattice SRL possesses much more energy barriers, which can more effectively block the leakage of holes from GaN buffer and the injection of electrons from Si substrate. Enhancing the carrier blocking ability of SRL could contribute to the suppression of dynamic Ron degradation.

High quality GaN films on SiC with low thermal boundary resistance (TBR) are achieved by employing an ultrathin low Al content AlGaN buffer layer. Compared with the conventional thick AlN buffer layer, the ultrathin buffer layer can not only improve the crystal quality of the subsequent GaN layer but also reduce the TBR at the GaN/SiC interface simultaneously. The ultrathin AlGaN buffer layer is introduced by performing a pretreatment of the SiC substrate with trimethylaluminum followed by the growth of GaN with an enhanced lateral growth rate. The enhanced lateral growth rate contributes to the formation of basal plane stacking faults (BSFs) in the GaN layer, where the BSFs can significantly reduce the threading dislocation density. We reveal underling mechanisms of reducing TBR and dislocation density by the ultrathin buffer layer. We propose this work is of great importance toward the performance improvement and cost reduction of higher power GaN-on-SiC electronics.