  Low cost, easily integrable photodetectors (PDs) for silicon (Si) photonics
are still a bottleneck for photonic integrated circuits (PICs), especially for
wavelengths above 1.8 ${\mu}$m. Multilayered platinum diselenide (PtSe$_2$) is
a semi-metallic two-dimensional (2D) material that can be synthesized below
450${\deg}$C. We integrate PtSe$_2$ based PDs directly by conformal growth on
Si waveguides. The PDs operate at 1550 nm wavelength with a maximum
responsivity of 11 mA/W and response times below 8.4 ${\mu}$s. Fourier
transform infrared spectroscopy (FTIR) in the wavelength range from 1.25
${\mu}$m to 28 ${\mu}$m indicates the suitability of PtSe$_2$ for PDs far into
the infrared wavelength range. Our PtSe$_2$ PDs integrated by direct growth
outperform PtSe$_2$ PDs manufactured by standard 2D layer transfer. The
combination of IR responsivity, chemical stability, selective and conformal
growth at low temperatures, and the potential for high carrier mobility, make
PtSe$_2$ an attractive 2D material for optoelectronics and PICs.
