Que.21 A Si sample is doped with an In a homogeneously doped n-type semiconductor bar, holes are injected at one end of the bar. How will the holes flow to the other end? fixed number of group V impurities. The electron density n is measured from 4 K to 1200 K for the sample. Which one of the following is correct?
- (a) n remains constant over the temperature range
- (b) n increases monotonically with increasing temperature
- (c) n increases first, remains constant over a range and again increases with increasing temperature
- (d) n increases show a peak and then decreases with rising in temperature
Que.22 In a homogeneously doped n-type semiconductor bar, holes are injected at one end of the bar. How will the holes flow to the other end?
- (a) By drift mechanism only
- (b) By diffusion mechanism only
- (c) By a combination of drift and diffusion mechanisms
- (d) By recombination mechanism
Que.23 The drift velocity of electrons in silicon varies with applied electric field in which one of the ways?
- (a) It monotonically increases with increasing field
- (b) It first increases linearly, then sub-linearly increases and finally attains saturation with increasing field
- (c) It first increases, then decreases showing a negative differential region, again increases and finally saturates
- (d) The drift velocity remains unchanged with an increase in field
Que.24 Why does the mobility of electrons in a semiconductor decrease with increasing donor density?
- (a) Doping increases the effective mass of electrons
- (b) Doping decreases the relaxation time of electrons
- (c) Electrons are trapped by the donors
- (d) More holes are generated so that the effective mobility decreases
Que.25 The electron and hole concentrations, n and p respectively obey the relation np = ni2 where ni is the intrinsic carrier density. This expression is valid for which of the following?
- (a) For all semiconductors under any condition
- (b) For direct band gap semiconductors only
- (c) For non-degenerate semiconductors under thermal equilibrium condition
- (d) For degenerate semiconductors having excess electrons and holes
Que.26 An intrinsic semiconductor is doped lightly with a p-type impurity. It is found that the conductivity actually decreases till a certain doping level is reached. Why does this occur?
- (a) The mobility of holes decreases
- (b) The mobility of both electrons and holes decrease
- (c) The hole density actually reduces
- (d) Effect of reduction in electron due to increase in holes compensates more than the effect of an increase in holes on conductivity
Que.27 The doping concentration on the n-side of a p-n junction diode is enhanced. Which one of the following will get affected?
- (a) Width of the depletion region on n-side
- (b) Width of the depletion region on p-side
- (c) Width of the depletion region on both sides
- (d) No change in width of depletion regions
Que.28 What is the chemical bonding in silicon
- (a) Metallic
- (b) lonic
- (c) Covalent
- (d) Van der Waals
Que.29 Which one of the following is a trivalent material?
- (a) Antimony
- (b) Phosphorus
- (c) Arsenic
- (d) Boron
Que.30 In a material, the Fermi-level is located between the centre of the forbidden band and the conduction band. Then what is that material?
- (a) A p-type semiconductor
- (b) An n-type semiconductor
- (c) An intrinsic semiconductor
- (d) An insulator