Lecture 1 Quiz

Question 1

Name one elemental semiconductor

Answer 1

One elemental semiconductor is silicon (Si). Silicon is a very common semiconductor material that is used in many electronic devices such as transistors, solar cells, and diodes.

Question 2

Name one compound semiconductor.

Answer 2

One compound semiconductor is gallium arsenide (GaAs). Gallium arsenide is a compound of gallium and arsenic and it is used in high-speed electronic devices such as cell phones and other wireless devices, high-frequency microwave devices, and high-efficiency solar cells. it is also used in some laser diodes, infrared emitting diodes, and light-emitting diodes.

Question 3

Classify materials into 3 groups based on their resistivity

Answer 3

There are three main groups of materials based on their resistivity: conductors (low), semiconductors( intermediate), and insulators (high).

Question 4

What is a conductor

Answer 4

Conductors have a low resistivity, meaning they allow electrical current to flow through them easily. Examples of conductors include metals such as copper and aluminum.

Question 5

What is a Insulator

Answer 5

Insulators have a high resistivity, meaning they do not allow electrical current to flow through them easily. Examples of insulators include rubber and glass.

Question 6

What is a Semiconductor

Answer 6

Semiconductors have a resistivity that is intermediate between conductors and insulators. They are unique in that their resistivity can be manipulated by introducing impurities, a process known as doping, this allows them to be used in electronic devices such as transistors, diodes, and solar cells. Examples of semiconductors include silicon and gallium arsenide.

Question 7

What Semiconductor material used in the Pentium chip

Answer 7

The semiconductor material used in the Pentium chip is silicon (Si) not Germanium (Ge). Silicon is the most widely used semiconductor material, it has a wide range of properties that make it suitable for use in electronic devices such as transistors, diodes, and solar cells. It is also relatively cheap and easily available. Germanium is also a semiconductor material but it has been mostly replaced by silicon in most electronic devices because it has a higher intrinsic carrier concentration and a lower bandgap energy, which makes it less suitable for use in high-performance electronic devices.

Question 8

What is the difference between a crystalline, amorphous and polycrystalline material?

Answer 8

the main difference between these three types of materials is the arrangement of their atoms, ions, or molecules: Crystalline materials have a regularly repeating, three-dimensional arrangement, amorphous materials lack a regularly repeating, three-dimensional arrangement and polycrystalline materials are made up of many small crystals that are randomly oriented.

Question 9

What is a crystalline material

Answer 9

A crystalline material is a material that has a regularly repeating, three-dimensional arrangement of atoms, ions, or molecules. The atoms, ions, or molecules are arranged in a specific pattern, which is known as a crystal lattice. Crystalline materials have a high degree of order and symmetry, which gives them unique physical and chemical properties. Examples of crystalline materials include metals, ceramics, and many minerals.

Question 10

What is a amorphous material

Answer 10

An amorphous material is a material that lacks a regularly repeating, three-dimensional arrangement of atoms, ions, or molecules. Instead, the atoms, ions, or molecules are arranged in a random or disordered pattern. Amorphous materials have a low degree of order and symmetry, which gives them different physical and chemical properties than crystalline materials. Examples of amorphous materials include glass and many polymers.

Question 11

What is a amorphous material

Answer 11

A polycrystalline material is a material that is made up of many small crystals, called grains, that are randomly oriented. The grains in polycrystalline materials are usually smaller than the grains in single-crystalline materials. The properties of polycrystalline materials are intermediate between those of single-crystalline and amorphous materials and are often dependent on the size and distribution of the grains. Examples of polycrystalline materials include some metals, ceramics, and semiconductors.4

Question 12

Give the ratio of the number of holes and the number of conduction electrons in an intrinsic semiconductor

Answer 12

In an intrinsic semiconductor, the ratio of the number of holes (missing electrons) to the number of conduction electrons (free electrons) is equal to one. This is because in an intrinsic semiconductor, the number of electrons that are available to participate in electrical conduction is equal to the number of holes that are available to participate in electrical conduction.

The number of holes and conduction electrons in an intrinsic semiconductor is determined by the thermal energy of the semiconductor. At low temperatures, there are relatively few electrons and holes, so the intrinsic semiconductor is not a good conductor. As the temperature increases, more electrons and holes are created, and the intrinsic semiconductor becomes a better conductor.

It’s worth noting that in extrinsic semiconductors, the ratio of the number of holes and the number of conduction electrons is not equal to one, this is due to the presence of impurities that are added to the intrinsic semiconductor. These impurities create additional holes or electrons, which can change the ratio of holes to electrons and affect the electrical properties of the material.

Question 13

What are n-type semiconductors

Answer 13

n-type semiconductors are created by adding impurities such as phosphorus or antimony to the intrinsic semiconductor. These impurities introduce extra electrons into the semiconductor, making it a better conductor. The material is called an n-type semiconductor because the extra electrons create an excess of negatively charged carriers.

Question 14

What are p-type semiconductors?

Answer 14

p-type semiconductors are created by adding impurities such as boron or aluminum to the intrinsic semiconductor. These impurities create “holes” in the semiconductor, which behave as if they are positively charged particles. These holes make the material a better conductor. The material is called a p-type semiconductor because the holes create an excess of positively charged carriers.

Question 15

What is the difference between n-type and p-type semiconductors?

Answer 15

he main difference between n-type and p-type semiconductors is the type of impurities that are added to the intrinsic

Question 16

Give the ratio of the number of holes and the number of conduction electrons in an intrinsic semiconductor

Answer 16

The ratio of the number of holes and the number of conduction electrons in an intrinsic semiconductor is 1:1. This is because in an intrinsic semiconductor, the number of holes (missing electrons) is equal to the number of conduction electrons (free electrons). This balance is due to the thermal equilibrium that exists in the semiconductor.

Question 17

How does thermal energy affect the conductivity of an intrinsic semiconductor?

Answer 17

At low temperatures, there are relatively few electrons and holes, so the intrinsic semiconductor is not a good conductor. As the temperature increases, more electrons and holes are created, and the intrinsic semiconductor becomes a better conductor.

Question 18

How does the ratio of the number of holes and the number of conduction electrons differ in extrinsic semiconductors?

Answer 18

In extrinsic semiconductors, the ratio of the number of holes and the number of conduction electrons is not equal to one, this is due to the presence of impurities that are added to the intrinsic semiconductor. These impurities create additional holes or electrons, which can change the ratio of holes to electrons and affect the electrical properties of the material.

Question 19

What determines where a material is an insulator, semiconductor, or conductor ?

Answer 19

the classification of materials as insulators, semiconductors, or conductors is based on their electrical conductivity, which is determined by the number of free electrons available to participate in electrical conduction. The electrical conductivity of a material can be influenced by its atomic structure, crystal structure, chemical composition and temperature.

Question 20

The process of adding impurities into crystal is know by …..?

Answer 20

The process of adding impurities into a crystal is known as doping. Doping refers to the intentional introduction of impurities into a semiconductor crystal in order to alter its electrical properties. The impurities are typically added in very small amounts, often in the form of a small number of atoms per billion, but can still have a significant effect on the semiconductor’s electrical properties. There are two main types of doping: N-type doping, where impurities such as phosphorus or arsenic are added to the crystal, which creates additional electrons and increases the number of free electrons. P-type doping, where impurities such as boron or aluminum are added, which creates holes in the crystal and increases the number of free holes. The combination of p-type and n-type doping in a semiconductor crystal is known as a p-n junction, which is a basic building block of many electronic devices such as transistors, diodes and solar cells.

Question 21

What is overall (or net) charge in n-type semiconductor ?

Answer 21

In an n-type semiconductor, the overall or net charge is negative. This is because n-type doping introduces impurities, such as phosphorus or arsenic, into the semiconductor crystal which add extra electrons. These extra electrons increase the number of free electrons in the semiconductor, which makes it a better conductor of electricity.

As a result, the overall or net charge in an n-type semiconductor is negative, because there are more electrons than holes in the crystal. The excess of free electrons gives a negative charge to the material. This is in contrast to a p-type semiconductor, where the overall or net charge is positive due to the majority of holes present in the crystal.

Question 22

Calculate the energy gap in amorphous silicon if it is given that it is transparent to radiation of wavelength greater than 1100 nm.

Answer 22

The energy gap in a semiconductor is the energy difference between the top of the valence band and the bottom of the conduction band. The energy gap is related to the transparency of the semiconductor to radiation of a specific wavelength. In general, the larger the energy gap, the more transparent the semiconductor is to radiation of a specific wavelength.

Given that amorphous silicon is transparent to radiation of wavelength greater than 1100 nm, we can use the relation between energy gap and wavelength of radiation to calculate the energy gap of amorphous silicon.

The relation between energy gap (Eg) and wavelength of radiation (λ) is given by:

Eg = hc/λ

where h is Planck’s constant, c is the speed of light, and λ is the wavelength of radiation.

By substituting the value of wavelength of radiation, we can calculate the energy gap of amorphous silicon.

Eg = (hc) / (1100*10^-9) m

We can calculate the energy gap in electron volt (eV)

Eg = hc / λ = (4.14 * 10^-15 eV.s) * (310^8 m/s) / (110010^-9 m)
= 1.17 eV

So, the energy gap in amorphous silicon is 1.17 eV if it is transparent to radiation of wavelength greater than 1100 nm.

It’s worth noting that amorphous silicon is usually used in thin-film solar cells, where it’s transparency to infrared radiation is an advantage, while crystalline silicon is mostly used in conventional solar cells.