Crystal Growth of β-Ga₂O₃ for Application in Power Electronic Devices

β-Ga₂O₃ is an attractive material for next-generation power devices. β-Ga₂O₃ has a huge bandgap of 4.5-4.9 eV. The critical electric field strength is expected to be 6-8 MV/cm [1]. Its carrier concentration can be controlled in the range of 10¹⁵-10¹⁹ /cm³ by Si or Sn doping [2, 3]. Another important feature of β-Ga₂O₃ is that bulk crystals can be grown by using the melt growth method at low cost.<br/>The techniques for growing large β-Ga₂O₃ bulk crystals include standard methods such as Czochralski, floating zone, edge-defined film-fed growth (EFG), vertical Bridgman (VB) method, etc. The development of the EFG method is the most advanced, and 100-mm wafers are commercially available. The dislocation density of 100-mm wafers is low enough, about 10³-10⁴ /cm². 150-mm wafers were demonstrated a few years ago [4]. The development of the VB method has progressed rapidly in the last few years [5]. 2-3-inch wafers have already been demonstrated. The crystal quality of β-Ga₂O₃ bulk crystals fabricated using the VB method has been shown to be better than those fabricated by the EFG method.<br/>High-voltage β-Ga₂O₃ power devices require high-quality and thick epitaxial films with a low donor concentration. The development of epitaxial growth techniques is underway using molecular beam epitaxy, halide vapor phase epitaxy (HVPE), metal organic chemical vapor deposition (CVD), mist CVD, etc. HVPE is the most suitable method for power-device applications because a high-purity and thick layer can be grown [6]. 100-mm β-Ga₂O₃ epi wafers are commercially available.<br/>We have fabricated β-Ga₂O₃ Schottky barrier diodes (SBDs) to evaluate the crystal quality of 100-mm β-Ga₂O₃ epi wafers. The epi thickness and donor concentration are about 10 μm and 2 x 10¹⁶ /cm³, respectively. 86 devices with 1.6 mm square anode are fabricated on 100-mm epi wafer. All devices show clear forward characteristics with a threshold voltage of about 0.8-0.9 V and small on-resistance. 72% of the devices (62/86 devices) show good reverse characteristics in agreement with the theoretical prediction of thermionic field emission model. From the yield and anode diameter, the killer defect density is estimated to be enough low value of 13 /cm².<br/>Recent progress in β-Ga₂O₃ crystal growth or power devices was explained. Improvements to the crystal quality of 100-150 mm β-Ga₂O₃ wafers are underway. The development of β-Ga₂O₃ SBDs and FETs is accelerating. We hope to further development toward early commercialization of β-Ga₂O₃ power devices.<br/><br/>Part of this work was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan.<br/><br/>[1] M. Higashiwaki et al., Appl. Phys. Lett. <b>100</b> (2012) 013504.<br/>[2] N. Ueda et al., Appl. Phys. Lett. <b>70 </b>(1997) 3561.<br/>[3] E. G. Víllora et al., Appl. Phys. Lett. <b>92</b> (2008) 202120.<br/>[4] A. Kuramata et al., Jpn. J. Appl. Phys. <b>55</b> (2016) 1202A2.<br/>[5] K. Hoshikawa et al., J. Cryst. Growth, <b>546 </b>(2020) 125778.<br/>[6] H. Murakami et al., Appl. Phys. Express, <b>8 </b>(2015) 015503.<br/>[7] K. Sasaki et al., Appl. Phys. Express, <b>10 </b>(2017) 124201.