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 300^oK 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 n_i and p_i respectively. When doped with a P – Type material, these change to n and p, respectively. Then    [GATE’98]

a.       n + p = n_i + p_i

b.      n + n_i  =  p + p_i

c.       np_i = n_ip

d.      np = n_ip_i

   4.       The intrinsic concentration of silicon sample of 300^oK 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 n_i per cm³ at 300^oK. Now, if acceptor impurities are introduced with a concentration of N_A per cm3 (where N_A >  n_i), then electron concentration per cm³ at 300^oK will be                                  [GATE’07]

a.       n_i

b.      n_i + N_A

c.       N_A – n_i

d.      n_i² / N_A

   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