Structural and physical effects of Mg-doping on p-type CuCrO2 and CuAl0.5Cr0.5O2 thin films

Abstract

Magnesium doped thin films of CuCrO₂ and CuAl_0.5Cr_0.5O₂, both exhibiting delafossite structure, were synthesized via sol–gel processing. The influence of the dopant on the phase development during the subsequent 2-step annealing procedure was monitored by X-ray diffraction. Systematic variation of the dopant concentration between 2.5 and 15% revealed that the Mg inhibits crystallization and stabilizes spinel phases against thermal decomposition, whereby the amount of impurities in the delafossite films is increased. Nevertheless the p-type conductivity and surprisingly the transmittance of the CuCrO₂ films were improved by Mg doping by two orders of magnitude and 16%, respectively. On the contrary the performance of the CuAl_0.5Cr_0.5O₂ films hardly profits from Mg doping. The Seebeck-coefficients of this system even imply a decreasing charge carrier density with increasing dopant concentration, which can only be interpreted as an expulsion of the native defects acting as strong intrinsic doping. The band gap of both oxides remains constant, however.