Effect of illumination on noise and some other characteristics of p-n junctions in InSb

Spectra of low-frequency (f = 20 Hz-20 kHz) noise in InSb p-n junctions are investigated at different voltage biases and under different illumination intensities at T = 77°K.

It is found that fluctuations of ohmic leakage current are the main source of the current noise in the dark. Fluctuations of conduction of the space charge region (SCR) are observed only at sufficiently large forward biases. Under illumination fluctuations of the photocurrent make the essential contribution to the excess noises. It is shown that these fluctuations are generated in SCR and their peculiarities depend not only on the value of voltage bias but also on the level of illumination L. A variety of other characteristics of p-n junction are found to be conditioned by illumination level as well: with increasing L the photoelectric efficiency of the diode decreases, and an increase takes place in the equivalent differential conductivity of SCR as well as in the forward current measured at constant voltage biases on the p-n junction. Such changes may be explained either by a decrease of the carrier life-time in SCR or by an increase of the width of SCR.

Arguments are adduced supporting the supposition that excess fluctuations of conductivity of SCR arise only in some regions of SCR which are characterized by the specific mechanism of current conduction.