Photoluminescence determination of minority-carrier kinetics in semiconductors

Abstract

A new optical technique has been developed to measure the electronic transport properties of semiconductors. It requires only a semiconductor for which the absorption spectrum is known and for which the luminescence can be observed. On the high-energy side of the band-band luminescence peak, the luminescent intensity is proportional to the logarithm of the quasi-Fermi-level separation $\mu$ and independent of any other details of the semiconductor's electronic properties. On the low-energy side of the peak, the intensity is additionally proportional to $\alpha \mathrm{}\left(E\right)l$, where $l$ is the minority-carrier diffusion length, and $\alpha \mathrm{}\left(E\right)\mathrm{}$ is the material's absorption coefficient. The combination of $\mu$ and $l$ with an estimate of the equilibrium carrier density gives the minority-carrier lifetime. The value of $\mu$ reflects both surface and bulk recombination rates; manipulation of the experimental parameters allows them to be separated. This technique and its limitations have been demonstrated with measurements on thin polycrystalline films of CdS and on wafers of ${\mathrm{Zn}}_3$ ${\mathrm{P}}_2$ and CdTe.