Energy Band Gap by Four Probe Method
1. What is a semiconductor?
- A material that completely blocks electric current
- A type of metal used only in circuits
- A material with electrical conductivity between a conductor and an insulator
- A perfect conductor of electricity
2. What is an energy band?
- A region of vacuum between atoms
- A band of light waves in the visible spectrum
- A large number of closely spaced energy levels in a small energy range
- The difference between conduction and valence band
3. What is the valence band?
- The highest energy band filled with valence electrons
- The lowest unfilled energy band
- A band above the conduction band
- A band containing only free electrons
4. What is the conduction band?
- The highest filled energy band
- The lowest unfilled allowed energy band next to the valence band
- A forbidden region in semiconductors
- The band containing holes only
5. What is the energy band gap or forbidden energy gap?
- The gap between the top of the valence band and bottom of the conduction band where no electron states exist
- A band of overlapping energy levels
- A gap inside the conduction band
- The region occupied by valence electrons
6. What is Fermi level and Fermi Energy?
- The lowest energy state in the conduction band
- The highest energy level filled with electrons at absolute zero; its energy is Fermi Energy
- The energy difference between two atoms
- The maximum kinetic energy of moving electrons
7. What are holes?
- Vacuum regions in the lattice
- Free protons inside a semiconductor
- The absence of an electron in the bond of a covalently bonded crystal
- Electrons with negative charge
8. What are intrinsic and extrinsic semiconductors?
- Intrinsic semiconductors cannot conduct electricity
- Intrinsic have impurities; extrinsic are pure
- Intrinsic are metals; extrinsic are insulators
- Intrinsic are pure semiconductors; extrinsic are doped to form p-type or n-type materials
9. What is a p-type and n-type semiconductor?
- p-type is always negative; n-type is always positive
- p-type conducts only heat; n-type conducts only electricity
- p-type has trivalent impurities with holes as majority carriers; n-type has pentavalent impurities with electrons as majority carriers
- Both have only electrons as charge carriers
10. What are p-n-p and n-p-n transistors?
- p-n-p has holes only; n-p-n has electrons only
- Both are made from pure semiconductors
- p-n-p has an n-layer between two p-layers; n-p-n has a p-layer between two n-layers
- They are types of resistors
11. What is the use or working of a four-probe method in the instrument?
- All probes are used to measure resistance directly
- Probes measure magnetic field instead of voltage
- Outer probes pass current; inner probes measure voltage using a voltmeter
- All four probes are used for voltage measurement
12. What is the formula for measuring resistivity using four-probe method?
- ρ = VI × s
- ρ = (V/I) × 2πs for thick samples; modified by a factor F(w/s) for thin samples
- ρ = (I/V) × s²
- ρ = V + I × s
13. How is the band gap of a semiconductor calculated?
- By calculating average energy of conduction electrons
- Using the formula ln ρ = E₉ / 2kT and plotting ln ρ versus 1/T
- By directly measuring voltage across the sample
- Using the formula E = mc²
14. Why doesn’t using the correction factor in resistivity calculations affect the band gap value?
- Because it affects only the temperature, not resistivity
- Because it changes the shape of the energy band
- Because the correction factor is always zero
- Because the correction factor is constant and does not affect the slope of the ln ρ vs 1/T graph
