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UBC Theses and Dissertations

Signal and noise characteristics of photovoltaic P-N junction diodes Galbraith, Donald Stewart

Abstract

The noise characteristics of ideal photovoltaic p-n junction diodes are discussed and investigated. The hypothesis is advanced that the open-circuit noise from an illuminated ideal diode is entirely due to the shot noise of the various current contributions. Theoretical justification for this theory is developed and the parameter t, the effective noise temperature ratio, is introduced. The possible reasons for excess noise in p-n photo-diodes observed in earlier experiments are suggested. The dc and ac behavior of a real diode chosen to be very nearly ideal in its dc characteristic is found to be consistent with existing diode theory. The various parameters appropriate to the device are evaluated. Equipment for noise measurement is selected and a comparison technique adopted. This method avoids many of the possible errors inherent in an absolute measurement and allows an equivalent noise resistance resolution of about 200 ohms at room temperature in the 200 cs bandwidth measured. The open-circuit noise of the selected diode is measured at 20 and 30 kc as a function of illumination and the results interpreted in terms of the equivalent resistance in thermal equilibrium which would give the same noise. Comparison of this set of values with the real part of the junction impedance in each case indicates that the theory advanced is adequate to predict noise under these circumstances. The signal-to-noise ratio for a photo-diode used as an open-circuit radiation detector is developed, and several recommendations are made regarding the design of a photo-diode to display the most favourable signal-to-noise ratio under illumination.

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