Urbach tail and electric field influence on optical properties of InSe and InSe:Er single crystals

InSe and InSe:Er single crystals were grown by using the Bridgman-Stockbarger method. The absorption measurements were carried out for voltage U=0 and U=30 V states of InSe and InSe:Er samples in the temperature range of 10-320 K with a step of 10 K. The absorption edge shifted towards longer wavelengths and the intensity of the absorption spectra decreased under a 5.90 kV/cm electric field. The same binding energy values for InSe and InSe:Er were calculated as 22.2 and 14.2 meV at U=0 and U=30 V, respectively. The steepness parameters and Urbach energies for InSe and InSe:Er samples increased with increasing sample temperature in the range of 10-320 K. An applied electric field caused a shift and a decrease of the intensity of the absorption spectra and an increase in the Urbach energy and steepness parameters. The shift of the absorption edge can be explained on the basis of the Franz-Keldysh effect or thermal heating of the sample under the electric field.