The dawn of Ga₂O₃ HEMTs for high power electronics - A review

Recently, there is a growing interest in Gallium Oxide (Ga₂O₃) as a promising semiconductor material for intended applications in RF, power electronics, and sensors with high capabilities over existing technologies due to its excellent material characteristics like large bandgap, well-controlled doping, and availability of large size inexpensive substrates. Bulk crystals of monoclinic β-Ga₂O₃ can be grown using melt growth techniques, which ensures large, uniform substrates with relatively low-cost per wafer as compared to GaN and SiC substrates which are usually grown using vapor growth techniques. A large critical field of β-Ga₂O₃ is beneficial for improving the DC performance of high voltage rectifiers and metal oxide semiconductor field-effect transistors (MOSFETs) and facilitates further lateral scaling of FETs for improved RF performance. Band structure of β-Ga₂O₃ indicates difficulty in p-type conductivity, so previously reported most of the β-Ga₂O₃ MOSFETs have been depletion mode, although enhancement mode operations were also demonstrated using recess-gate and charge-trapping gate stack structure. The β-Ga₂O₃ heterostructures have been widely reported using a high-quality epitaxial layer of β-(Al_xGa_1−x)₂O₃ after alloying Al with Ga₂O₃. The β-Ga₂O₃ modulation-doped FETs (MODFETs) have shown two-dimensional electron gas (2DEG) density of ~10¹² cm⁻² that form a good quality channel at the interface. Despite low room temperature electron mobility of around 180 cm² V⁻¹s⁻¹, peak mobility of around 2800 cm² V⁻¹s⁻¹ at 50 K was measured in the latest reported experimental work of β-Ga₂O₃ MODFET. III-nitride based GaN high electron mobility transistors (HEMTs) have been widely used in high power electronics and have shown 2DEG density ~ 10¹³ cm⁻² and channel mobility of 2000 cm² V⁻¹s⁻¹. This paper gives a perspective of Ga₂O₃ material towards making high electron mobility transistors (HEMTs) for a certain class of RF applications. Due to low in-plane lattice mismatch, a high-quality epitaxial layer of GaN and AlN have been grown on β-Ga₂O₃. Furthermore, due to the inherent polarization property of III-nitrides and large bandgap, higher 2DEG density ~10¹³ cm⁻² and large conduction band offset >1.5 eV can be expected in AlN/β-Ga₂O₃ heterostructure. The various defects in WBG devices and their effects on the reliability aspects are also addressed.