Transparent and conducting ZnO(:Al) films deposited by simultaneous RF- and DC-excitation of a magnetron

RF magnetron sputtering of zinc oxide films (ZnO:Al and ZnO) is mostly used for the deposition of the window and contact layer for heterojunction thin film solar cells. A drawback of this sputtering technique is the small deposition rate. This is caused by the low DC voltage that develops at the target, since the sputtering rate in the energy range below 1 keV depends linearly on the acceleration voltage in the cathode fall. In order to increase the target voltage, a simultaneous excitation by RF (13.56 MHz) and DC has been used. Excitation by DC increases the deposition rate up to a factor of 1.5. On the other hand, RE-excitation decreases the specific resistance significantly. The reason for the better electrical properties of RF-sputtered films is the higher energy of the ions (up to a factor of 2.5) that bombard the substrate during the deposition. (C) 1998 Elsevier Science S.A.