Thermalization gap of a-Si:H well layer in a-Si:H/a-Si3N4:H multilayers

The excitation energy dependence of the peak energy of the luminescence from a-Si:H well layers with thicknesses of 40, 5, 2.5, 1.3 and 0.5 nm in a-Si:H/a-Si3N4:H multilayers has been investigated at 15 K. The dependence shows that the luminescence in a-Si:H has the Stokes shift of 0.4 eV and the thermalization gap of the a-Si:H well layer obtained from the excitation energy dependence increases from 1.65 to 2.15 eV with decreasing well layer thickness. The dependence of the thermalization gap on the well layer thickness is explained from the hopping thermalization with the hopping length of about 2.5 nm at band tail localized states.