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

Abstract

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-(AlxGa1−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.