Friday, 20 September 2013

Previous GATE Questions on Drift, Diffusion and Hall Effect

     1.     A small concentration of minority carriers is injected into a homogeneous semiconductor crystal at one point. An electric field of 10 V/cm is applied across the crystal and this moves the minority carriers a distance of 1 cm in 20 µsec. the mobility in cm2/volt-sec will be               [GATE’94]
a.       1,000
b.      2,000
c.       5,000
d.      50,000

    2.       [GATE’10]


    3.       Drift current in semiconductors depends upon                  [GATE’11]
a.       Only the electric field
b.      Only the carrier concentration gradient
c.       Both the electric field and the carrier concentration
d.      Both the electric field and the carrier concentration gradient

    4.       The electron concentration in a sample of uniformly doped n-type silicon at 300oK varies linearly from 1017 /cm3 at x = 0 µm to 6 x 1016 /cm3 at x = 2 µm. Assume a situation that electrons are supplied to keep this concentration gradient constant with time. If electronic charge is 1.6 x 10-19 coulomb and the diffusion constant Dn = 35 cm2/sec, the current density in the silicon, if no electric field is present, is                                                                                                [GATE’03]
a.       Zero
b.      -112 A/cm2 
c.       +1120 A/cm2 
d.      -1120 A/cm2  

    5.       Under low level injection assumption, the injected minority carrier current for an extrinsic semiconductor is essentially the                                                                   [GATE’06]
a.       Diffusion current
b.      Drift current
c.       Recombination current
d.      Induced current

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