Depth profiling of vacancy-type defects in homogenous and multilayered a-Si films by positron beam Doppler broadening

Positron annihilation measurements have been carried out on a-Si:H thin films deposited by plasma enhanced chemical vapour deposition at a high rate and on pin/pin double-junction diodes prepared conventionally by means of the variable-energy positron beam Doppler-broadening technique. The depth profiles of microvoids in films grown under different conditions have been determined. We found a smaller void fraction in the surface region of all films compared to the interior. The depth profiles of microvoid-like defects in the a-Si:H films were extracted by use of the VEPFIT programme. Variable-energy positron-annihilation spectroscopy results on the diode show that the interfaces are of good quality except for the Au/n interface, consistent with the diode characteristic. © 1998 Elsevier Science B.V. All rights reserved.