ELECTRICAL-CONDUCTIVITY AND NEAR-INFRARED ABSORPTION OF CUGASE2 THIN-FILMS

Near-infrared absorption spectra at room temperature in the photon ene rgy range hv approximate to 0.4 to 1.5 eV and electrical conductivity (sigma) in the temperature range 300 to 450 K are measured for p-type CuGaSe2 thin films. Two acceptor levels with ionization energies E(1) (240, 270 meV) and E(2) (80, 90 meV) are found. The ionization energy of accepters is also obtained from optical absorption measurements as 280 meV. Free carrier absorption below 0.5 eV is observed in which the absorption coefficient alpha increases as the third power of the wave length lambda and the carrier concentration dependence of alpha is sup erlinear rather than linear in this region of photon energy. This abso rption is associated with the ionized impurity scattering mechanism. A n absorption band at hv approximate to 0.75 eV is also found, its peak energy and value of alpha depend on the carrier concentration. This b and may be due to the transition from a lower lying valence band to an upper one.