Calorimetric Investigation of Relaxation Processes in Disordered Semiconductors

Abstract

AbstractThe comparative study of relaxation processes in amorphous hydrogenated (a- Si:H) and porous silicon (PS) by use of differential scanning calorimetry (DSC) measurements is presented. Films of a-Si:H were deposited by RF glow discharge of two gas mixtures (10% SiH4+ 90% H2) and (5% SiH4 + 95% He). PS films have been prepared by electrochemical etching of 1Ω-cm (p- PS) and of 0.01Ω-cm (p+ PS) ptype Si substrates. The DSC traces were recorded during the heating of samples at a constant rate of 10°C/min from 20 to 5700C in an Ar atmosphere. All investigated samples present a low temperature exothermic effect with a maxima within 120-2800C. At higher temperatures (T>3000C) a second exothermic effect is observed for a-Si:H films prepared from both hydrogen and helium diluted silane mixtures while two endothermic effects are observed for PS samples. Analysis of the low temperature exothermic effects has been performed, and focussed on the relaxation of weak Si-Si bonds which are the features of both amorphous hydrogenated and porous silicon. It was shown that the endothermic effect connected with hydrogen effusion from PS at higher temperatures is compensated by exothermic structural rearrangement in the case of a-Si:H.