GaN-on-Porous Silicon for RF Applications

Gallium nitride (GaN) is a promising semiconductor for RF and high-power applications. However, its large-scale industrialization is hindered by several challenges, primarily the lack of cost-effective, high-performance handle substrates. Sapphire and SiC present high performances, but their use in electronic applications is limited due to their high cost. GaN-on-Si substrates are more affordable but suffer from high substrate-induced RF losses. We introduce an innovative method to mitigate the substrate losses. Porous silicon is known for decades for its high RF performance, but its integration is challenging. We performed porosification of the handle silicon substrate after the fabrication of the RF devices, from the backside, preserving the high quality of the GaN layers and the low cost of GaN-on-Si, while boosting the RF performances. We achieved harmonics H2 =-140 dBm at Pout=15 dBm, RF losses under 0.1 dB/mm at 5 GHz, and an effective resistivity higher than 8 kΩ·cm at 5 GHz.