Laser-induced doping of aluminum into a cadmium telluride thin film: Electrical and optical properties

Abstract

The electrical properties of cadmium telluride (CdTe) thin films are essentially determined by the doping process; the laser-induced doping method was chosen to dope aluminum (Al) as a donor into CdTe thin films to perform a selective and controllable doping process for multilayer structured photovoltaic devices. The laser-induced doping of Al used a helium-neon (He-Ne) laser (632.8 nm) to expose sputtering-deposited p-type CdTe thin films after they had been annealed at 400 °C for 1 hour. The Auger electron spectroscopy depth profile showed better doping uniformity for longer exposure to the time of He-Ne laser in the doping process. The conductivity of the CdTe thin films was changed from p-type to n-type once the doping of Al was performed. The optical band gap energy of the CdTe thin films decreased from 1.451 eV to 1.418 eV after 10 minutes of Al doping. The average absorbance value of the CdTe thin films improved from 1.58 to 1.72 by doping with Al due to impurity-scattering via the doped Al atoms in the CdTe thin films. The resistivity of the Al-doped CdTe thin films was reduced significantly from the order of 104 Ω-cm to the order of 10−6 Ω-cm after only 1 minute of exposure. The carrier concentration of the CdTe thin films increased to a maximum value of 1.2 × 1021 cm−3 after a 10-minute exposure to the He-Ne laser. The laser-induced doping of Al into CdTe thin films is a very simple and effective method to dope a multilayered thin-film solar cell with a relatively short process time, no wet-process, and selective treatment to control the conductivity type, the optical band gap energy, the absorbance, the carrier concentration, and resistivity of the thin films.