Influence of the reduced dimensionality on the thermodynamical and electrical properties of photosensitive BiOX (X = Cl, Br, and I) semiconductors

The influence of the layered structure on the temperature dependencies of the specific heat, thermal conductivity, and electric resistivity of photosensitive bismuth oxyhalides BiOX (X = Cl, Br and I) single crystals were investigated in the temperature range 2 K ≤ T ≤ 300 K. The low temperature specific heat data for BiOX demonstrated the presence of two-dimensional behavior with increased anisotropy for the BiOI sample. Moreover, the thermal conductivity values for BiOI are three times higher than for BiOCl and BiOBr, and this observation is consistent with increased anisotropy arising from the contribution of optical out-of-plane phonons. The influence of green (λ = 532 nm) and red (λ = 640 nm) laser excitations on the electrical conductivity properties has been investigated. Each photoconductivity curve reveals transitions from low to high sensitivity. The depletion temperature region for BiOX single crystals corresponds to the peak in temperature dependence of the charge carrier mobility.