photoluminescence

**PL** (Photoluminescence) is a **non-destructive optical technique that analyzes light emitted from a semiconductor after optical excitation** — the emission spectrum reveals band gap, impurity levels, defect transitions, quantum well properties, and alloy composition. **How Does PL Work?** - **Excitation**: A laser (typically above-gap: 325 nm, 405 nm, 532 nm) excites electron-hole pairs. - **Emission**: Carriers recombine radiatively, emitting photons at characteristic energies. - **Detection**: Spectrometer + detector (Si CCD, InGaAs array, or PMT) analyzes the emission spectrum. - **Cryogenic**: Low-temperature PL (4-10 K) resolves fine spectral features (bound excitons, donor-acceptor pairs). **Why It Matters** - **Material Quality**: PL intensity and linewidth directly indicate material quality and defect density. - **Band Gap**: Directly measures the optical band gap and identifies sub-gap defect transitions. - **Non-Destructive**: Completely non-contact, non-destructive — the primary optical characterization for semiconductors. **PL** is **making semiconductors shine** — using laser light to reveal band structure, impurities, and material quality through emitted luminescence.