a-Si:H deposited at high rate on the cathode of a rf-PECVD reactor

Hydrogenated amorphous silicon (a-Si:H) films were deposited in a standard diode-type radio-frequency plasma-enhanced chemical vapor deposition (rf-PECVD) reactor. Larger deposition rates were achieved by replacing the powered electrode plate by a cup-shaped electrode, whose area was larger than that of the grounded substrate holder by a factor of 5. As a result the substrate holder became the cathode and the deposition rate increased by a factor of 10 to similar to 3 nm s(-1). The best properties of cathode samples were obtained at substrate temperatures near 350 degrees C, as opposed to typically 250 degrees C for anode samples. Our results indicate that the ion bombardment occurring on the cathode improves the growth of a-Si:H films at the higher deposition rates observed. Nevertheless, in the as-deposited state, the defect density N(D) and the ambipolar diffusion length L(D) of the cathode samples are inferior compared to anode films. After intense light soaking, however, the properties of anode and cathode samples agree within experimental accuracy. (C) 1998 Elsevier Science B.V. All rights reserved.