Controlling the electrical conductivity of ternary wurtzite-type and metastable β -AgGaO₂ by impurity doping

We studied electron carrier doping into the ternary wurtzite β-AgGaO₂ by impurity doping. Ti-doped β-NaGaO₂, i.e., β-Na(Ga_1-xTi_x)O₂, was prepared by a conventional high-temperature solid-state reaction; then, we performed ion-exchange of Na⁺ ions with Ag⁺ ions into the Ti-doped β-NaGaO₂ in a molten nitrate salt to produce Ti-doped β-AgGaO₂: β-Ag(Ga_1-xTi_x)O₂. A single ternary wurtzite phase was obtained at compositions of 0≤x≤0.05. Ti-doped β-AgGaO₂ showed an electrical conductivity at room temperature that was one to three orders of magnitude higher than that of undoped β-AgGaO₂. The Ti-doped β-AgGaO₂ samples showed an electron carrier density in the range of 10¹⁸-10¹⁹ cm^-3, based on the free-carrier absorption shown in their optical absorption spectra. These results show that carrier injection by impurity doping into metastable β-CuM^IIIO₂ and β-AgM^IIIO₂ is possible by using an impurity-doped β-NaGaO₂ precursor. This result encourages the development of optoelectronic devices based on the narrow-band-gap oxide semiconductors of β-CuM^IIIO₂ and β-AgM^IIIO₂.