Saturday, 21 September 2013

Previous GATE Questions on Diode (PN Junction) - 1


Previous GATE Questions on Diode - 1 includes Diode under open circuit, built in potential barrier, electric field, width of potential barrier etc.....



   1.       In a uniformly doped abrupt PN junction, the doping level of the N-side is four times the doping level of the P-side. The ratio of the depletion layer widths is                                                              [G’90]

a.       0.25
b.       0.50              
c.        1.0                
d.       2.0


   2.       The built in potential (Diffusion Potential) in a PN junction                                                         [G’93]

a.       Is equal to the difference in the Fermi level of the two sides, expressed in volts.
b.      Increases with the increase in the doping levels of the two sides
c.       Increases with the increase in temperature
d.      Is equal to the average of the Fermi levels of the two sides



   3.       In a P+N junction diode under reverse bias, the magnitude of electric field is maximum at   [G’07]    
        
a.       The edge of the depletion region on the p side
b.       The edge of the depletion region on the n-side
c.       The P+N junction
d.      The centre of the depletion region on the n-side


   4.       Consider a silicon P-N junction at room temperature having the following parameters :  [G’09]
Doping on the n-side = 1 x 1017 cm-3
Depletion width on the n-side = 0.1 um
Depletion width on the p-side = 1.0 um
Intrinsic carrier concentration = 1.4 x 1010 cm-3
Thermal voltage = 26 mV
Permittivity of free space = 8.85 x 10-14 F.cm-1
Dielectric constant of silicon = 12

The built in potential of the junction is   

  (A)   0.70 V                    (B) 0.76 V              (C) 0.82 V            (D) cannot be estimated from the given data

The peak electric field in the device is

  (A)   0.15 MV . cm-1, directed from p-region to n-region
  (B)   0.15 MV . cm-1, directed from n-region to p-region
  (C)   1.80 MV . cm-1, directed from p-region to n-region
  (D)   1.80 MV . cm-1, directed from n-region to p-region


   5.       In a Forward Biased PN junction diode, the sequence of events that best

 describes the mechanism of current flow is                                                                                        [G’13]

a.       Injection and subsequent diffusion and recombination of minority carriers
b.      Injection and subsequent drift and generation of minority carriers
c.       Extraction and subsequent diffusion and generation of minority carriers
d.      Extraction and subsequent drift and recombination of minority carriers 


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