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.