  Highly sensitive and fast photodetector devices with CdSe quantum nanowires
as active elements have been developed exploiting the advantages of electro-
and wet-chemical routes. Bismuth nanoparticles electrochemically synthesized
directly onto interdigitating platinum electrodes serve as catalysts in the
following solution-liquid-solid synthesis of quantum nanowires directly on
immersed substrates under mild conditions at low temperature. This fast and
simple preparation process leads to a photodetector device with a film of
nanowires of limited thickness bridging the electrode gaps, in which a high
fraction of individual nanowires are electrically contacted and can be exposed
to light at the same time. The high sensitivity of the photodetector device can
be expressed by its on/off-ratio or its photosensitivity of more than 107 over
a broad wavelength range up to about 700 nm. The specific detectivity and
responsivity are determined to D* = 4*10^13 Jones and R = 0.32 A/W,
respectively. The speed of the device reflects itself in a 3 dB frequency above
1 MHz corresponding to rise and fall times below 350 ns. The remarkable
combination of a high sensitivity and a fast response is attributed to
depletion regions inside the nanowires, tunnel-junction barriers between
nanowires, as well as Schottky contacts at the electrodes, where all these
features are strongly influenced by the number of photo generated charge
carriers.
