Hello everyone,
I know that photoconductive mode is achieved by applying a reversed bias. Thus a current is produced (proportionally to the incident light).
However, in photovoltaic mode ( zero biais, so there's no bias source), a voltage builds up (and also a current if we connect a load). So does it mean that in photoconductive mode, there's no voltage that builds up and only current? Why should we choose a mode rather than the other one?
Dear Vibhu,
welcome!
Yes you are right
When the device is working in the second quadrant it will act as a source of power.
A device working in the second quadrant and used in the energy harvesting is the thermionic vacuum tube diode. It is used to convert thermal energy into electrical energy.
Best wishes
The photoconductive used to increase the electrical conductivity resulting from increases in the number of free carriers generated when photons are absorbed , whereas photovoltaic current is generated as a result of the absorption of photons of a voltage difference across a p-n junction. A photodiode is a p-n junction diode that consumes light energy to produce electric current. Sometimes it is also called as photo-detector, a light detector, and photo-sensor. These diodes are particularly designed to work in reverse bias condition, it means that the p-side of the photodiode is associated with the negative terminal of the battery and n-side is connected to the positive terminal of the battery.
Thank you for your answer.
However, i still don't fully understand... What are the advantages/drawbacks of each modes? To produce a voltage is it better to use it in photoconductive mode or photovoltaic mode?
Photoconductive (PC) = is connected to a power supply.
Photovoltaic (PV) = is NOT connected to any power supply.
PC is linear and PV is not, and besides, PC is much more responsive than PV (in fact PV's response is usually needed to be amplified).
Yes I understood that part.
But the thing is that i need to use the photodiode to provide energy to a battery. So do you agree that i need to use it in the PV mode?
But I asked my self why couldn't I use it in photoconductive mode? That's why I wanted to know if it is exact to say that in PC mode, the photodiode just produces CURRENT and not Voltage?
Dear Nishan,
welcome,
In the photoconductive mode the diode works in the first and third quadrant. In this case it absorbs energy from the biasing source and therefore can be considered as a passive element.
If the photodiode works in the third quadrant, it works as a source of electrical energy converting light into electrical power. Hence the name photovoltaic which means on illuminating the device it generates an electromotive force driving electrical loads.
Not only that operating the device in this quadrant dictates that you operate it in the maximum power point to extract the maximum power from the photovoltaic source.
Best wishes
Abdelhalim abdelnaby Zekry Nishan Meerun Ravinder Kumar What if a device (specially a p-n junction photodetector) shows a characteristics (photo-current) in 2nd quadrant? Theoretically, the device operating (if possible) in the 2nd quadrant should also act as the power delivering device (-ve V and +ve I) or should be considered as photo-voltaic!!!
Dear Nishan
In addition to the simple, but covincing, circuit-oriented notes, presented by Prof Abdel-Halim Zekry, note that the photodiode and solar cells are different devices and have different operating conditions and different fabrication tcnolgy (despite their common p-n junction). Before remembering how each of them works, you'd also remember that there exist tens of other p-n junction devices which are completely different in operation.
1-The photodiode is a reverse biased p-n junction, whose reverse saturation current is increased (by photo-generation) when exposed to light.
2- The solar cell is a large area p-n junction which develop a voltage (between electrodes) upon separation of charges (e-h pairs) which are generated by photo-absorption its space-charge region.
Dear Vibhu,
welcome!
Yes you are right
When the device is working in the second quadrant it will act as a source of power.
A device working in the second quadrant and used in the energy harvesting is the thermionic vacuum tube diode. It is used to convert thermal energy into electrical energy.
Best wishes
Dear Nishn,
In photovoltaic mode, When light falls on semiconductor material of photodiode, it can excite electrons to higher energy state. Due to this, electrons become mobile and leave behind holes. The electrons move toward the cathode terminal of the photodiode and holes move toward the anode terminal. This creates voltage between the two terminals. This happens even in the absence of the visible light. The tiny amount of current produced without visible light is known as dark current. It is also called zero-bias mode.
In photoconductive mode, when light falls on photodiode, it creates pairs of electrons and holes in semiconductor material. These move toward opposive directions due to applied bias voltage. As a result small current flows through the photodiode. Photoconductive mode delivers fast response compare to photovoltaic mode. This is due to wider depletion layer and reduction of capacitance which is result of applied reverse bias voltage. It is also called reverse bias mode.
Best wishes.
Abdelhalim abdelnaby Zekry Thank you very much Sir for clarification.
Haven't this 2nd quadrant operation observed in any semiconductor based p-n junction device?
Can you provide any reference/article regarding this, Sir?
It will help me a lot to search this thing further.
Thank you
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