  Current optical communication system operating at 1.55 {\mu}m wavelength band
may not be able to continually satisfy the growing demand on the data capacity
within the next few years. Opening a new spectral window at around 2 {\mu}m
wavelength with recently developed hollow-core photonic band gap fiber and
thulium-doped fiber amplifier is a promising solution to increase the
transmission capacity due to the low loss and wide bandwidth properties of
these components at this wavelength. However, as a key component, the already
demonstrated high speed photodetectors at 2 {\mu}m wavelength are still not
comparable with those at 1.55 {\mu}m wavelength band, which chokes the
feasibility of the new spectral window. In this work, we, for the first time,
demonstrated a high speed uni-traveling carrier photodiode for 2 {\mu}m
applications with InGaAs/GaAsSb type-II multiple quantum wells as the
absorption region, which is lattice matched to InP. The device shows a 3dB
bandwidth of 25 GHz at -3 V bias voltage and is, to the best of our knowledge,
the fastest photodiodes among all group III-V and group IV photodetectors
working in 2 {\mu}m wavelength range.
