Semiconductors Practice Questions

Correct answer: Silicon

Silicon is a widely used intrinsic semiconductor because its electrical conductivity lies between that of conductors and insulators. It has four valence electrons, which form covalent bonds in a crystal lattice, allowing controlled conductivity when energy is supplied.

Correct answer: Holes

In intrinsic semiconductors, electrons excited to the conduction band leave behind vacancies called holes in the valence band. Each excited electron creates exactly one hole, so the number of electrons equals the number of holes.

Correct answer: Extrinsic semiconductor

Extrinsic semiconductors are created by introducing impurities into a pure semiconductor through a process called doping. These impurities increase the number of free charge carriers, enhancing conductivity.

Correct answer: Phosphorus

Phosphorus is a pentavalent impurity with five valence electrons. When added to silicon, it contributes an extra free electron, increasing electron concentration and producing an n-type semiconductor.

Correct answer: Electrons

In n-type semiconductors, pentavalent impurities donate extra electrons to the conduction band. As a result, electrons become the majority charge carriers, while holes are the minority carriers.

Correct answer: Boron

Boron is a trivalent impurity with three valence electrons. When doped into silicon, it creates a deficiency of electrons, resulting in holes that act as the majority charge carriers in a p-type semiconductor.

Correct answer: Holes

In p-type semiconductors, trivalent impurities create vacancies called holes in the valence band. These holes behave like positive charge carriers and dominate electrical conduction.

Correct answer: Energy difference between conduction band and valence band

The energy gap, or band gap, is the energy difference between the valence band and the conduction band. Electrons must gain at least this amount of energy to move into the conduction band and contribute to electrical conduction.

Correct answer: Germanium

Germanium has a band gap of about 0.67 eV, compared with roughly 1.1 eV for silicon, about 1.4 eV for gallium arsenide and about 5.5 eV for diamond. The smaller the gap, the less energy an electron needs to reach the conduction band.

Correct answer: Diode

A diode is created by forming a junction between p-type and n-type semiconductors. This p-n junction allows current to flow primarily in one direction, making it useful for rectification.

Correct answer: Depletion region

The depletion region forms near the p-n junction because electrons and holes recombine there. This leaves behind fixed charged ions, creating a region with very few mobile charge carriers.

Correct answer: p-side to positive terminal and n-side to negative terminal

In forward biasing, the p-side is connected to the positive terminal and the n-side to the negative terminal of a battery. This reduces the depletion region barrier and allows current to flow easily.

Correct answer: Becomes wider

Reverse biasing connects the p-side to the negative terminal and the n-side to the positive terminal. This pulls charge carriers away from the junction, increasing the width of the depletion region and restricting current flow.

Correct answer: Transistor

A transistor is a semiconductor device capable of amplifying signals or acting as an electronic switch. It typically consists of three layers forming either an NPN or PNP structure.

Correct answer: Copper

Copper is a metal and a good electrical conductor with freely moving electrons. Semiconductor materials like silicon and germanium have moderate conductivity that can be controlled through doping.

Correct answer: It increases

As temperature increases, more electrons gain enough energy to jump from the valence band to the conduction band. This increases the number of charge carriers and therefore increases conductivity.

Correct answer: Pentavalent doping

Pentavalent doping introduces impurities such as phosphorus or arsenic that have five valence electrons. The extra electron becomes free for conduction, creating an n-type semiconductor.

Correct answer: Majority carriers

Under forward bias, majority carriers move across the junction. Electrons move from the n-side to the p-side, and holes move from the p-side to the n-side, producing current.

Correct answer: Material with conductivity between conductors and insulators

Semiconductors have electrical conductivity between that of conductors and insulators. Their conductivity can be controlled by temperature, light, and doping, making them useful in electronic devices.

Correct answer: Has high electron mobility

Gallium arsenide has higher electron mobility than silicon, allowing electrons to move faster through the material. This property makes it useful in high-speed electronic and optoelectronic devices.