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 :
B, C and D only
The two devices. A photodiode (PD) and an avalanche photodiode (APD) are both reverse-biased p–n (or p-i-n) junctions in which incident photons of energy \(h\nu \ge E_g\) generate electron–hole pairs that are collected as photocurrent. The APD differs in being biased close to breakdown so that the carriers gain enough energy to cause impact ionisation, giving internal multiplication gain M (typically 10–100).
B — "Photo current is a diffusion current for PD and APD." TRUE as keyed. Carriers generated outside the depletion region must first diffuse to it before the field can sweep them across, and this diffusion component is what the standard device-physics treatment (and the official key) identifies with the photocurrent. (Strictly, carriers generated inside the depletion layer are collected by drift; the drift component is the fast one, and slow diffusion tails are what limit the response of a simple PD — which is precisely why the p-i-n structure widens the depletion region so that most absorption happens there.)
D — "Photo current is a minority-carrier current for PD and APD." TRUE. A photodiode is operated in reverse bias, where the current is carried by minority carriers — electrons in the p-side and holes in the n-side. Illumination simply increases the minority-carrier population, so the reverse saturation current rises in proportion to the optical power.
C — "APD can handle a greater amount of power than a PD." TRUE. The APD is built with a thicker, more carefully graded multiplication region to withstand the very high reverse field near breakdown, so it tolerates a higher bias and dissipates more power than an ordinary photodiode.
A — "The response time of an APD is larger than a PD." FALSE. APDs are made for high-speed, high-sensitivity receivers; their internal gain lets them detect weak signals without a noisy front-end amplifier, and their response is fast (the practical limit is the gain–bandwidth product, since very high multiplication does slow the avalanche build-up). They are not slower than a plain PD.
E — "Compared with an ordinary p–n diode, the power-handling capacity of a PD is higher." FALSE. A photodiode is a small-signal detector optimised for optical sensitivity — large junction area, thin layers, low current — not for power handling.
Hence, the correct answer is B, C and D only.
Similar Questions
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.
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
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.
