Optical studies of transition metal dichalcogenide layer crystals at high pressures

Abstract

The shift in the position of a number of exciton peaks seen in the spectra of the layer type transition metal dichalcogenides has been measured in a hydrostatic pressure apparatus capable of reaching pressures up to 6 kilobars, in the temperature range 80°K to 295°K. For the Group 6 materials MoS₂ and WSe₂, the magnitude and sign of the pressure coefficients for the AB excitons and the A'B’ excitons are different. There are also differences in the behaviour of the 2H and 3K polytypes. The results show that layer-layer interactions must be considered in calculations of the electronic band structure. The pressure coefficients of the Group 5 metal NbS₂ and the Group 4 insulators HfS₂, HfSe₂ and ZrS₂ have also been determined and are compared with those of the Group 6 semiconductors.