If I take just a PIN photodiode (e.g. BPW34 FAS ) and connect a multimeter to its terminals to measure current, for example: expose the photodiode to the sunlight and read current of ~1 mA on the multimeter. In what region do I operate the photodiode with respect to bias voltage, that is do I have zero, forward or reverse bias voltage ? What is the bias voltage (or how it can be found) if not zero ?
expose the photodiode to the sunlight and read current of ~1 mA on the multimeter.
I will assume this means you're using the multimeter in ammeter mode.
In what region do I operate the photodiode with respect to bias voltage, that is do I have zero, forward or reverse bias voltage ?
The meter should not be applying any bias in ammeter mode.
It will have a small "burden resistance", meaning as the photodiode starts top push current through the meter, the voltage across the meter will increase slightly.
The result is you are essentially using the photodiode in photovoltaic mode, but with a very low load resistance (which isn't how we typically use photovoltaic mode).
What is the bias voltage (or how it can be found) if not zero ?
You could put a second meter across the photodiode and put it in voltmeter mode.
You were operating in PV mode with an internal shunt R to measure almost short cct. current. assuming 1mA in current mode on DMM.
Photovoltaic (PV) - -- - - Photoconductive (PC)
Solar cell mode Zero bias applied Reverse biased No "dark" current Has "dark" current Linear Nonlinear Low noise (i.e. Johnson) Higher noise (i.e. Johnson, Shot) max. junction capacitance low capacitance reduces with higher Vr Used in precision applications Used in high-speed applications
BPW 34 FAS Datasheet:
- Isc = 23 µA typ. - Voc = 250 mV min. 320 mV typ. - 72 pF @ 0V - 0.65 mA / mW @ λ = 870 nm - Radiant sensitive area A = 7.02 mm² typ.
Sunlight ≈ 1 kW/m² = 100mW/mm²