Spin-lattice relaxation of paramagnetic states in a-Si:H and a-Ge:H

The electron spin-lattice relaxation times of the three paramagnetic species - dangling bonds (db), conduction band tail electrons (c) and valence band tail holes (v) - have been measured in a-Si:H and a-Ge:H for temperatures between 5 K and 300 K. Additional measurements have been carried out on deuterated, evaporated and annealed samples. The data indicate that the relaxation is dominated by coupling to localized two level systems (TLS) and the times are limited by the average TLS relaxation times. The density of TLS increases with the degree of network disorder.