Direct Experimental Evidence for Molecular Hydrogen in Amorphous Si: H

Abstract

Molecular hydrogen in amorphous Si: H films prepared by glow discharge is detected calorimetrically at low temperatures from the heat release associated with the ortho-to-para conversion. The ${\mathrm{H}}_2$ concentration is much higher in samples prepared at 250°C (6.4 × ${10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$) than in those prepared at room temperature (2.4 × ${10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$). These results support a recent model of ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ nuclear spin relaxation via interaction with ${\mathrm{H}}_2$ molecules in $a$-Si: H and, in addition, give new insight into the structure of $a$-Si: H.