White Noise in silicon-based planar metal-semiconductor-metal photodiodes

Low-frequency 3-100 kHz shot noise (white noise) emerging from photoinduced current in Mo/n-Si/Mo structures leaving undepleted region has been observed under different bias and optical intensity conditions. The measurements revealed that the current noise observed depends not only on the illumination intensity levels but also on bias voltage. The current noise observed is expressed as S(omega)=2IGamma² and analyzed, where I and Gamma² is the average current and noise factor, respectively. The measurements reveal that Gamma² has strong bias dependence, lying Gamma²~ 0.01 to about unity corresponding to simple shot noise. Such experimental results are explained, stating that the reduction of cross correlation between drift and diffusion currents and autocorrelation of drift current component determining the level of noise occurs with decrease in SCR width bias-dependent. To explain the behavior of observed noise more properly, we propose, in addition to the mechanisms above, that the reduction in autocorrelation effect of each current component plays an important role to decrease the relevant noise to such extremely low levels.