Specific detectivity
Specific detectivity, or D*, for a photodetector is a figure of merit used to characterize performance, equal to the reciprocal of noise-equivalent power (NEP), normalized per square root of the sensor's area and frequency bandwidth (reciprocal of twice the integration time). Specific detectivity is given by D ∗ = A Δ f N E P {\displaystyle D^{*}={\frac {\sqrt {A\Delta f}}{NEP}}} , where A {\displaystyle A} is the area of the photosensitive region of the detector, Δ f {\displaystyle \Delta f} is the bandwidth, and NEP the noise equivalent power (in units of W / H z {\displaystyle W/{\sqrt {Hz}}} ).