A study was made of recombination processes, in high-quality (intrinsic) and light-soaked hydrogenated amorphous material, by using the optically-detected electron spin resonance technique. A time-domain detection scheme was used, instead of the usual lock-in technique, to record the optically detected electron spin resonance line-shapes. This minimized the usual interference between the so-called enhancing and quenching signals. By monitoring the photoluminescence below 1.1eV in intrinsic samples, an almost symmetrical enhancing signal (g = 2.008) was observed which was related to the radiative recombination of spin pairs in shallow band-tail states, as well as an asymmetrical quenching signal (g = 2.005) which was related to the non-radiative recombination of spin pairs in deep band-tail states. A quenching signal at half-field (with g approximately equal to 4) was also observed. The light-soaked sample exhibited an additional signal (g = 2.006) which was related to the dangling bonds. The photoluminescence excitation energy was varied from above to below the optical gap in order to study possible changes in the recombination process. It was found that the optically detected electron spin resonance line-shapes were essentially the same for excitation energies above 1.5eV, while subtle changes occurred at lower energies. However, the signal intensity depended strongly upon the excitation energy, for a given electron-hole pair generation rate.

D.Mao, P.C.Taylor: Journal of Non-Crystalline Solids, 1995, 190[1-2], 48-57