Deposition and characterization of Cd1-xMgxTe thin films grown by a novel cosublimation method

Photovoltaic cells utilizing the CdS/CdTe structure have improved substantially in the past few years. Despite the recent advances, the efficiency of CdS/CdTe cells is still significantly below their Shockley-Queisser limit. CdTe based ternary alloy thin films, such as Cd1-xMgxTe (CMT), could be used to improve efficiency of CdS/CdTe photovoltaic cells. Higher band gap Cd1-xMgxTe films can be the absorber in top cells of a tandem structure or an electron reflector layer in CdS/CdTe cells. A novel cosublimation method to deposit CMT thin films has been developed. This method can deposit CMT films of band gaps ranging from 1.5 to 2.3 eV. The cosublimation method is fast, repeatable, and scalable for large areas, making it suitable for implementing into large-scale manufacturing. Characterization of as-deposited CMT films, with x varying from 0 to 0.35, reveals a linear relationship between Mg content measured by energy dispersive x-ray spectroscopy and the optical band gap. Glancing angle x-ray diffraction (GAXRD) measurements of Cd1-xMgxTe films show a zinc-blende structure similar to CdTe. Furthermore, increasing Mg content decreases the lattice parameter and the grain size. GAXRD shows the films are under mild tension after deposition. (C) 2014 American Vacuum Society.