This topic covers the basic properties of semiconductor materials, including the concept of energy bands, bandgap, doping, and intrinsic vs. extrinsic semiconductors.
Introduction to Semiconductor Materials
Key concepts, classifications, properties, and applications
| Aspect | Description |
|---|---|
| Definition | A material whose electrical conductivity lies between that of a conductor (e.g., copper) and an insulator (e.g., glass). |
| Band Theory | At absolute zero the valence band is full and the conduction band is empty. A modest energy gap (≈0.1–3 eV) separates them, allowing electrons to be thermally or optically excited into the conduction band. |
| Intrinsic vs. Extrinsic | Intrinsic – pure crystal, conductivity determined solely by temperature. Extrinsic – doped with impurity atoms, conductivity controlled by carrier concentration. |
| Material | Crystal Structure | Bandgap (eV) | Typical Use |
|---|---|---|---|
| Silicon (Si) | Diamond cubic | 1.12 (indirect) | Micro‑electronics, solar cells |
| Germanium (Ge) | Diamond cubic | 0.66 (indirect) | High‑speed transistors, infrared detectors |
| Gallium Arsenide (GaAs) | Zincblende | 1.42 (direct) | RF/microwave, optoelectronics (LED, laser) |
| Silicon Carbide (SiC) | Hexagonal (4H, 6H) | 3.2 (indirect) | Power devices, high‑temperature sensors |
| Gallium Nitride (GaN) | Wurtzite | 3.4 (direct) | LEDs, high‑electron‑mobility transistors (HEMT) |
| Indium Phosphide (InP) | Zincblende | 1.34 (direct) | Photonic integrated circuits |
| CdTe, CIGS, Perovskites | Various | 1.0–1.6 (direct) | Thin‑film photovoltaics |
| Property | Symbol | Typical Value (Si, 300 K) | Influence |
|---|---|---|---|
| Carrier concentration (intrinsic) | (n_i) | (1.5 \times 10^{10},\text{cm}^{-3}) | Increases exponentially with temperature |
| Electron mobility | (\mu_n) | ~1400 cm²/V·s | Higher mobility → faster device operation |
| Hole mobility | (\mu_p) | ~450 cm²/V·s | Lower than electrons in Si |
| Resistivity | (\rho) | 10 kΩ·cm (intrinsic) | Reduced by doping (down to mΩ·cm) |
| Conductivity | (\sigma = q (n\mu_n + p\mu_p)) | — | Directly proportional to carrier density and mobility |
Key equations
| Dopant Type | Added Element (Si example) | Created Carrier | Energy Level (relative to