The photothermoelectric effect is a photoelectric detection mechanism that uses the thermal effect generated by light and combines the thermoelectric response properties of materials to generate electrical signals. It has the advantages of zero external-bias operation, broadband optical response, and no bandgap limitation. Thus, the photothermoelectric effect has potential applications in infrared and terahertz photodetection. With the potential impact on the efficient utilization of hot carriers in nanomaterials and the demand for long-wave detection at room temperature, research on the photothermoelectric effect has rapidly advanced in recent years, with new materials and novel device designs emerging in this field. However, the mechanism, simulation, measurement methods of relevant material parameters, design guidelines, and detection performance of photodetectors based on the photothermoelectric effect still urgently need to be clarified and summarized in this field to deepen our understanding and enrich research tools.
Progress Starting from the physical mechanism of the photothermoelectric effect, we systematically examined the factors influencing the photothermoelectric effect, such as the Seebeck coefficient, carrier mobility, optical absorption efficiency, and thermal properties. We reviewed the conductivity and Seebeck coefficient improvement method by adjusting the bandgap and effective mass of the carrier density of states through energy band engineering. We presented a theoretical formula and experimental method for optimizing the thermoelectric figure of merit by regulating the material selection, nanostructures, phonon spectrum, and thermal conductivity. The physical mechanism of the photogenerated carrier process was also discussed. We presented experimental differentiation methods for the photothermoelectric and photovoltaic effects (Fig. 2), clarifying the different electromotive forces and photocurrent origins. We introduced a detailed multiphysical simulation model of the photothermoelectric effect using COMSOL finite-element simulation software and discussed the critical parameters for improving the photothermoelectric response. We summarized the experimental methods for measuring the material conductivity, Seebeck coefficient, thermal conductivity, thermoelectric merit, bandgap, carrier mobility, concentration, effective mass, and carrier scattering mechanism. We reviewed the research progress in photodetectors under the photothermoelectric effect in the past three years, particularly in one-dimensional carbon nanotubes, Ⅲ-Ⅴ semiconductor nanowires, two-dimensional materials, and materials with phonon-polariton characteristics. The performance of the photodetectors based on the photothermoelectric effect is summarized in Table 1. We introduced the optical, electrical, and thermal design guidelines, critical performance parameters, and recent applications of photothermoelectric effect photodetectors.
Conclusions and Prospects Photothermoelectric effect photodetectors exhibit advantages of broadband optical response, nonexternal bias, and room-temperature operating conditions. Thus, they have promising applications in the visible, infrared, and terahertz photodetector regions. The photothermoelectric effect can also be applied to photovoltaics, material characterization, spintronics, and valleytronics. Before the bright application prospect, several vital problems remain to be solved for the photothermoelectric effect, such as the response speed, synergy effect of the photothermoelectric/photovoltaic effect, and optimization of thermoelectric materials with high carrier mobility. With continual research efforts in photothermoelectric effect photodetectors, extended applications based on the photothermoelectric effect are expected.
Photodetection is essential for obtaining optical information and computation. Photothermal and photoelectric detectors are two types of detectors that are widely used because of their different utilization advantages. The advantages of photothermal detectors include their broad spectral response and the ability to function at room temperature. The disadvantages of photothermal detectors include their relatively low detection speed and efficiency compared to photoelectric detectors. Photoelectric detectors exhibit high sensitivity and rapid response, but their material bandgap limits the detectable wavelength and typically requires operation under cryogenic conditions for small photon energy. The key scientific and technological demand is to overcome the bandgap limitation of materials and achieve room-temperature light detection in mid- and far-infrared and even terahertz bands. Therefore, investigations of related materials, mechanisms, and device design principles are urgent.
