## Saturday, 21 September 2013

### Previous GATE Questions on Diode Capacitances (Diffusion and Transition Capacitance)

1.       In a junction diode  [GATE'90]

a.       The depletion capacitance increases with increase in the reverse bias
b.      The depletion capacitance increases with decrease  in the reverse bias
c.       The diffusion capacitance increases with increase in the forward bias
d.      The diffusion capacitance is much higher than the depletion capacitance, when its is forward biased

2.       The small signal capacitance of an abrupt P+N junction is 1 nF/cm2 at zero bias. If the built in voltage is 1  volt, the capacitance at a reverse bias voltage of 99 volts is equal to …..    [GATE’91]

3.       The depletion capacitance, CJ, of an abrupt PN junction with constant doping on either side varies with reverse bias, VR as         [GATE'95]

a.       CJ VR
b.      CJ ∞ VR-1
c.       CJ ∞ VR -1/2
d.      CJ ∞ VR -1/3

4.       Consider an abrupt PN junction. Let Vbi be the built in potential of this junction and VR be the applied reverse bias. If the junction capacitance (Cj) is 1 pF for Vbi + VR = 1 volt, then for Vbi + VR = 4 volts, Cj will be                                                                                                                                       [GATE’04]

a.       4 pF
b.      2 pF
c.       0.25 pF
d.      0.5 pF

5.       A silicon PN junction diode under reverse bias has depletion region of width 10µm. the relative permittivity of silicon Ɛr is 11.7 and the permittivity of free space Ɛo = 8.85x10-12 F/m. the depletion capacitance of the diode per square meter is       [GATE’05]
a.       100 µF
b.      10 µF
c.       1 µF
d.      20 µF

6.       Which of the following is NOT associated with a P-N junction ?      [GATE'08]

(A)   Junction capacitance                                      (B) Charge Storage Capacitance
(C) Depletion Capacitance                                   (D) Channel Length Modulation

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