Efficient Acceptor Doping of Sputter-Deposited p-Type Ni _x Ga_1-x O Rocksalt Alloy with Li

Ga2O3 as an ultrawide band gapsemiconductorhas attracted much attention in high-power electronic applications,but its full potential and functionalities have been hampered by itsinability to obtain reliable p-type materials. Previously,we demonstrated p-type Ga2O3 by alloying with NiO in an O-rich environment (Ni x Ga1-x O1+& delta;). This is attributed to the >1.8 eV upward movement of the valenceband maximum (VBM) when the alloy forms a rocksalt structure for x & GSIM; 0.2, making the Ni vacancy (V (Ni)) acceptors to become shallow. Here, we improve the p-type conductivity of Ni x Ga1-x O1+& delta; by extrinsic p-type doping with Li by magnetron sputtering. While stoichiometricNi( x )Ga(1-x )O alloys are highly resistive throughout the whole composition range,Li-doped Ni x Ga1-x O exhibits p-type conductivity with x > 0.4, confirming that despite the lack of a high V (Ni) concentration, Li is an effective acceptorin RS-Ni x Ga1-x O. The doping efficiency of Li is further improved in O-richalloys Ni x Ga1-x O1+& delta; due to the enhanced incorporation ofLi, so that p-type conducting Ni x Ga1-x O1+& delta;:Li alloys with Ni composition as low as x & SIM;0.2 is achieved. With Li doping, the & rho; of Ni-rich alloys with x > 0.5 is <10 & omega;& BULL;cm, which is over an orderof magnitude lower than that in undoped alloys. The enhanced p-type conductivity of Ni x Ga1-x O1+& delta;:Li is in goodagreement with the position of their Fermi level with respect to theVBM, as revealed by VB spectra from X-ray photoelectron spectroscopymeasurements. With further optimization of the doping concentration,these p-type Ni x Ga1-x O1+& delta;:Li films canbe exploited to form p-n junction structures on n-type Ga2O3.