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Semiconductors and Superconductivity: Foundations of Modern Technology
Semiconductor Physics
Band Structure
- Silicon Bandgap: 1.12 eV at 300K
- GaAs Bandgap: 1.42 eV (direct bandgap)
- Carrier Concentration:
(Si, 300K)
Doping Techniques
| Type | Dopant | Carriers | Concentration Range |
|---|---|---|---|
| n-type | Phosphorus (Si) | Electrons | 10¹⁴-10²⁰ cm⁻³ |
| p-type | Boron (Si) | Holes | 10¹⁴-10²⁰ cm⁻³ |
Superconductivity Fundamentals
BCS Theory
- Cooper pairs form below Tc
- Critical temperature equation:
Type I vs Type II
| Property | Type I | Type II |
|---|---|---|
| Materials | Pure metals | Alloys/Compounds |
| Tc Range | < 10K | Up to 138K (HgBaCaCuO) |
Cutting-Edge Applications
Quantum Computing
- Superconducting qubits operate at ~15 mK
- Coherence times: 50-100 μs (2023)
Power Grid Innovations
- REBCO tapes carry 500 A/mm² at 77K
- Superconducting fault current limiters respond in <5 ms
Neuromorphic Chips
- Memristors emulate synapses (10¹² ops/J)
- Phase-change materials for analog computing
Worked Example
Solar Cell Parameters:
- Current: 5 A
- Voltage: 10 V
- Efficiency: 22%
![\[ P_{out} = IV = 50 \, \text{W} \]](https://i0.wp.com/on22.com/wp-content/ql-cache/quicklatex.com-f4bc77f169a0d6c1f0abc4a83abecc82_l3.png?resize=141%2C15&ssl=1 "Rendered by QuickLaTeX.com")
![\[ P_{in} = \frac{P_{out}}{\eta} = \frac{50}{0.22} \approx 227 \, \text{W solar input} \]](https://i0.wp.com/on22.com/wp-content/ql-cache/quicklatex.com-a80c9c3400321e8119d98baeb2e198e5_l3.png?resize=305%2C42&ssl=1 "Rendered by QuickLaTeX.com")
Critical Thinking Questions
- Explain how the Meissner effect enables maglev trains to achieve stable levitation
- Compare electron mobility in Si (1500 cm²/Vs) vs GaAs (8500 cm²/Vs)
- Calculate the London penetration depth for Nb (λL ≈ 39 nm)
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