Moderate-temperature thermal sources often radiate waste heat as a by-product of mechanical work, chemical or nuclear reactions, or information processing. In a new report in Science, Paul S. Davids and a research team at the Sandia National Laboratory in the U.S., demonstrated the conversion of thermal radiation into electrical power. For this, they used a bipolar grating-coupled complimentary metal-oxide-silicon (CMOS) tunnel diode. Using a two-step photon-assisted tunneling charge pumping mechanism, the team separated the charge carriers in pn junction wells to develop a large, open-circuit voltage across a load. The scientists experimentally showed electrical power generation from a broadband blackbody thermal source with converted power densities of 27 to 61 µW/cm2 for thermal sources between 250 degrees C to 400 degrees C. The demonstrated scalable and efficient conversion of radiated waste heat into electrical power can be used to reduce energy consumption—in order to power electronics and sensors.