Temperature Dependence of Two‐Dimensional Optical Energy Gap for Germanium Selenide Single Crystals

The interband absorption coefficient of GeSe single crystals near the fundamental absorption edge is analyzed on the basis of a two‐dimensional model and is found to correspond to an indirect forbidden transition. The optical energy gap at room temperature is found to be (1.066 ± 0.011) and (1.078 ± 0.010) eV for the a ‐ and c ‐crystallographic axes, which lie in the plane of cleavage. The temperature dependence of the two‐dimensional optical energy gap is studied from room temperature to near liquid nitrogen temperature. This dependence is found to be linear in the range from 96 to 250 K with a negative temperature coefficient d E g /d T equal to −0.48 and −0.46 meV per K for the a ‐ and c ‐axes, respectively. The results are compared with those obtained on basis of three dimensional model and agreement is found to be within the limits of experimental error.