Matrix controlled equilibrium between the various H sites in annealed sputtered a-Si:H

Abstract

The authors have measured the total hydrogen concentration (H) and the hydrogen concentration in SiH (H1), SiH2 (H2) and other sites (H'). From uniform depth profiles of total hydrogen concentration they conclude that hydrogen concentration is not limited by diffusion. They report here the variations of (H), (H1), (H2) with annealing temperature for substrate temperature Ts=150 degrees C, 190 degrees C and 250 degrees C and deposition rates ' nu ' ranging from 20 to 120 AA min-1. The authors lose hydrogen only above the annealing temperature at which hydrogen saturates the Si matrix; (H) saturates at a value (Hs) which is independent of Ts and nu , at each annealing temperature TA. Annealing induces simultaneous variations of the hydrogen concentration on all the sites. All these results are interpreted by a model according to which the hydrogen is linked to the a-Si matrix defects, filling first the deeper ones and then the more shallow defects. According to this model the total hydrogen concentration is limited by the total Si matrix defect concentration.