Perspective—Opportunities and Future Directions for Ga₂O₃

Abstract

The β-polytype of Ga2O3 has a bandgap of ∼4.8 eV, can be grown in bulk form from melt sources, has a high breakdown field of ∼8 MV.cm−1 and is promising for power electronics and solar blind UV detectors, as well as extreme environment electronics (high temperature, high radiation, and high voltage (low power) switching. High quality bulk Ga2O3 is now commercially available from several sources and n-type epi structures are also coming onto the market. There are also significant efforts worldwide to grow more complex epi structures, including β-(AlxGa1x)2O3/Ga2O3 and β-(InxGa1−x)2O3/Ga2O3 heterostructures, and thus this materials system is poised to make rapid advances in devices. To fully exploit these advantages, advances in bulk and epitaxial crystal growth, device design and processing are needed. This article provides some perspectives on these needs.

Ohmic contacts on n-type β-Ga2O3 using AZO/Ti/Au

“…There is significant promise in β-Ga 2 O 3 for use in electronics for extreme environments (high temperature, high radiation and high voltage switching) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] and for solar blind UV detection. 16 Ga 2 O 3 is suited to these applications because of its wide bandgap, ∼4.8 eV and high theoretical critical field strength ∼8 MV/cm (experimental values have reached 3.8 MV/cm).…”

“…13 Ga 2 O 3 bulk and epitaxial crystals can be grown by many methods including Czochralski, edge-defined film-fed growth (EFG), Verneuil, float-zone, molecular beam epitaxy (MBE), halide vapor phase epitaxy growth (HVPE), with excellent control of quality and n-type conductivity. 1,2,14,15,17 The β-phase of Ga 2 O 3 has a monoclinic structure and is the most commonly studied of the different polymorphs. 1,2,[18][19][20][21] Excellent results for β-Ga 2 O 3 -based power rectifiers, field effect transistors (FETs) and metal-oxide FETs (MOSFETs) have been reported, 2,4-13 along with solar blind photodetectors.…”

“…1,2,14,15,17 The β-phase of Ga 2 O 3 has a monoclinic structure and is the most commonly studied of the different polymorphs. 1,2,[18][19][20][21] Excellent results for β-Ga 2 O 3 -based power rectifiers, field effect transistors (FETs) and metal-oxide FETs (MOSFETs) have been reported, 2,4-13 along with solar blind photodetectors. 1,2,16 In all cases, these devices would benefit from an improved low resistance Ohmic contacting process that requires only moderate annealing temperatures.…”

“…1,2,[18][19][20][21] Excellent results for β-Ga 2 O 3 -based power rectifiers, field effect transistors (FETs) and metal-oxide FETs (MOSFETs) have been reported, 2,4-13 along with solar blind photodetectors. 1,2,16 In all cases, these devices would benefit from an improved low resistance Ohmic contacting process that requires only moderate annealing temperatures. 4,8 To date, the lowest specific contact resistance of ∼4.6×10 -6 Ω-cm 2 was reported for Ti/Au contacts on n-Ga 2 O 3 epitaxial layers with Si implanted and annealed at 925 • C followed by dry etching, metal deposition and annealing at 470 • C. 21 Yao et al explored nine different metals with Au capping layers to form Ohmic contact on Ga 2 O 3 , with many current-voltage ( I-V) results being pseudo-Ohmic, and the best results obtained using Ti/Au.…”

Recent Advances in β-Ga2O3–Metal Contacts

“…The suitability of semiconductors for power device applications is usually evaluated by Baliga’s figure of merit (BFOM) [11]. The BFOM of β-Ga 2 O 3 is almost triple that of SiC and GaN, reducing the conduction loss significantly [3, 12–14]. Moreover, the saturation electron velocity is theoretically estimated to be around 2 × 10 7  cm/s, making it alluring for high-frequency operations [15–20].…”