Impurity levels in p-type layered semiconductor InSe doped with Hg

Photoluminescence (PL) and Hall effect measurements have been made on Hg-doped p-type InSe. A broad emission band at 1.237 eV (77 K) is mainly observed on the PL spectra of samples doped with Hg and, in the range 0.02 to 0.1 at%, the PL intensity increases with increasing Hg concentration. From the temperature dependences of the PL intensity and peak energy position, we show that the 1.237 eV emission band is due to the transition between a shallow donor level and a deep acceptor level, at 0.07 eV above the valence band. The dominant acceptor level in the carrier transport measurements shows the same energy position as the radiative recombination center.