Growth and absorption properties of Dy-doped and undoped p-type TlGaSe2

Undoped p-TlGaSe2 and Dy-doped p-TlGaSe2 (p-TlGaSe2:Dy) single crystals were grown by the Bridgman-Stockbarger method. Absorption spectra were measured on freshly cleaved (001) surfaces. The freshly cleaved crystals had a mirror-like surface and there was no need for mechanical treatment. The absorption measurements were carried out in p-TlGaSe2 and p-TlGaSe2:Dy samples in the temperature range 10-320 K with a step of 10 K. The phonon energies calculated in p-TlGaSe2 and p-TlGaSe2:Dy are 23.0 meV and 21.0 meV, respectively. The direct band gaps of p-TlGaSe2 and p-TlGaSe2:Dy are 2.279 eV and 2.294 eV at 10 K, respectively. There is an abrupt change for the energy peak for p-TlGaSe2 in the temperature ranges 105-120 K, 240-250 K, and for p-TlGaSe2:Dy in the temperature ranges 100-110 K, 240-260 K.