TRAPPING OF PHOTOCARRIERS IN GA-DOPED BI12GEO20 AT 80 K

Data from measurements of optical absorption, photoconductivity, dark conductivity, thermally stimulated conductivity (TSC), and thermoluminescence (TL) on samples of undoped and Ga-doped, Czochralski-grown Bi 12GeO20 single crystals are reported. The photoconductivity is n type, and the dark conductivity is p type. Undoped BGO exhibits a broad, band-edge absorption due to the optical excitation of electrons to the conduction band which gives the samples a yellow coloration. This absorption is reduced by the addition of Ga which acts as a compensating acceptor. When illuminated with light into this absorption band, but with photons of energy less than the band gap, photoexcitation of electrons occurs. These become trapped, inducing additional absorption and photoconductivity bands and TSC signals, but not TL. Excitation with photons of energy greater than the band gap induces both TSC and TL. Examination of the TSC and TL signals as a function of excitation wavelength allows the distinction between electron and hole trapping states for which trapping parameters have been determined. In addition, dark conductivity reveals three major hole states at energies of ∼Ev+1.41, ∼Ev+0.86, and ∼Ev+0.54 eV. These are believed to be empty donor states. © 1995 American Institute of Physics.