Implication of subband broadening in the quantum well of a-Si:H/a-Ge:H multilayers

The optical absorption, photoluminescence and conductivity of well-defined a-Si:H/a-Ge:H multilayers have been investigated as a function of the a-Si:H barrier width. The optical absorption edge and luminescence peak energy exhibit a similar red-shift with decreasing the a-Si:H barrier width. Also, the decrease of the barrier width causes a reduction in the conductivity activation energy and the corresponding increase in the dark conductivity. These properties are explained partly by the subband broadening in the a-Ge:H quantum well because of the enhanced carrier tunneling probability through the ultrathin a-Si:H barriers and partly by a decrease of hydrogen content in the a-Ge:H well layer.