I am working on two types of MSM photodetector ,on of them ohmic the other one schottcky. I studied sensitivity of both detectors, I saw sensitivity decreasing at high voltage in range (5-10)v
The question is why did sensitivity decrease at high voltage(5-10)v of MSM photodetector?
sensitivity =photocurrent/dark current
Dear Sha,
I agree with Han interpretation. However let make some comments which may be useful for this issue:
- The sensitivity of the photo detector is normally defined by the ratio of the photocurrent to the the power of the incident radiation.
- From the shape of the dark characteristics one can identify the the type of the MS contact, i. e. , whether it is rectifying or ohmic. If it is rectifying then it operates as a photdiode. When it is ohmic it will act as a photocoductor or a photoresistor.
- Photodiodes working in reverse bias have their photocurrent constant with the reverse voltage so long as they do not enter in breakdown region. Their dark current is equal to the reverse saturation current which may increase with the reverse voltage.
- In case of a photoconductor The photocurrent may increase linearly with the applied voltage while the dark current may increase at low voltage linearly and then more than linear at higher voltage because of the heating effects as hinted by Han. So the ratio will be constant at low voltage where the heating effect is negligible and the decreases at high voltage because of the heating effect.
You can prove that by measuring the currents as a function of the voltage.
wish you success.
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Dear sha ..... how are you ? how Dr.YOUSIF my regards to all of you
regarding to your question , you have to get some information about the filed that created when u increase the voltage , we have three regions Flat‐Band Voltage, Threshold Voltage, then u can understand why when increase voltage decrease sensitivity .
Maybe the dark current increases with the applied voltage. Since Schottky barrier thickness reduce and this causes appreciable tunneling current.
Dear Naser
thank you for your help .I understand very well that there are three regions calculated by this equation: I~V M m shows how current transports in semiconductor
these things above is for schottky msm.what do you think about sensitivity of ohmic msm.
I think that the ohmic contact MSM should be called as photo-resistor. High voltage operation causes self-heating problem. In this case, both thermal-generated carriers and photo-generated carriers are collected by the electrodes. Therefore, the photo-to-dark current ratio is limited.
Dear Han
thanks for your help.i compared between two msm photo detecters schottky and ohmic in the same design because of that i call it ohmic msm.i appreciate your answer...
Dear Sha,
I agree with Han interpretation. However let make some comments which may be useful for this issue:
- The sensitivity of the photo detector is normally defined by the ratio of the photocurrent to the the power of the incident radiation.
- From the shape of the dark characteristics one can identify the the type of the MS contact, i. e. , whether it is rectifying or ohmic. If it is rectifying then it operates as a photdiode. When it is ohmic it will act as a photocoductor or a photoresistor.
- Photodiodes working in reverse bias have their photocurrent constant with the reverse voltage so long as they do not enter in breakdown region. Their dark current is equal to the reverse saturation current which may increase with the reverse voltage.
- In case of a photoconductor The photocurrent may increase linearly with the applied voltage while the dark current may increase at low voltage linearly and then more than linear at higher voltage because of the heating effects as hinted by Han. So the ratio will be constant at low voltage where the heating effect is negligible and the decreases at high voltage because of the heating effect.
You can prove that by measuring the currents as a function of the voltage.
wish you success.
-
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