Fabrication and Characterization of High-Voltage NiO/β-Ga2O3 Heterojunction Power Diodes

This work presents the fabrication and characterization of a high-performance vertical Nickel oxide (NiO)/Beta gallium oxide ( β-Ga ₂ O ₃ ) heterojunction p-n diode. The heterojunction was fabricated by sputtering a p-NiO thin film onto an epitaxial n ^- - β-Ga ₂ O ₃ drift layer. The sputtered NiO, revealed to be polycrystalline, showed an improved crystallinity after annealed in an oxygen ambient, while a seamless contact with the underneath single crystalline β-Ga ₂ O ₃ was observed. A high hole concentration of 1- 3×10 ¹⁹ cm ^-3 and an improved Ohmic contact were also obtained by the annealing process, as confirmed by the Hall and TLM measurements, respectively. A high breakdown voltage ( V _B ) of 1.4 kV and a low specific ON-resistance ( R _on,sp ) of 2.7 mΩ·cm ² were simultaneously achieved for the fabricated diodes, yielding a superior Baliga's figure-of-merit (BFoM) of 0.73 GW/cm ² . From the temperature-dependent current-voltage ( I- V) measurements, two carrier transport mechanisms, namely interface recombination and multistep tunneling, have been identified in the forward conduction of the NiO/ β-Ga ₂ O ₃ heterojunction. The fast recovery property of the device, which was revealed by a double-pulse test, further confirmed the purposed carrier transport mechanisms.