Noise, Time-Constant, and Hall Studies on Lead Sulfide Photoconductive Films

Measurements of the noise in seven lead sulfide photoconductive films over the frequency range 20-16 000 cps show that the noise consists mainly of a $\frac{1}{f}$ component at frequencies below 100 cps, a generation-recombination component between 100 and 10 000 cps and a Nyquist component at higher frequencies. The data are analyzed to give the magnitude, $N_{s0\mathrm{}}(\mathrm{G}-\mathrm{R})$, and the time constant, ${\tau }_n$, of the generation-recombination noise. The signal time constant, ${\tau }_s$, is found by measuring the frequency dependence of the photoconductive response. The product of the majority carrier density and the film thickness, $\mathrm{pd}$, is found from measurement of the Hall voltage. Representative values are $N_{s0\mathrm{}}(\mathrm{G}-\mathrm{R})=4.5\mathrm{}\times {10}^{-9\mathrm{}}$ rms noise $\frac{\mathrm{volts}}{\left[\right(\mathrm{dc}\mathrm{bias}\mathrm{volt}\times {\left(\Delta f\right)}^{\frac{1}{2}}]}$, ${\tau }_n=230\mathrm{}$ μsec, ${\tau }_s=280\mathrm{}$ microseconds, and $pd=3.0\mathrm{}\times {10}^{12}/{\mathrm{cm}}^2$.