Question:

Pure Si at 500 K has equal number of electron (ne) and hole (nh) concentration of 1.5 × 1016 m-3. Doping by indium increases nh to 4.5 × 1022 m-3. The doped semiconductor is of

n-type with electron concentration ne = 5 × 1022 m-3

n-type with electron concentration ne = 2.5 × 1023 m-3

p-type with electron concentration ne = 2.5 × 1010 m-3

p-type having electron concentration ne = 5 × 109 m-3

The correct option is D (p-type having electron concentration ne = 5 × 109 m-3)

ni2 = nenh
(1.5 × 1016)2 = ne(4.5 × 1022)
ne = 0.5 × 1010
ne = 5 × 109
nh = 4.5 × 1022
nh >> ne
Semiconductor is p-type and ne = 5 × 109 m-3.