  In integrated photonics, specific wavelengths are preferred such as 1550 nm
due to low-loss transmission and the availability of optical gain in this
spectral region. For chip-based photodetectors, layered two-dimensional (2D)
materials bear scientific and technologically-relevant properties leading to
strong light-matter-interaction devices due to effects such as reduced coulomb
screening or excitonic states. However, no efficient photodetector in the
telecommunication C-band using 2D materials has been realized yet. Here, we
demonstrate a MoTe2-based photodetector featuring strong photoresponse
(responsivity = 0.5 A/W) operating at 1550nm on silicon photonic waveguide
enabled by engineering the strain (4%) inside the photo-absorbing
transition-metal-dichalcogenide film. We show that an induced tensile strain of
~4% reduces the bandgap of MoTe2 by about 0.2 eV by microscopically measuring
the work-function across the device. Unlike Graphene-based photodetectors
relying on a gapless band structure, this semiconductor-2D material detector
shows a ~100X improved dark current enabling an efficient noise-equivalent
power of just 90 pW/Hz^0.5. Such strain-engineered integrated photodetector
provides new opportunities for integrated optoelectronic systems.
