surface photovoltage spectroscopy

**SPV** (Surface Photovoltage Spectroscopy) is a **contactless technique that measures the change in surface potential when the sample is illuminated** — providing carrier properties, surface band bending, defect energy levels, and minority carrier diffusion lengths. **How Does SPV Work?** - **Dark**: The semiconductor surface has an equilibrium band bending (surface potential $V_s$). - **Illuminated**: Photo-generated carriers reduce the band bending -> surface photovoltage = $Delta V_s$. - **Spectroscopy**: Sweep the photon energy -> SPV onset reveals the bandgap. Sub-gap signals indicate defect levels. - **Measurement**: Kelvin probe or capacitive coupling detects the change in surface potential. **Why It Matters** - **Non-Contact**: Completely non-contact, non-destructive measurement of minority carrier properties. - **Diffusion Length**: SPV vs. photon penetration depth gives minority carrier diffusion length. - **Defect Spectroscopy**: Sub-bandgap SPV identifies defect energy levels and their cross-sections. **SPV** is **shining light on surface electronics** — measuring how illumination changes the surface potential to reveal carrier and defect properties.