Electron and hole diffusion length investigation in CdTe thin films by SPV method

Abstract

The minority carrier diffusion length has been determined on CdTe thin films deposited on Bi or Pb layers by the quasi-rheotaxy technique. The surface photovoltage method (SPV) has been extended to the case of thin films. In order to measure both electron and hole diffusion length, p-CdTe/n-CdTe shallow homojunctions and n-CdS/p-CdTe heterojunctions were prepared. High conductivity CdS films, a few micrometers in thickness, acting as transparent electrodes in the spectral region of the SPV measurements, were grown to induce a depletion region into the p-type CdTe absorber film. Electron diffusion lengths in the range 0.4–1.6 μm were found in films grown at temperatures in the range 246–264°C. A hole diffusion length of about 0.8 μm has been measured in the lead doped n-CdTe base material of the homojunctions which was grown at 320°C.