p-type layer formation study for Ga2O3 by employing Ni ion implantation with two-step oxygen plasma and thermal annealing

We demonstrated stable local or planar p-type layer formation for Ga2O3. Our concept is to use NiO as the dopant. The process comprises as follows: 58Ni ion implantation into Ga2O3 substrates, followed by activation and crystallinity improvement of implanted 58Ni, and formation of NiO doped layers by applying low-temperature O-radical-based plasma annealing (O-PA) and O2 rapid thermal annealing (O2-RTA). Basic experiments were conducted to clarify the validity of this concept. Results showed that O-PA was more effective than O2-RTA in repairing damage induced by 58Ni implantation. Typical layer evaluation results, including forward and reverse directional electrical characteristics of Ga2O3 diode structures [“NiO doped:” Ni/Ga2O3:NiO(p)/Ga2O3:Sn (n)/Ti, and “Ni/Schottky:” Ni/Ga2O3:Sn (n)/Ti] fabricated using Ga2O3 substrates, are shown. The NiO doped diodes were fabricated using the highest Ni implantation concentration of 1020 cm−3, followed by O-PA and O2-RTA. The NiO doped diodes annealed using two-step annealing, low-temperature O-PA (300 °C, 1 h) and O2-RTA (950 °C, 1 h), showed distinct bipolar rectification characteristics with a forward conduction capability more than twice that of the Ni/Schottky diode. The NiO doped diode surface was evaluated by electron diffraction (ED) analysis. The diffraction pattern for the NiO doped area was that of Ga2O3 but differed somewhat from the pattern for the Ga2O3 substrate. The NiO doping process is considered to generate acceptors in the doped area. We expect our proposed concept to lead to bipolar Ga2O3 devices and other bipolar compound semiconductors with practical acceptor layers.