URBACH-MARTIENSSEN TAILS IN ER-DOPED AND UNDOPED N-TYPE INSE

Optical absorption spectra of InSe:Er and InSe single crystals were in vestigated. The exponentially increasing absorption tail was explained as an Urbach-Martienssen (U-M) tail for both InSe:Er and InSe samples in the temperature range 100-340 K. Characteristic Urbach's parameter s such as steepness parameter sigma(T), Urbachs energy (E-u = k(B)T/si gma) and effective phonon energy (hv(p)) were obtained as a function o f temperature. The Urbach's energy of the Er-doped sample decreased as a function of temperature in the investigated temperature region. Suc h a decrease of the Urbach's energy can be explained to be due to the reduction of the electronic distortion caused by the compositional dis order associated with the planar defects in the crystal lattice in InS e by the Er doping procedure. (C) 1998 Elsevier Science B.V. All right s reserved.