Ga₂O₃ and AlN—Ultra-Wide Bandgap Semiconductors for Power and RF Electronics

It’s of little surprise that there has been a consistent drive toward the use of wider bandgap materials for power and RF electronics. After all, the wider the bandgap, the greater the breakdown field, opening the door to making devices with a higher breakdown voltage for the same material thickness. Furthermore, the saturation velocity of mobile carriers in ultra-scaled devices tends to be about 1-2 x 10⁷ cm/s in most semiconductors.<br/>However, nature is not always that generous. Typically, a move to a wider bandgap is accompanied by more challenging doping, point defect control, ohmic contacts, quality junctions, along with difficulty in making high-quality native substrates. Ga₂O₃ and AlN are among the promising contenders, given their large bandgaps, availability of large-size bulk substrates (&gt;2 inches), and heterojunctions. But both lack p-type. AlN possesses high thermal conductivity – slightly worse than that of copper but Ga₂O₃ has a low thermal conductivity – worse than that of sapphire.<br/>Given all these promises and obstacles, is it possible to harvest all the benefits in AlN and Ga₂O₃ and demonstrate devices that are superior to those made from SiC and GaN? I will reflect on our efforts in seeking answers to these questions in the past many years researching on power and RF devices with a focus on Ga₂O₃ and AlN [1-7].<br/>References:<br/>[1] Z. Hu <i>et al</i>., Appl. Phys. Lett. 92 85111 (2015) Near unity ideality factor and Shockley-Read-Hall lifetime in GaN-on-GaN p-n diodes with avalanche breakdown.<br/>[2] W. Li <i>et al.,</i> IEEE Trans. Electron Dev. (2020) Guiding principles for trench Schottky barrier diodes based on ultrawide bandgap semiconductors: a case study in Ga₂O₃<br/>[3] A. Hickman et al, SST (2021) Next generation electronics on the ultrawide-bandgap aluminum nitride platform.<br/>[4] A. Green et al, APL Materials (2022) Beta-gallium oxide power electronics.<br/>[5] E.K. Kim et al, APL (2023) N-polar GaN/AlGaN/AlN HEMTs on single-crystal bulk AlN substrates.<br/>[6] W. Zhao et al., IEEE EDL (2023) 15-GHz epitaxial AlN FBARs on SiC substrates.<br/>[7] B. Cromer et al., JVST (2024) Over 6 MV/cm operation in β-Ga2O3 Schottky barrier diodes with IrO2 and RuO2 anodes deposited by molecular beam epitaxy