1. What is a tunnel junction?
a) A junction formed between two conductive materials separated by an insulating barrier
b) A junction where electrons can easily pass through without resistance
c) A junction used for blocking the flow of current
d) A junction formed between a metal and a semiconductor
Answer: a) A junction formed between two conductive materials separated by an insulating barrier
Explanation: A tunnel junction consists of two conductive materials separated by a thin insulating barrier. This setup allows electrons to tunnel through the barrier, overcoming the potential energy barrier without requiring a significant amount of energy.
2. Which of the following is an application of tunneling through a potential barrier?
a) Quantum cryptography
b) Nuclear fusion
c) Semiconductor doping
d) Magnetic resonance imaging
Answer: a) Quantum cryptography
Explanation: Tunneling through a potential barrier is utilized in quantum cryptography, where it enables secure communication by allowing particles to pass through barriers that would be classically impassable.
3. What type of junction is formed between a metal and an insulator?
a) Metal-semiconductor junction
b) Metal-insulator junction
c) Insulator-semiconductor junction
d) Semiconductor-insulator junction
Answer: b) Metal-insulator junction
Explanation: A metal-insulator junction is formed between a metal and an insulator, where the insulator acts as a barrier to the flow of electrons.
4. Coulomb blockade primarily affects the behavior of:
a) Photons
b) Electrons
c) Protons
d) Neutrons
Answer: b) Electrons
Explanation: Coulomb blockade refers to the phenomenon where the flow of electrons through a small conducting region is hindered due to the repulsive Coulomb interaction between electrons.
5. In which structure does Coulomb blockade occur in a nanoscale device?
a) Quantum well
b) Quantum dot
c) MOSFET
d) Bipolar junction transistor
Answer: b) Quantum dot
Explanation: Coulomb blockade is often observed in nanoscale devices such as quantum dots, where the discrete energy levels and the charging energy of the dot play a significant role in electron transport.
6. What type of junction is formed in a metal-semiconductor-metal configuration?
a) p-n junction
b) Tunnel junction
c) Schottky junction
d) Ohmic contact
Answer: c) Schottky junction
Explanation: In a metal-semiconductor-metal configuration, a Schottky junction is formed between the metal and the semiconductor, which exhibits rectifying behavior due to the difference in work functions between the two materials.
7. Which phenomenon describes the inhibition of tunneling current due to the repulsion of charges?
a) Quantum confinement
b) Coulomb blockade
c) Bandgap modulation
d) Spintronics
Answer: b) Coulomb blockade
Explanation: Coulomb blockade occurs when the repulsive Coulomb interaction between charges inhibits the tunneling current through a small conducting region.
8. What happens to the tunneling current in a tunnel junction excited by a current source as the applied voltage increases?
a) It decreases exponentially
b) It increases linearly
c) It remains constant
d) It oscillates
Answer: a) It decreases exponentially
Explanation: In a tunnel junction excited by a current source, as the applied voltage increases, the tunneling current decreases exponentially due to the increasing energy barrier for tunneling.
9. Which of the following junctions is commonly used in electronic devices for its rectifying behavior?
a) Metal-metal junction
b) Semiconductor-semiconductor junction
c) Metal-insulator-metal junction
d) Metal-semiconductor junction
Answer: d) Metal-semiconductor junction
Explanation: Metal-semiconductor junctions, such as Schottky diodes, exhibit rectifying behavior and are commonly used in electronic devices for applications like rectifiers and detectors.
10. What is the primary factor determining the tunneling probability in a tunnel junction?
a) Electron charge
b) Barrier thickness
c) Temperature
d) Voltage
Answer: b) Barrier thickness
Explanation: The tunneling probability in a tunnel junction primarily depends on the thickness of the insulating barrier between the two conductive materials. Thinner barriers allow for higher tunneling probabilities.