28. Which of the following statements are correct ?
1. In semiconductor, the mobility of electrons is more than that of holes.
2. In semiconductor, when temperature increases, the resistivity also increases.
3. Metal has positive TCR.
4. In metals, thermal conductivity is inversely proportional to electrical conductivity at constant temperature.
(a) 1, 2, 3
(b) 1, 2, 4
(c) 2, 3, 4
(d) 1, 3, 4
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- Semiconductor Materials » Exercise - 4 151. The addition of a very small quantity of aluminium to a silicon or germanium crystal makes it : (a) A good conductor (b) A good insulator (c) P-type semiconductor (d) N-type semiconductor 152. An intrinsic semiconductor at the absolute zero of temperature : (a) Behaves like a semiconductor (b) Behaves like an insulator (c) Has a few free electrons and same number of holes (d) Has a large number of holes and a few electrons 153. In a substance the conduction band and valence band are separated by a energy gap of the order of 1 eV, and there are at room temperature as money electrons in the conduction band as holes in the valence band. The substance is : (a) An intrinsic semiconductor (b) A p-type semiconductor (c) A N-type semiconductor (d) A doped semiconductor 154. The majority carriers of electricity in a p-type semiconductor are : (a) Free electrons (b) Holes (c) Both electrons and holes (d) Free ions 155. N-type semiconductor is obtained when silicon or germanium is doped by : (a) Phosphorus (b) Boron (c) Aluminium (d) Gallium 156. A p-type semiconductor is : 1. A silicon crystal doped with arsenic impurity. 2. A silicon crystal…