  We study the evolution of the band-gap structure in few-layer MoTe$_2$
crystals, by means of low-temperature micro-reflectance (MR) and
temperature-dependent photoluminescence (PL) measurements. The analysis of the
measurements indicate that, in complete analogy with other semiconducting
transition metal dichalchogenides (TMDs), the dominant PL emission peaks
originate from direct transitions associated to recombination of excitons and
trions. When we follow the evolution of the PL intensity as a function of layer
thickness, however, we observe that MoTe$_2$ behaves differently from other
semiconducting TMDs investigated earlier. Specifically, the exciton PL yield
(integrated PL intensity) is identical for mono and bilayer and it starts
decreasing for trilayers. A quantitative analysis of this behavior and of all
our experimental observations is fully consistent with mono and bilayer
MoTe$_2$ being direct band-gap semiconductors, with tetralayer MoTe$_2$ being
an indirect gap semiconductor, and with trilayers having nearly identical
direct and indirect gaps.This conclusion is different from the one reached for
other recently investigated semiconducting transition metal dichalcogenides,
for which only monolayers are found to be direct band-gap semiconductors, with
thicker layers having indirect band gaps that are significantly smaller, by
hundreds of meV, than the direct gap. We discuss the relevance of our findings
for experiments of fundamental interest and possible future device
applications.
