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, C_J, of an abrupt PN junction with constant doping on either side varies with reverse bias, V_R as         [GATE'95]          

a.       C_J ∞ V_R

b.      C_J ∞ V_R^-1

c.       C_J ∞ V_R ^-1/2

d.      C_J ∞ V_R ^-1/3

   4.       Consider an abrupt PN junction. Let V_bi be the built in potential of this junction and V_R be the applied reverse bias. If the junction capacitance (C_j) is 1 pF for V_bi + V_R = 1 volt, then for V_bi + V_R = 4 volts, C_j 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 Ɛ_r is 11.7 and the permittivity of free space Ɛ_o = 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