Sub-bandgap analysis of boron doped InSe single crystals by constant photocurrent method

Sub-bandgap absorption properties of indium selenide doped with boron atoms within a range of [B] = 0-1.8 at.% have been investigated. From the absorption coefficient spectra measured by using constant photocurrent method (CPM) at 300 K, we observed that the disorder in the structure increases. The calculated Urbach parameters, quantifying the disorder, vary from 17 to 53 meV, as [B] is increased from 0 to 1 at.%. Also the calculated optical gaps decrease from 1.28 eV to 1.17 eV for the same range of [B]. From temperature dependent dark conductivity measurements, the characteristic activation energies are calculated to range from 0.25 to 0.18 eV for vertical (to c-axis) direction; to stay almost constant for parallel (c-axis) direction. At a temperature of 12 K, the absorption coefficient spectra by using CPM and the radiative recombination spectra by photoluminescence (PL) have been taken for the samples with [B] = 0 and 0.5 at.%. Three main PL bands are observed at photon energies of ∼1.24, 1.306 and 1.337 eV. The PL bands are interpreted by corresponding absorption bands detected at 12 K and at the photon energies of ∼1.24, ∼1.31 and ∼1.35 eV.