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
(a) and (b) are correct
Why the intrinsic layer exists. Inserting a lightly doped i region between the p and n layers puts a wide, fully depleted, high-field region exactly where the light is absorbed. Its thickness W is a design variable, and it controls two competing figures of merit — which is the whole point of the question.
(a) Quantum efficiency ✓. The fraction of incident photons that produce collected carriers is
\(\eta=(1-R)\left(1-e^{-\alpha W}\right)\)
so a thicker depletion region absorbs more of the light and raises η. The layer must be several absorption lengths deep, and because α falls at longer wavelengths, detectors for 1550 nm need thicker i-regions than those for 850 nm.
(b) Frequency response ✓. The speed is limited by the time carriers take to drift across that same region:
\(t_{tr}=\dfrac{W}{v_{sat}}, \qquad f_{3dB}\approx\dfrac{0.45}{t_{tr}}\)
so a thinner region is faster. A wider region also reduces the junction capacitance \(C_j=\varepsilon A/W\), which helps the RC limit — so the two speed mechanisms pull in opposite directions and there is an optimum.
Both can be tailored, so (a) and (b) are correct — option 1. Statements (c) and (d) each deny one of them, and both denials are false.
The trade-off in one line. Thick W → high efficiency but slow; thin W → fast but insensitive. The designer chooses W to balance the transit-time and RC limits for the wavelength and bit rate in hand — and that freedom is precisely why the p-i-n structure replaced the simple p-n photodiode, where the depletion width is fixed by the doping and the bias.
Hence, the correct answer is (a) and (b).
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 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.
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.
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 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.
