Absorption Coefficient of a Semiconductor Thin Film from Photoluminescence

The photoluminescence of a semiconductor is a very sensitive means to determine its absorption coefficient, using Planck's generalized law. The standard method (suitable only for self-supported thick samples like wafers) is here extended to multilayer thin films, by using the transfer-matrix method to include the effects of the substrate and optional front layers. This technique allows one to circumvent parasitic absorption from the substrate, and thus to determine accurately down to very low values, for investigation of deep band tails. Accounting for the substrate effect is important for a clear understanding of how a solar cell is functioning, and how to improve it.