OPTICALLY DETECTED ESR STUDIES OF RECOMBINATION PROCESSES IN A-SI-H

A study of recombination processes in high-quality (intrinsic) and lig ht-soaked hydrogenated amorphous silicon (a-Si:H) using the technique of optically detected electron spin resonance (ODESR) is reported. A t ime-domain detection scheme is employed, instead of the conventional l ock-in technique, to record the ODESR lineshapes, which effectively mi nimizes the well-known interference between the 'enhancing' and 'quenc hing' 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 to non- radiative recombination of spin pairs in deep band tail states are obs erved. A quenching signal at half-field (g similar or equal to 4) is a lso observed. The light-soaked sample exhibits an additional signal (g = 2.006) which is related to the dangling bonds. The PL excitation en ergy, E(x), is varied from above to below the optical gap to study pos sible changes in the recombination processes. It is found that the ODE SR lineshapes are essentially the same for E(x) > 1.5 eV and some subt le changes occur for E(x) <1.5 eV. The signal intensity, however, depe nds strongly on the excitation energy for a constant electron-hole pai r generation rate.