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Study of photocarriers lifetime distribution in a-Si:H via magneto-photocurrent and magneto-photoluminescence

Advanced Optical Materials

We have investigated the magneto-photoluminescence (MPL) of localized photocarriers and magneto-photoconductivity (MPC) of delocalized photocarriers in amorphous hydrogenated silicon (a-Si:H) films and devices, respectively. Both MPL(B) and MPC(B) field responses are caused by mixing of spin sublevels in the photogenerated exchange-coupled electron-hole (e-h) pairs that alters their recombination and dissociation rates. The spin mixing occurs by a combination of hyperfine interaction (HFI) between spin ½ photocarriers and neighboring 29Si and hH1H nuclei, and the Dg mechanism which originates from a difference in the Land? g-factors of electrons and holes. The existing disorder in a-Si:H films leads to dispersive field response that is described by a unique dispersive parameter a < 1, from which the e-h lifetime distribution, g(t) is obtained. The mean e-h lifetime was found to be ~12 ns for the high-energy, relatively delocalized photocarriers generating the photocurrent, as compared to ~200 ps for the lower energy, trapped e-h pairs which yield photoluminescence. We have also studied the MPL(B) and MPC(B) responses in a-Si:H subjected to prolonged illumination that causes Staebler-Wronski type degradation, and subsequent annealing. We found illumination-induced photocarrier localization that enhances the HFI component, which dramatically decreases upon annealing; this method can assess optoelectronic device degradation.

Adv. Optical Mater. 2200499 (2022)
http://dx.doi.org/DOI: 10.1002/adom.202200499