Optically detected ESR studies of recombination processes in a-Si:H

Abstract

A study of recombination processes in high-quality (intrinsic) and light-soaked hydrogenated amorphous silicon (a-Si:H) using the technique of optically detected electron spin resonance (ODESR) is reported. A time-domain detection scheme is employed, instead of the conventional lock-in technique, to record the ODESR lineshapes, which effectively minimizes the well-known interference between the ‘enhancing’ and ‘quenching’ signals. Monitoring the photoluminescence (PL), below 1.1 eV, in the intrinsic sample, a nearly symmetric enhancing signal ( g = 2.008) related to radiative recombination of spin pairs in shallow band-tail states and an asymmetric quenching signal ( g = 2.005) related non-radiative recombination of spin pairs in deep band tail states are observed. A quenching signal at half-field ( g ≌ 4) is also observed. The light-soaked sample exhibits an additional signal ( g = 2.006) which is related to the dangling bonds. The PL excitation energy, E x, is varied from above to below the optical gap to study possible changes in the recombination processes. It is found that the ODESR lineshapes are essentially the same for E x > 1.5 eV and some subtle changes occur for E x < 1.5 eV. The signal intensity, however, depends strongly on the excitation energy for a constant electron-hole pair generation rate.