Efficient Acceptor Doping of Sputter-Deposited p-Type Ni_xGa_1-xO Rocksalt Alloy with Li

Ga₂O₃ as an ultrawide band gap semiconductor has attracted much attention in high-power electronic applications, but its full potential and functionalities have been hampered by its inability to obtain reliable p-type materials. Previously, we demonstrated p-type Ga₂O₃ by alloying with NiO in an O-rich environment (Ni_xGa_1-xO_1+δ). This is attributed to the >1.8 eV upward movement of the valence band maximum (VBM) when the alloy forms a rocksalt structure for x ≳ 0.2, making the Ni vacancy (V_Ni) acceptors to become shallow. Here, we improve the p-type conductivity of Ni_xGa_1-xO_1+δ by extrinsic p-type doping with Li by magnetron sputtering. While stoichiometric Ni_xGa_1-xO alloys are highly resistive throughout the whole composition range, Li-doped Ni_xGa_1-xO exhibits p-type conductivity with x > 0.4, confirming that despite the lack of a high V_Ni concentration, Li is an effective acceptor in RS-Ni_xGa_1-xO. The doping efficiency of Li is further improved in O-rich alloys Ni_xGa_1-xO_1+δ due to the enhanced incorporation of Li, so that p-type conducting Ni_xGa_1-xO_1+δ:Li alloys with Ni composition as low as x ∼ 0.2 is achieved. With Li doping, the ρ of Ni-rich alloys with x > 0.5 is <10 Ω·cm, which is over an order of magnitude lower than that in undoped alloys. The enhanced p-type conductivity of Ni_xGa_1-xO_1+δ:Li is in good agreement with the position of their Fermi level with respect to the VBM, as revealed by VB spectra from X-ray photoelectron spectroscopy measurements. With further optimization of the doping concentration, these p-type Ni_xGa_1-xO_1+δ:Li films can be exploited to form p-n junction structures on n-type Ga₂O₃ © 2023 American Chemical Society.