Activation of implanted Si, Ge, and Sn donors in high-resistivity halide vapor phase epitaxial β-Ga2O3:N with high mobility
Joseph Spencer, Marko J. Tadjer, Alan G. Jacobs, Michael A. Mastro, John L. Lyons, Jaime A. Freitas, James C. Gallagher, Quang Tu Thieu, Kohei Sasaki, Akito Kuramata, Yuhao Zhang, Travis J. Anderson, Karl D. Hobart
Abstract
Activation of implanted donors into a highly-resistive, nitrogen-doped homoepitaxial β-Ga2O3 has been investigated. Nitrogen acceptors with the concentration of ∼1017 cm−3 were incorporated during epitaxial growth yielding low-doped (net donor concentration <1014 cm−3) films subsequently implanted with Si, Ge, and Sn. Upon Ohmic contact formation to the implanted regions, sheet resistance values of 314, 926, and 1676 Ω/sq were measured at room temperature for the Si-, Ge-, and Sn-implanted samples, respectively. Room temperature Hall measurements resulted in sheet carrier concentrations and Hall mobilities of 2.13 × 1014 /93, 8.58 × 1013/78, and 5.87 × 1013/63 cm2/(V s), respectively, for these three donor species. Secondary ion mass spectroscopy showed a volumetric dopant concentration of approximately 2 × 1019 cm−3 for the three species, resulting in carrier activation efficiencies of 64.7%, 40.3%, and 28.2% for Si, Ge, and Sn, respectively. Temperature-dependent Hall effect measurements ranging from 15 to 300 K showed a nearly constant carrier concentration in the Si-implanted sample, suggesting the formation of an impurity band indicative of degenerate doping. With a bulk carrier concentration of 1.3 × 1019 cm−3 for the Si implanted sample, a room temperature mobility of 93 cm2/(V s) is among the highest reported in Ga2O3 with a similar carrier concentration. The unimplanted Ga2O3:N regions remained highly resistive after the surrounding areas received implant and activation anneal. These results open the pathway for fabricating Ga2O3 devices through the selective n-type doping in highly resistive epitaxial Ga2O3.