Chemical spray pyrolysis deposition and characterization of p-type CuCr 1−xMg xO 2 transparent oxide semiconductor thin films

Abstract

A chemical spray pyrolysis technique for deposition of p-type Mg-doped CuCrO 2 transparent oxide semiconductor thin films using metaloorganic precursors is described. As-deposited films contain mixed spinel CuCr 2O 4 and delafossite CuCrO 2 structural phases. Reduction in spinel CuCr 2O 4 fraction and formation of highly crystalline films with single phase delafossite CuCrO 2 structure is realized by annealing at temperatures ⩾700 °C in argon. A mechanism of synthesis of CuCrO 2 films involving precursor decomposition, oxidation and reaction between constituent oxides in the spray deposition process is presented. Post-annealed CuCr 0.93Mg 0.07O 2 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 CuCr 0.93 Mg 0.07O 2 thin films ranged 0.6–1 S cm −1 and hole concentration ∼2×10 19 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-(CuCr 0.93Mg 0.07O 2)/SnO 2 (TCO) were fabricated which show potential for transparent wide band gap junction device.