Following the rise
of interest in the properties of transition
metal dichalcogenides, many experimental techniques were employed
to research them. However, the temperature dependencies of optical
transitions, especially those related to band nesting, were not analyzed
in detail for many of them. Here, we present successful studies utilizing
the photoreflectance method, which, due to its derivative and absorption-like
character, allows investigating direct optical transitions at the
high-symmetry point of the Brillouin zone and band nesting. By studying
the mentioned optical transitions with temperature from 20 to 300
K, we tracked changes in the electronic band structure for the common
transition metal dichalcogenides (TMDs), namely, MoS
2
,
MoSe
2
, MoTe
2
, WS
2
, and WSe
2
. Moreover, transmission and photoacoustic spectroscopies were also
employed to investigate the indirect gap in these crystals. For all
observed optical transitions assigned to specific
k
-points of the Brillouin zone, their temperature dependencies were
analyzed using the Varshni relation and Bose–Einstein expression.
It was shown that the temperature energy shift for the transition
associated with band nesting is smaller when compared with the one
at high-symmetry point, revealing reduced average electron–phonon
interaction strength.