Photovoltaic detectors photocurrent

Estimate the maximum output voltage of an open photovoltaic detector at room temperature under 10)jiW irradiation when the photocurrent of the shortened output is 50 p.A and the dark current is 50 nA. 

Photovoltaic detector (detector with p-n junction, PV detector, photovoltaic) Photoexcitation creates an electron-hole pair to be separated at the p-n junction, thus generating photocurrent. In dependence on the structure type and the junction used it may belong to a number of the existing types with homojunction or heterojunction, p-i-n photodiode. Camel s diode (photodiode with modulated barrier), avalanche photodiode (APD), bipolar phototransistor (floating-base), etc. 

Materials used for photovoltaic detectors are, e.g., silicon, cadmium sulfide (Cds), and gallum arsenide (GaAs). Si detectors deliver photovoltages up to 550 mV and photocurrents up to 40 mA/cm [4.82], The efficiency rj = Pgi/Pph of energy conversion reaches 10fl4%. GaAs detectors... 

The absolute sensitivity 5(A) = V /P, which is defined as the ratio of output signal Vs to incident radiation power F. If the output is a voltage, as in photovoltaic devices or in thermocouples, the sensitivity is expressed in units of volts per watt. In the case of photocurrent devices, such as photomultipliers, 5(A) is given in amperes per watt. With the detector area A the sensitivity 5 can be expressed in terms of the irradiance I ... 

Optimum Bias for PhotovoUaics To select the optimum bias for photovoltaic (PV) detectors, we could use the method described for PC detectors - but a simpler method is available. Unlike the PC detectors the photocurrent and respon-sivity of PV deteetors are only slightly bias dependent in their usual bias range. To determine the optimum bias, we need only look for the minimum noise in a plot of noise versus bias. It is a good idea to also plot the DC output versus bias so we know where in the /-Vplot we are trying to operate. Figure 10.6 illustrates this. 

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