A lead sulfide cell is sensitive to______?

A lead sulfide cell is sensitive to______?

• A. Infrared rays
• B. Ultraviolet rays
• C. Visible light
• D. Microwaves

Answer: (A)

Photons can only create free charge carriers in a semiconductor if their energy is at least the material’s bandgap. Lead sulfide has a very small bandgap, about 0.37 eV at room temperature, which corresponds to infrared wavelengths (roughly around 3 micrometers). When infrared photons are absorbed, electron‑hole pairs form and the material’s conductivity changes, giving a measurable signal. That’s why a lead sulfide cell is sensitive to infrared radiation. Very low‑energy photons (like microwaves) don’t have enough energy to bridge the gap, and while ultraviolet photons carry more energy, PbS detectors are optimized for infrared response, not UV detection.

Photons can only create free charge carriers in a semiconductor if their energy is at least the material’s bandgap. Lead sulfide has a very small bandgap, about 0.37 eV at room temperature, which corresponds to infrared wavelengths (roughly around 3 micrometers). When infrared photons are absorbed, electron‑hole pairs form and the material’s conductivity changes, giving a measurable signal. That’s why a lead sulfide cell is sensitive to infrared radiation. Very low‑energy photons (like microwaves) don’t have enough energy to bridge the gap, and while ultraviolet photons carry more energy, PbS detectors are optimized for infrared response, not UV detection.