### GATE Questions on "Special Purpose Diodes (Tunnel diode, LED, PIN diode, Photo diode & LASER)" (1987 to Till Date)

1990

1. In a forward biased photo diode, with increase in incident light intensity, the diode current
a.  increasees
b.  remains constant
c.  decreases
d.  remains constant, but the voltage drop across the diode increases.
Solution :

2. SCR can be turned On by
a. Applying anode voltage at sufficiently fast rate
b. Applying sufficiently large anode voltage
c. Increasing the temperature of SCR to a sufficiently large value
d. Applying sufficiently large gate current

Answer:  All are correct, most accurate is D

1992

1.       An infrared LED is usually fabricated from
a.       Ge
b.      Si
c.       GaAs
d.      GaAsP

2003

1.       Choose proper substitutes for X and Y to make the following statement correct.
Tunnel diode and Avalanche photo diode are operated in X bias and Y bias respectively.

2.       Match items in Group 1 with items in Group 2, most suitably,

3.   A particular green LED emits light of wavelength 5490 Ao. The energy band gap of the semiconductor material used there is (Plank’s constant = 6.626 x 1034 J-Sec)
a.       2.26 eV
b.      1.98 eV
c.       1.17 eV
d.      0.74 eV

2004

1.   The longest wavelength that can be absorbed by silicon, which has the band gap of 1.12 eV is 1.1 µm. If the longest wavelength that can be absorbed by another material is 0.87 µm, then the band gap of this material is
a.       1.416 eV
b.      0.886 eV
c.       0.854 eV
d.      0.706 eV

2006

1.       The values of voltage across a tunnel diode (VD) corresponding to peak and valley currents are VP and VV respectively. The range of tunnel diode voltage VD for which the slope of its I-V characteristics is negative would be

2.       Find the correct match between Group 1 and Group 2 :

2007

1.       Group I lists four types of PN junction diodes. Match each device in Group I with one of the option in Group II to indicate the bias condition of that device in its normal mode of operation.

2.       Group I lists four different semiconductor devices. Match each device in Group I with its characteristic property in Group II.

2014
Set – 1 (15th February 2014 (Forenoon))

1.       When the optical power incident on a photo diode is 10 µW and the responsivity is 0.8 A/W, the photo current generated (in µA) is ____________.

2.       In the figure, assume that the forward voltage drops to the PN diode D1 and Schottky diode D2 are 0.7 volts and 0.3 volts respectively. If ON denotes conducting state of the diode and OFF denotes the non conducting state of the diode, then in the circuit,

a.       Both are ON
b.      D1 is ON and D2 is OFF
c.       Both are OFF
d.      D1 is OFF and D2 is ON

SET  - 4  (16th February 2014 (Afternoon))

1.       At T = 300oK, the band gap and the intrinsic carrier concentration of GaAs are 1.42 eV and 106 cm-3 respectively. In order to generate electron hole pairs in GaAs, which one of the wavelength (λc) ranges of incident radiation, is most suitable? (Given that Plank’s constant = 6.62 x 10-34 J-sec, velocity of light is 3 x 1010 cm/s and charge of electron is 1.6 x 10-19C)
a.       0.42 µm < λc < 0.87 µm
b.      0.87 µm < λc < 1.42 µm
c.       1.42 µm < λc < 1.62 µm
d.      1.62 µm < λc < 6.62 µm

2.       The cutoff wavelength (in µm) of light that can be used for intrinsic excitation of a semiconductor material of band gap Eg = 1.1 eV is …………..

2015

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