Electron doping of ALD-grown ZnO thin films through Al and P substitutions

Several series of Al- and P-doped ZnO thin films have been deposited with atomic layer deposition at different temperatures using diethyl zinc, trimethyl aluminum, trimethyl phosphate, and H2O as the precursors. The optimal deposition temperature range is found at 160–220 °C where the film growth is stable and well-crystallized films with low resistivity are obtained. The effect of the dopant content on the charge carrier density of the films is evaluated based on optical reflectivity, Seebeck coefficient, and electrical resistivity data for the films. Both dopants are found to be effective in controlling the carrier density of ZnO; systematic increase in carrier density is demonstrated for Al-doping up to 2 at.% and for P-doping up to 5 at.%. The conductivity of the as-deposited films remains n-type.