Assertion (A) : In PIN photodiodes, an intrinsic layer is there, which is slightly doped with n type material. Reason (R) : It disables us to increase the width of the depletion region to a value which is far lesser what it could be in a PN diode. Select your answer using the codes given below.
(A) is true, but (R) is false
Examine the assertion — true. The "i" layer of a PIN photodiode is not perfectly intrinsic in practice. It is a very lightly doped region — usually slightly n-type, written ν (nu), or occasionally slightly p-type, written π (pi) — because material of truly zero net doping cannot be grown. It is called intrinsic because its doping is negligible compared with the heavily doped p+ and n+ regions on either side, not because it contains no impurities at all.
Examine the reason — false, and it is doubly so. As written it claims the intrinsic layer "disables us to increase the width of the depletion region", and that it becomes "far lesser" than in a PN diode. Both halves invert the truth.
Because the middle layer is almost undoped it contains very little charge to terminate the field, so the depletion region sweeps straight through it. The layer thickness therefore sets the depletion width directly:
\(W\approx W_i\)
and Wi is a design choice, typically 20–50 μm against a fraction of a micrometre in an ordinary p-n junction. So the intrinsic layer enables a depletion region far wider, not narrower.
Assemble. (A) is true and (R) is false, which is code 3.
Why the wide depletion region is the entire point. Three benefits follow at once, and they are why the PIN structure exists.
| Consequence | Reason |
|---|---|
| High quantum efficiency | Nearly all photons are absorbed inside the depletion region, where the field separates the pair before it can recombine |
| Low junction capacitance | \(C_j=\dfrac{\epsilon A}{W}\) — a wide W means small C, so the RC time constant falls and the bandwidth rises |
| Fast, drift-dominated response | Carriers generated in the field drift at saturation velocity instead of diffusing slowly |
The one trade-off. Widening W lowers the capacitance but lengthens the transit time \(t_{tr}=W/v_s\), so there is an optimum thickness for any given speed target — roughly where transit time and RC time are comparable.
The material choice that goes with it. Silicon PIN diodes serve 0.8–0.9 μm; the 1.3 and 1.55 μm fibre windows need InGaAs, whose narrower gap absorbs at those wavelengths.
Hence, (A) is true, but (R) is false.
Similar Questions
Consider the following statements for photo diode (PD) and Avalanche Photo Diode (APD)
A. The response time of APD is larger than PD
B. Photo current is a diffusion current for PD and APD
C. APD can handle greater amount of power in comparison to PD
D. Photo current is a minority carrier current for PD and APD
E. compare to ordinary pn diode, power handling capacity of PD is higher.
Choose the correct answer from the options given below :
In a p-i-n photodiode the depletion region thickness can be tailored to
(a) optimize the quantum efficiency
(b) optimize the frequency response
(c) optimize the quantum efficiency but not the frequency response.
(d) optimize the frequency response but not the quantum efficiency.
Out of these
In case a reverse biased photodiode is kept in dark condition, the current flowing through the device corresponds to:
Given below are two statements :
Statement I : In case a reverse biased photodiode is kept in a open light, the current flowing through the device corresponds to value of reverse saturation current.
Statement II : Photovoltaic emf of semiconductor photodiode is that voltage at which the resultant current flowing the device becomes zero.
In the light of the above statement, choose the most appropriate answer from the options given below :
Assertion (A) : Those semiconductor materials that have practically no thermally generated current carriers at room temperature are used as photoconductors.
Reason (R) : These materials are essentially insulators in the dark and carriers generated by the absorption of light cause maximum possible change in the resistivity of the cell.
Select your answer using the codes given below.
Photodiode can be used as :
(a) as a detector in forward biased
(b) as a detector in reverse biased
(c) as an LDR
(d) it generates solar energy
Which of the above statements are correct ?
The carrier velocity in a silicon p-i-n photodiode with 25 μm depletion layer width is 3 × 104 m/s. The maximum response time for the pin diode is given by :
Consider the following statements :
(A) The charge coupled device (CCD) is a linear scanning system
(B) The charge coupled device is a non linear scanning system
(C) A charge coupled devices is used as a shift register
(D) A charge coupled device can not be used as a photo detectorChoose the most appropriate answer from the options given below :
Important Questions from Photodetectors - Teaching
Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: In a photodetector, it is desired that the width of the depletion region W be large enough so that most of the photons are absorbed within W rather than in the neutral n and p regions.
Reason R: A wider width W results in small junction capacitance.
In the light of the above statements, choose the most appropriate answer from the options given below
Consider the following statements for photo diode (PD) and Avalanche Photo Diode (APD)
A. The response time of APD is larger than PD
B. Photo current is a diffusion current for PD and APD
C. APD can handle greater amount of power in comparison to PD
D. Photo current is a minority carrier current for PD and APD
E. compare to ordinary pn diode, power handling capacity of PD is higher.
Choose the correct answer from the options given below :
In a p-i-n photodiode the depletion region thickness can be tailored to
(a) optimize the quantum efficiency
(b) optimize the frequency response
(c) optimize the quantum efficiency but not the frequency response.
(d) optimize the frequency response but not the quantum efficiency.
Out of these
In case a reverse biased photodiode is kept in dark condition, the current flowing through the device corresponds to:
Given below are two statements :
Statement I : In case a reverse biased photodiode is kept in a open light, the current flowing through the device corresponds to value of reverse saturation current.
Statement II : Photovoltaic emf of semiconductor photodiode is that voltage at which the resultant current flowing the device becomes zero.
In the light of the above statement, choose the most appropriate answer from the options given below :
