Shot noise behavior of planar Mo/n-Si/Mo photodetector structure in avalanche mode

Low-frequency (3 to 50 kHz) shot noise behavior of planar metal/semiconductor/metal photodetector (MSM-PD) structure operating under pre avalanching and avalanching conditions has been observed. The structure examined is Mo/n-Si/Mo structure with electrode separation of 20 μm. In higher voltages applied, both device current and its photocurrent component showed a rapid increase at a critical bias voltage due to onset of avalanche multiplication. It was found that the associated shot noise factor Γ² varies in wide range from the order 0f 0.1 at pre-breakdown conditions to three orders of magnitude larger than unity corresponding to simple shot noise by avalanche multiplication. This result implies that the biasing condition for appropriate operation must be satisfied from the view point of signal-to noise ratio (S/N), when one operates this structure with high optical sensitivity. The value of noise factor obtained seems basically expressible by using existing theory with a little smaller exponent of multiplication factor.