  High gain photoconductive devices find wide spread applications in low
intensity light detection. Ultra-thin layered materials have recently attracted
a lot of attention from researchers in this regard. However, in general, a
large operating voltage is required to obtain large responsivity in these
devices. In addition, the characteristics are often confounded by substrate
induced trap effects. Here we report multi-layer SnSe2 based photoconductive
devices using two different structures: (1) SiO2 substrate supported
interdigitated electrode (IDE), and (2) suspended channel. The IDE device
exhibits a responsivity of ~ 10^3 A/W and 8.66x10^4 A/W at operating voltages
of 1 mV and 100 mV, respectively - a superior low voltage performance over
existing literature on planar 2D structures. However, the responsivity reduces
by more than two orders of magnitude, while the transient response improves for
the suspended device - providing insights into the critical role played by the
channel-substrate interface in the gain mechanism. The results, on one hand,
are promising for highly sensitive photoconductive applications consuming
ultra-low power, and on the other hand, show a generic methodology that could
be applied to other layered material based photoconductive devices as well for
extracting the intrinsic behavior.
