Study of Time-Resolved Optically Detected Magnetic Resonance in Semiconductors

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We have set up the apparatus for time-resolved optically detected magnetic resonance (TRODMR) measurements operating at 9.6 GHz and 2 K. A dye laser pumped by either a pulsed <N_2> laser of 5 ns or a pulsed excimer laser of 10 ns was used as a pulsed excitation source. Using such equipment, we have carried out TRODMR experiments on a-Si:H, a- <Si_(1-x)N_x> :H and a-Si:H/a- <Si_(1-x)N_x> :H superlattices. The following results and conclusions have been obtained:1. The ODMR signal due to tail electrons in a-Si:H was observed for the first time. Thus, radiative recombination of tail electrons with trapped holes at the A centres and/or the valence band tail was clarified as a function of delay time of the microwave pulse and the gate pulse for the measurement, <t_d> , after a pulsed excitation.2. For a-Si:H/a- <Si_(1-x)N_x> :H superlattices, the confinement effect of electrons and holes in the well layer (a-Si:H) was inferred from the results of relative change in the luminescence intensity at the A centre resonance as a function of <t_d> . For superlattices not containing a number of defects at the interfaces, nonradiative recombination through dangling bonds in thin well layers was found to be suppressed compared to that for a-Si:H bulk films.3. Triplet exciton recombination was investigated by observing the g <Similar or Equal> 4 ODMR signal and the broad g <Similar or Equal> 2 ODMR signal in a-Si:H, a- <Si_(1-x)C_x> :H and a- <Si_(1-x)N_x> :H. From TRODMR experiments, it was concluded that triptet excitons decay with a time constant of <about> 1 ms in a-Si:H. From these investigations, we conclude that TRODMR technique provides a powerful means for elucidating recombination processes and nature of recombination centres in semiconductors.