Question 1

Light-emitting diodes are semiconductors that emit light when a current is passed through them. What is the key factor that must be changed to change the wavelength of the emitted light in an LED?
A)the width of the valence band
B)the width of the conduction band
C)the width of the band gap
D)the magnitude of the current
E)the type of semiconductor (p vs.n)

Accepted Answer

The wavelength of the emitted light is determined by the width of the band gap in the semiconductor material. As the width of the band gap changes, the energy levels of the electrons in the valence and conduction bands also change, leading to a different wavelength of emitted light. Changing the width of the valence and conduction bands, the magnitude of the current, or the type of semiconductor would not have a direct effect on the wavelength of the emitted light.

Question 2

Band theory of bonding in solids ________
A)is an extension of molecular orbital theory.
B)describes bonds as rubber bands.
C)does not apply to any type of solid other than metals.
D)explains bond formation in metals, but not their physical properties.
E)All of the above are correct.

Accepted Answer

The band theory of bonding in solids is an extension of molecular orbital theory, which explains how atoms bond to form molecules. The band theory explains how atoms bond in solids, particularly in metals, by creating energy bands or levels of electrons.

Answer: E 
 The band theory of bonding in solids is an extension of molecular orbital theory. It does not describe bonds as rubber bands and applies to any type of solid, but is particularly useful for metals. The theory explains bond formation in metals and their physical properties by creating energy bands or levels of electrons.

Question 3

Which of the following elements are semiconductors? C, Si, Ge, Sn
A)C and Si only
B)Si and Ge only
C)Ge and Sn only
D)None of these elements are semiconductors unless a dopant is added.
E)All of these elements are semiconductors.

Accepted Answer

Semiconductors are materials that have electrical conductivity between conductors (metals) and insulators (nonmetals). Of the given elements, only Si and Ge are semiconductors. While C and Sn are not semiconductors unless they are doped with certain impurities.

Question 4

Which statement about a semiconductor is not correct?
A)Both electrons in the conduction band and holes in the valence band conduct electricity.
B)The band gap becomes smaller with increasing temperature.
C)The band gap is smaller than in an insulator.
D)Adding an impurity can increase the conductivity.
E)Conductivity increases with increasing temperature.

Accepted Answer

The statement "the band gap becomes smaller with increasing temperature" is not correct. In fact, the band gap generally increases with increasing temperature.

Question 5

Which element would be used to dope germanium to produce an n-type semiconductor?
A)Ga
B)Sn
C)Si
D)As
E)Cu

Accepted Answer

Doping is the process of intentionally introducing impurities into a pure semiconductor crystal in order to change its electrical properties. To produce an n-type semiconductor, impurities with excess electrons must be added to the pure semiconductor. Therefore, the best choice for doping germanium to produce an n-type semiconductor is an impurity that has one more valence electron than germanium, such as arsenic (As) which has five valence electrons. Therefore, the answer is D.

Question 6

Electrical and thermal conductivity in metals ________
A)is explained by a dipolar coupling model.
B)is explained by band theory.
C)is explained by matrix isolation techniques.
D)is explained by temporary ionization.
E)is a function of the level of contamination by excess electrons.

Accepted Answer

The band theory explains the electrical and thermal conductivity in metals. According to this theory, metals have a partially filled valence band, and a conduction band that is partially filled or completely empty. The electrons in the valence band contribute to the metallic bonding, while those in the conduction band are free to move and carry electrical and thermal energy.

Question 7

Molecular orbital theory can be applied ________
A)only to two adjacent metal atoms.
B)only to a few metal atoms that are very close to each other.
C)to any number of metal atoms.
D)to nonmetals only, not to metals.
E)to nonmetals and ionic bonds only, not to metals.

Accepted Answer

Molecular orbital theory can be applied to any number of metal atoms, not just a few or two adjacent ones. It is applicable to both metals and nonmetals.

Question 8

When Ge is doped with Ga, it produces a(n) ________-type semiconductor.
A)p
B)n
C)q
D)np
E)No semiconductor will be produced.

Accepted Answer

When Ge (Germanium) is doped with Ga (Gallium), it produces a p-type semiconductor. This is because Gallium has one less valence electron than Germanium, leading to the creation of "holes" that act as positive charge carriers.

Question 9

Which element would be used to dope silicon to produce a p-type semiconductor?
A)boron (B)
B)carbon (C)
C)aluminum (Al)
D)phosphorus (P)
E)germanium (Ge)

Accepted Answer

The answer of Which element would be used to dope...

Question 10

Which of the following materials could be classified as a p-type semiconductor?
A)Ge doped with As
B)C doped with P
C)Si doped with B
D)Sn doped with Sb
E)None of these are p-type semiconductors.

Accepted Answer

The presence of boron dopant in Si creates a hole in the valence band of silicon, making it a p-type semiconductor.

Question 11

Metal solids are good conductors of electricity because ________
A)they are easily ionized.
B)their valence electrons are not localized.
C)they are easily reduced and oxidized.
D)they can be drawn into wires.
E)they are ductile.

Accepted Answer

Metal solids have a unique structure where the valence electrons are delocalized and can move freely throughout the structure. This allows for easy transfer of electrons and makes them good conductors of electricity. Choices A, C, D, and E are all properties of metals but do not directly relate to their conductivity.

Question 12

The molecular orbital description for metal bonding is different from that for diatomic molecules in that ________
A)there are no antibonding orbitals in the metal bonding description.
B)quantum theory no longer applies as the orbitals are continuous.
C)the orbitals are so close in energy that they are referred to as bands.
D)the increased number of electrons results in each bond being stronger.
E)All of the above are true.

Accepted Answer

In the molecular orbital description for metal bonding, the orbitals are so close in energy that they overlap and form bands, rather than distinct molecular orbitals. This is due to the large number of electrons and the delocalized nature of the metal atoms. Therefore, option C is the correct answer. Option A is incorrect because there are antibonding orbitals in the metal bonding description, but they are generally higher in energy and do not play a significant role in bonding. Option B is incorrect because quantum theory still applies to metals, and the continuous nature of the orbitals is a consequence of the delocalization of the electrons. Option D is also incorrect because the increased number of electrons can lead to stronger bonding, but this is not a defining feature of metal bonding.

Question 13

The band structure of semiconductors differs from that of metal conductors in that ________
A)metal bands are relatively empty, while semiconductor bands are nearly full.
B)metal bands are nearly full, while semiconductor bands are relatively empty.
C)metal conduction bands are lower in energy than valence bands, while semiconductor conduction bands are higher in energy than valence bands.
D)metal conduction bands are higher in energy than valence bands, while semiconductor conduction bands are lower in energy than valence bands.
E)valence bands in metals are either partially empty or overlap with conduction bands, while these bands in semiconductors are separated by a small gap.

Accepted Answer

The band structure of semiconductors differs from that of metal conductors in that valence bands in metals are either partially empty or overlap with conduction bands, while these bands in semiconductors are separated by a small gap.

Question 14

GaAs and AlGaAs₂ are examples of ________ semiconductors. A)light-emitting diode (LED) B)sound-emitting C)np D)non- E)dual voltage

Accepted Answer

GaAs (Gallium Arsenide) and AlGaAs (Aluminum Gallium Arsenide) are materials commonly used in the manufacture of light-emitting diodes (LEDs) due to their direct bandgap properties, which allow for efficient light emission.

Question 15

When silicon is doped with gallium, electrical conduction increases because ________
A)gallium has fewer valence electrons than silicon, so holes are created in the valence band of silicon.
B)gallium has more valence electrons than silicon, so electrons are added to the conduction band of silicon.
C)gallium causes electrons to be transferred from the valence band of silicon to the conduction band of silicon.
D)gallium causes electrons to be transferred from the conduction band of silicon to the valence band of silicon.
E)gallium is a better conductor of electricity than silicon.

Accepted Answer

Gallium has one fewer valence electron than silicon, so when it is doped into silicon, it creates a hole in the valence band that can be easily filled by an electron from an adjacent atom. This increases electrical conductivity as the movement of electrons is more facilitated in the semiconductor.

Question 16

When Si is doped with P, it produces a(n) ________-type semiconductor.
A)p
B)n
C)q
D)np
E)No semiconductor will be produced.

Accepted Answer

When Si is doped with P, it produces an n-type semiconductor. This is because P has 5 valence electrons whereas Si has 4 valence electrons. When P is added to Si, it brings an extra electron, which creates an excess of negative charge carriers (electrons) in the crystal lattice, leading to the n-type semiconductor.

Question 17

Which statement regarding the electronic structure of solids is not correct?
A)The band theory of solids is like molecular orbital theory in that the electronic wave function is delocalized to some extent over all the constituent atoms.
B)In solids that are electrical insulators, there is a large gap between a filled valence band and a vacant conduction band.
C)In semiconductors, the gap between the valence band and conduction band is small, so a few electrons have sufficient thermal energy to be found in the conduction band.
D)N- and p-type semiconductors can be produced by doping a semimetal with an element from a different group.
E)Germanium doped with arsenic is a p-type semiconductor.

Accepted Answer

Germanium doped with arsenic is actually an n-type semiconductor, not a p-type. This is because arsenic has one extra electron than germanium, and when it is incorporated into the semiconductor lattice, it becomes a donor atom that provides an extra electron to the conduction band. In a p-type semiconductor, an acceptor atom is used to create a vacancy or “hole” in the valence band, which can be filled by electrons from neighboring atoms, creating a net positive charge.

Question 18

Which of the following materials could be classified as an n-type semiconductor?
A)C doped with Ga
B)Ge doped with Sn
C)Se doped with Sb
D)Si doped with As
E)None of these are n-type semiconductors.

Accepted Answer

N-type semiconductors are created by doping an intrinsic semiconductor with impurities that have extra valence electrons. As a result, in D, As (arsenic) has five valence electrons and substitutes into Si's (silicon) crystal structure, forming an extra electron for conductivity. A p-type semiconductor is formed by doping with an impurity that has one fewer valence electrons, as opposed to an n-type semiconductor.

Question 19

Which statement A-D regarding semiconductors is not correct?
A)An undoped semiconductor does not conduct electricity because it has a filled valence band and a vacant conduction band.
B)Doping silicon with phosphorous produces an n-type semiconductor.
C)An n-type semiconductor has electrons in its conduction band.
D)Doping silicon with gallium removes electrons from the valence band to enhance the conductivity.
E)Statements A-D all are correct.

Accepted Answer

All statements A-D correctly describe aspects of semiconductor physics. A) describes the intrinsic (undoped) semiconductor behavior, B) and C) explain n-type doping and its effect, and D) describes p-type doping by introducing holes in the valence band, which also enhances conductivity.

Question 20

Which of the following can be used to increase the conductivity of any semimetal?
I.adding an element with one additional valence electron
II.adding an element with one fewer valence electron
III.lowering the temperature
A)I only
B)II only
C)III only
D)I and II only
E)I, II, and III

Accepted Answer

Adding an element with one additional or one fewer valence electron (doping) can increase conductivity by introducing more charge carriers. Lowering the temperature generally decreases conductivity in semimetals.

Quiz 9: Molecular Geometry: Shape Determines Function

Light-emitting diodes are semiconductors that emit light when a current is passed through them. What is the key factor that must be changed to change the wavelength of the emitted light in an LED?

Band theory of bonding in solids ________

Which of the following elements are semiconductors? C, Si, Ge, Sn

Which statement about a semiconductor is not correct?

Which element would be used to dope germanium to produce an n-type semiconductor?

Electrical and thermal conductivity in metals ________

Molecular orbital theory can be applied ________

When Ge is doped with Ga, it produces a(n) ________-type semiconductor.

Which element would be used to dope silicon to produce a p-type semiconductor?

Which of the following materials could be classified as a p-type semiconductor?

Metal solids are good conductors of electricity because ________

The molecular orbital description for metal bonding is different from that for diatomic molecules in that ________

The band structure of semiconductors differs from that of metal conductors in that ________

GaAs and AlGaAs2 are examples of ________ semiconductors.

When silicon is doped with gallium, electrical conduction increases because ________

When Si is doped with P, it produces a(n) ________-type semiconductor.

Which statement regarding the electronic structure of solids is not correct?

Which of the following materials could be classified as an n-type semiconductor?

Which statement A-D regarding semiconductors is not correct?

Which of the following can be used to increase the conductivity of any semimetal? I.adding an element with one additional valence electron II.adding an element with one fewer valence electron III.lowering the temperature

GaAs and AlGaAs₂ are examples of ________ semiconductors.