Opto-electrical Properties Of Ga₂O₃-In₂O₃Transparent Conductive Oxide

With the continuous development of transparent optoelectronic devices, the optical andelectrical properties of transparent conductive oxide semiconductors in the deep ultraviolet(UV) region have drawn much attention.Ga2(1-x) In2x O3(Ga2O3-In2O3) solid solution is thecompound alloying with gallium oxide (Ga2O3) and indium oxide (In2O3) in an appropriatecomposition. The optical band gap ofGa2(1-x) In2x O3decreases from4.9eV to3.7eV withincreasing the indium content.Ga2(1-x) In2x O3with a large band gap has such a hightransmittance in the deep-UV region that it can be applied to the deep-UV optoelectronicdevices. However, the electrical conductivity ofGa2(1-x) In2x O3with the perfect stoichiometryis poor. In this paper, the impurity or defect is introduced intoGa2(1-x) In2x O3to improve itselectrical conductivity. This paper can provide some theoretical and experimental guidancesfor the further preparations ofGa2(1-x) In2x O3with a high transmittance in the deep-UV regionand a high conductivity in experiment.Theoretically, the effects of different Sn substitutional sites, different Sn dopingconcentrations and oxygen vacancy on the electronic structures, optical and electricalproperties ofGa2(1-x) In2x O3are studied by the first-principle calculation. Results indicate thatSn–O bonds in Sn-doped Ga1.375In0.625O3have sronger ionic bonds, and Sn4+is preferentiallysubstituted for In3+. Sn-doped Ga1.375In0.625O3is a typical n-type degenerate semiconductor.The impurity bands are mainly provided by the Sn5s states. Ga1.25In0.625Sn0.125O3has asmaller electron effective mass and a slightly larger mobility. However, Ga1.375In0.5Sn0.125O3has a larger relative electron number and a slightly higher conductivity. With increasing theSn doping concentration, the lattice parameters of Sn-doped Ga1.375In0.625O3increase, the bandgap decreases, the relative electron number increases slightly, the electron mobility declines,and the conductivity is enhanced slightly. The Ga1.5In0.5O3with oxygen vacancy VO(3)has themost stable crystal structure. After the introduction of oxygen vacancy, one donor impuritylevel forms around the Fermi level. The ionization energy of electrons in the impurity level ofVO(3)is the largest, so the electrical conductivity is relatively poor. The impurity levels ofGa1.5In0.5O3with VO(1)and VO(2)are mainly provided by Ga4s,4p and O2p states. However,the impurity level of Ga1.5In0.5O3with VO(3)is mainly provided by Ga4s,4p states, In5s,5pstates and O2p states. Ga1.5In0.5O3still has a higher transmittance after the introduction of oxygen vacancy.In experiment, Ga2O3-In2O3:Sn alternating multilayer films are fabricated by radiofrequency (RF) and direct current (DC) magnetron sputtering techniques. The structural,optical and electrical properties of Ga2O3-In2O3:Sn multilayer films change with the numberof repetition periods. The two-period alternating multilayer film with a thickness of72nm hasbetter optoelectronic properties: a low sheet resistance of225.5/sq and a high transmittanceof over62.9%at300nm wavelength. After the annealing treatment, the effect of annealingtemperature on optical and electrical properties of the Ga2O3-In2O3:Sn films is alsoinvestigated. The temperature at whichGa2(1-x) In2x O3solid solution is formed has beenobtained. The two-period alternating multilayer film with the annealing temperature of600Calso has better optoelectrical performances.