【Epitaxy Papers】Limitations on activation of high dose Ge implants in β-Ga₂O₃

      Researchers from the Cornell University have published a dissertation titled " Limitations on activation of high dose Ge implants in β-Ga₂O₃" in Journal of Applied Physics.

Abstract

      Among ultrawide bandgap semiconductors, β-Ga₂O₃ is particularly promising for high power and frequency applications. For devices, n-type concentrations above 10¹⁹ cm⁻³ are required. Ge is a promising alternative n-type dopant with an ionic radius similar to Ga. Homoepitaxial (010) β-Ga₂O₃ films were implanted with Ge to form 50 and 100 nm box concentrations of 3 × 10¹⁹ and 5 × 10¹⁹ cm⁻³, with damage ranging from 1.2 to 2.0 displacements per atom. For lower damage implants, optimized anneals in ultrahigh purity N₂ at 950–1000 °C for 5–10 min resulted in an R_s of 600–700 Ω/□, mobilities of 60–70 cm²/V s, and a Ge activation of up to 40%. For higher damage implants, activation dropped to 23% with similar mobilities. Ge diffusion, measured by secondary ion mass spectrometry, showed the formation of a Ge “clustering peak” with a concentration exceeding the initial implant following anneals in N₂ or O₂ at 950–1050 °C. Beyond this peak, minimal Ge diffusion occurred for N₂ anneals at 950 °C, but at 1050 °C, non-Fickian diffusion extended to >200 nm. Electrical activation data suggest that clustered Ge is electrically inactive. To understand Ge clustering, several samples were characterized by synchrotron x-ray diffraction. Second-phase precipitates were observed in as-implanted samples, which then fully dissolved after furnace annealing in N₂ at 1050 °C. Diffraction peaks suggest that these implant-induced precipitates may be related to a high pressure Pa-3 phase of GeO₂ and may evolve during anneals to explain the Ge clustering. Ultimately, we believe that Ge clustering limits the activation of implanted Ge at high concentrations.

DOI：

https://doi.org/10.1063/5.0310900