## Friday, 20 September 2013

### Previous GATE Questions on Extrinsic Semiconductors - Mass Action Law (1987 - 2013)

1.      In a P – Type silicon sample, the hole concentration is 2.25 x 1015 /cm3. If the intrinsic carrier concentration is 1.5 x 1010 /cm3, the electron concentration is                                 [GATE’95]

a.       Zero
b.      1010 /cm3
c.       105 /cm3
d.      1.5 x 1010 /cm3

2.       The intrinsic carrier density at 300oK is 1.5 x 1010 /cm3 for silicon. For N –Type silicon doped to 2.25 x 1015 /cm3, the equilibrium electron and hole densities are                         [GATE’97]

a.       N= 1.5 x 1015 /cm3 , P = 1.5 x 1010 /cm3
b.      N= 1.5 x 1010 /cm3 , P = 2.25 x 1015 /cm3
c.       N= 2.25 x 1015 /cm3 , P = 1.0 x 105 /cm3
d.      N= 1.5 x 1010 /cm3 , P = 1.5 x 1010 /cm3

3.       The electron and hole concentrations in a intrinsic semiconductor are ni and pi respectively. When doped with a P – Type material, these change to n and p, respectively. Then    [GATE’98]

a.       n + p = ni + pi
b.      n + ni  =  p + pi
c.       npi = nip
d.      np = nipi

4.       The intrinsic concentration of silicon sample of 300oK is 1.5 x 1016 /m3, if after doping, the number of majority carriers is 5 x 1020 /m3, the minority carrier density is       [GATE’03]
a.       4.50 x 1011 /m3
b.      3.33 x 104 /m3
c.       5.00 x 1020  /m3
d.      3.00 x 10-5  /m3

5.       The concentration of minority carriers in an extrinsic semiconductor under equilibrium is
[GATE’06]

a.       Directly proportional to the doping concentration
b.      Inversely proportional to the doping concentration
c.       Directly proportional to the intrinsic concentration
d.      Inversely proportional to the intrinsic concentration

6.       The electron and hole concentrations in an intrinsic semiconductor are ni per cm3 at 300oK. Now, if acceptor impurities are introduced with a concentration of NA per cm3 (where NA >  ni), then electron concentration per cm3 at 300oK will be                                  [GATE’07]

a.       ni
b.      ni + NA
c.       NA – ni
d.      ni2 / NA

7.       A silicon sample is uniformly doped with 1016 phosphorous  atoms / cm3 and 2x 1016 boron atoms/cm3 . if all the dopants are fully ionized, the material is                               [GATE’91]

a.        n-type with carrier concentration of 1016 /cm3
b.     p-type with carrier concentration of 1016 /cm3
c.     p-type with carrier concentration of 2x 1016 /cm3
d.    n-type with carrier concentration of 2x1016 /cm3