Chemical spray pyrolysis deposition and characterization of p-type CuCr1−xMgxO2 transparent oxide semiconductor thin films

A chemical spray pyrolysis technique for deposition of p-type Mg-doped CuCrO2 transparent oxide semiconductor thin films using metaloorganic precursors is described. As-deposited films contain mixed spinel CuCr2O4 and delafossite CuCrO2 structural phases. Reduction in spinel CuCr2O4 fraction and formation of highly crystalline films with single phase delafossite CuCrO2 structure is realized by annealing at temperatures ⩾700 °C in argon. A mechanism of synthesis of CuCrO2 films involving precursor decomposition, oxidation and reaction between constituent oxides in the spray deposition process is presented. Post-annealed CuCr0.93Mg0.07O2 thin films show high (⩾80%) visible transmittance and sharp absorption at band gap energy with direct and indirect optical band gaps 3.11 and 2.58 eV, respectively. Lower (∼450 °C) substrate temperature formed films are amorphous and yield lower direct (2.96 eV) and indirect (2.23 eV) band gaps after crystallization. Electrical conductivity of CuCr0.93 Mg0.07O2 thin films ranged 0.6–1 S cm−1 and hole concentration ∼2×1019 cm−3 determined from Seebeck analysis. Temperature dependence of conductivity exhibit activation energies ∼0.11 eV in 300–470 K and ∼0.23 eV in ⩾470 K region ascribed to activated conduction and grain boundary trap assisted conduction, respectively. Heterojunction diodes of the structure Au/n-(ZnO)/p-(CuCr0.93Mg0.07O2)/SnO2 (TCO) were fabricated which show potential for transparent wide band gap junction device.