30 Questions
What is a characteristic of a Schottky diode?
Low forward voltage drop
What type of contact is formed when a metal and a semiconductor are joined?
Either rectifying or ohmic contact
What is the Fermi Level?
The highest energy level that an electron can occupy
What is the purpose of a band diagram in understanding Schottky diodes?
To illustrate the energy level of electrons
What is the result of applying a forward voltage to a Schottky diode?
Current flow in the forward direction
What is the name of the contact formed between a metal and a semiconductor?
Schottky barrier contact
What is the energy difference between the conduction band minimum and the vacuum energy level?
Electron affinity
What is the term for the energy required to take an electron from the Fermi level and give it enough energy to escape to infinity?
Work function
What is the type of contact used in a Schottky diode for switch applications?
Unipolar contact
What is the symbol used to represent the work function in semiconductors?
Фs
What is the location of the Fermi level in a n-type semiconductor?
Close to the conduction band
What is the purpose of a Schottky diode when used as a rectifier contact?
To allow current flow in one direction
What is the primary characteristic of the Schottky barrier?
Barrier height
What is the result of electrons transferring from the semiconductor to the metal under equilibrium conditions?
A negative charge in the metal and a positive charge in the semiconductor
What is the role of the built-in-voltage in a Schottky barrier?
To prevent the movement of electrons from the semiconductor to the metal
What is the relationship between the Schottky barrier height and the Fermi energy of the metal?
ΦB = ΦM - χ
Why is the width of the depletion region primarily present inside the n-type semiconductor?
Because the metal has a sea of free electrons
What is necessary for the conduction band electrons of the n-type semiconductor to overcome the built-in-voltage?
Energy greater than the built-in-voltage
What is the primary characteristic of a Schottky barrier?
It is a depletion layer formed at the metal-semiconductor junction
What happens when a metal and a semiconductor material are brought together?
An instant ideal MS contact is formed without electron movement
What is the significance of the work function of semiconductors?
It is related to the electron affinity and the conduction band
What is the condition for the formation of a Schottky contact?
φm φs
What is the function of a Schottky barrier in a diode?
It is the potential energy barrier that electrons must overcome to flow across the diode
What is the type of semiconductor that can form a Schottky contact?
Both n-type and p-type semiconductors
What is the primary reason that prevents further electron flow from the n-type semiconductor to the metal in an unbiased Schottky diode?
The built-in-voltage
What happens to the potential barrier across the semiconductor when a forward bias is applied to the MS junction?
It decreases
What is the direction of the current generated across the MS junction when a forward bias is applied?
From the semiconductor to the metal
What happens to the depletion region when the applied voltage is continuously increased in a forward-biased MS junction?
It becomes very thin and finally disappears
What is the effect of the reduction of the potential barrier on the flow of electrons across the MS junction?
It makes it easier for electrons to pass over the barrier
What is the result of the transfer of free electrons from the n-type semiconductor to the metal in an unbiased Schottky diode?
Energy band bending near the contact
Study Notes
Fermi Level and Energy Bands
- Fermi level changes as solids are warmed and electrons are added to or withdrawn from the solid
- Fermi level lies close to the conduction band and valence band in a n-type and p-type semiconductor
Work Function
- Measures the energy required to take an electron from the Fermi energy level to infinity (vacuum) with zero energy
- Represented as Фm for metals and Фs for semiconductors
- Measured in terms of voltage
Electron Affinity
- Measures the energy required to capture an electron and convert it to a negatively charged ion
- Energy difference between the conduction band minimum (CBM) and the vacuum energy level
- Denoted by χ and measured in terms of voltage
Schottky Diode
- A type of metal-semiconductor diode with a low forward voltage drop and fast switching speed
- Formed by joining a metal and a semiconductor, resulting in a rectifying contact (Schottky barrier contact)
- Allows current to flow in one direction when enough forward voltage is applied
Schottky Barrier
- A depletion layer formed at the junction of a metal and n-type semiconductor
- Potential energy barrier that electrons must overcome to flow across the diode
- Characterized by the Schottky barrier height, ΦB = ΦM - χ, for n-type semiconductor
Working of a Schottky Diode
- Under equilibrium conditions, electrons transfer from the semiconductor to the metal, creating a depletion region and a growing barrier
- The built-in-potential (built-in-voltage) is primarily present inside the n-type semiconductor
- To overcome the barrier, free electrons need energy greater than the built-in-voltage
Forward Biasing
- When the applied voltage is increased (VA > 0), the Fermi energy of the metal becomes lower than the Fermi energy in the semiconductor
- The potential barrier ΦB across the semiconductor is reduced, making it easier for electrons to pass over the barrier
- The current increases rapidly as more electrons diffuse from the semiconductor to the metal
Reverse Biasing
- When the applied bias is negative (VA < 0), the depletion region becomes wider, and the current decreases
Learn about the Schottky Diode, a type of metal-semiconductor diode with low forward voltage drop and fast switching speed. Understand the two possible types of contact between metal and semiconductor, including rectifying and ohmic contacts.
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