We have used light-induced electron spin resonance (LESR) and photoluminescence (PL) to examine the energetic and spatial distribution of non-equilibrium carriers in a-Si:H excited with monochromatic light of 1.16 to 1.96 eV at T = 20 K. The LESR spectra and the observation of intrinsic PL for excitation with hν < 1.4 eV reveal that efficient generation of both electrons and holes occurs by defect absorption. However, the quantum efficiency of the intrinsic PL is smaller by about one order magnitude while that of the defect PL is larger by a factor of 5 compared to excitation with hν > 1.5 eV. This is attributed to the fact that not only carrier creation but also most of the recombination occurs through the defect levels. Our LESR data suggest a very similar ratio of band-tail electrons and holes, namely 0.4, for excitation with 1.16 and 1.96 eV photons, respectively. We believe that this result argues against the existence of a significant density of charged defects in undoped a-Si:H films.
|Number of pages||4|
|Journal||Journal of Non-Crystalline Solids|
|Issue number||PART 1|
|Publication status||Published – 2 Dec 1993|