Photoluminescence quenching by electric fields in hydrogenated amorphous silicon

The decrease of photoluminescence (PL) intensity at low temperature was measured as a function of external fields (up to 3*10⁵ V/cm) in hydrogenated amorphous silicon (a-Si:H). The results are discussed within the framework of the recombination of geminate pairs together with basic physical phenomena such as carrier separation during thermalization trapping of photoexcited carriers in band tails, and possible subsequent reemission or tunneling out of traps. It is concluded that separation of carriers during relaxation in extended and flat tail states is the dominant process for the field quenching of PL intensity. But other processes such as Poole-Frenkel emission and tunneling out of traps cannot be ruled out totally. The basic idea of carrier separation is supported by consistent values for the average mobility from both the quenching of PL intensity with electric fields and the concomitant energy shift of the maximum in the PL spectra.