Band and subband absorption of Se/CdSe amorphous multilayers

The band and subband absorption in single CdSe layers and pnpn type Se/CdSe multilayers (MLs) has been measured by the constant photocurrent method. From studies on the MLs' band absorption the conclusion is reached that the photoconductivity of the CdSe sublayers decreases with both decreasing thickness and evaporation rate. An increase of the Urbach edge parameter E u from 57 to 80 meV has been obtained on decreasing the CdSe sublayer thickness or on increasing the deposition rate. A ‘shoulder’ has been observed in the MLs' absorption measured in the lowest energy region. Indirect transitions from the Se valence band to the CdSe conduction band have been proposed as a possible explanation of the shoulder absorption. The observed change in the shoulder position with changing CdSe sublayer thickness has been attributed to quantum size effects.