Growth and temperature dependence of optical properties of Er doped and undoped n-type InSe

n-InSe and Er doped n-InSe (n-InSe:Er) single crystals were grown by the modified Bridgman-Stockbarger method. The prepared InSe and InSe:Er single crystal ingots were 12 mm in diameter and about 80 mm in length. The ingots had no cracks or voids on the surface. The absorption measurements were carried out for n-InSe, and n-InSe:Er samples in the temperature range of 10-320 K. Binding energies of n-InSe and n-InSe:Er were calculated to be 20.5 meV and 21.0 meV respectively. The direct band gaps were estimated to be 1.339 eV, 1.289 eV and 1.256 eV in n-InSe and were 1.338 eV, 1.288 eV and 1.253 eV in n-InSe:Er at 10 K, 200 K and 300 K, respectively. E-o (1.247 eV) obtained from the Urbach rule is nearly equal to the energy gap of n-InSe at 300 K.