Hot electron detectors and energy conversion in the UV and IR

Abstract

Semiconductor materials are well suited for power conversion when the incident photon energy is slightly larger than the bandgap energy of the semiconductor. However, for photons with energy significantly greater than the bandgap energy, power conversion efficiencies are low. Further, for photons with energy below the bandgap energy, the absence of absorption results in no power conversion. Here we describe photon detection and power conversion of both high energy and sub-bandgap photons using hot carrier effects. For the absorption of high-energy photons, excited electrons and holes have excess kinetic energy, which results in the generation of hot electrons and holes. Energy is typically lost through a thermalization process between the carriers and the lattice. However, collection of carriers before thermalization allows for reduced power loss. Devices consisting of a three-layer stack (transparent conductor – insulator – metal) can be used to generate and collect these hot carriers. Alternatively, when a semiconductor is used, photons with energy below the semiconductor bandgap energy generally do not generate electrons and holes; however, hot carrier collection is still possible in semiconductor devices with a metal layer when a Schottky junction is formed at the semiconductor-metal interface. Such structures enable IR detection based on sub-bandgap photon absorption. Combining these concepts, hot carrier generation and collection and be exploited over a large range of incident wavelengths spanning the UV, visible, and IR.