P-type conductive Ga₂O₃ epilayers grown on sapphire substrate by phosphorus-ion implantation technology

This study utilized various phosphorus-ion implantation techniques, incorporating low, medium, and high doses, to investigate the electrical properties of unintentionally doped β-Ga2O3 epilayers. These epilayers were grown on sapphire substrates by metalorganic chemical vapor deposition. Specifically, the low-dose implantation involved phosphorus ions at concentrations of 1.6✕10¹³, 1✕10¹² and 2.5✕10¹² atoms/cm², administered at implantation energies of 100, 50, and 40 keV, respectively. The medium-dose implantation utilized phosphorus ions at concentrations of 1.6✕10¹⁴, 1✕10¹³ and 2.5✕10¹³ atoms/cm², at the same implantation energies. Finally, the high-dose implantation employed phosphorus ions at concentrations of 1.6✕10¹⁵, 1✕10¹⁴ and 2.5✕10¹⁴ atoms/cm², with implantation energies of 100, 50, and 40 keV, respectively. The implantation parameters were also simulated using the Stopping and Range of Ions in Matter software, while the actual concentration of phosphorus ions was measured via secondary ion mass spectrometry. Subsequently, Ni and Au were deposited on the annealed phosphorus-implanted β-Ga₂O₃ epilayers, followed by rapid thermal annealing at 600 °C in a nitrogen environment for 1 min, for Hall measurement. The electrical properties of the phosphorus-implanted β-Ga₂O₃ epilayers were assessed through Hall measurements. Notably, the β-Ga₂O₃ epilayers implanted with middle and high doses displayed p-type behavior. The resistivity of the p-type β-Ga₂O₃ epilayers with middle and high doses measured 9.699 and 6.439 Ω cm, respectively, as determined by Hall measurements. Additionally, the hole carrier concentrations for these doses were measured as 1.612 × 10¹⁸ and 6.428 × 10¹⁷, respectively. Consequently, the phosphorus ion implantations using middle and high doses were proven effective in obtaining p-type Ga₂O₃. To further explore the defect formation energies and Fermi energies of substitutional phosphorus defects within the β-Ga₂O₃ lattices, first-principles density-functional simulations were employed.