Spin-dependent hole diffusion in a-Si: H

Abstract

Two-beam photoconductivity (PC), spin-dependent photoconductivity (SDPC), and light-induced ESR (LESR) have been measured on undoped a-Si: H with low spin densities, N _s ≤ 10¹⁶ cm⁻³. Below T = 160 K, PC is quenched by irradiation with photon energies less than 1·5 eV. Both LESR and SDPC spectra change correspondingly. In LESR the broad signal due to trapped holes is strongly quenched, whereas the narrow signal due to trapped electrons and dangling bonds decreases only a little. The SDPC spectrum, also containing a broad and a narrow line, changes in the opposite way: the broad line remains almost constant and the narrow signal increases. The results are explained in terms of recombination of trapped electrons with trapped holes via neutral dangling bonds, the rate-determining step being the diffusion of trapped holes towards doubly occupied dangling bonds. Hole diffusion is further identified in spin-dependent dark conductivity measurements on boron-doped a-Si: H.