Keywords: Photocurrent Mapping Self-curling Detector Photothermoelectric Effect Lock-in Amplifier
Note: This post uses the Sine Scientific Instruments OE1022 lock-in amplifier to make measurement.
[Overview]
In July 2024, a research paper entitled "Enhanced photothermoelectric conversion in self-rolled tellurium photodetector with geometry-induced energy localization" was published by Yongfeng Mei/Gaoshan Huang of the Department of Materials Science, Fudan University, in the important optical journal Light: Science & Applications. Enhanced photothermoelectric conversion in self-rolled tellurium photodetector with geometry-induced energy localization". In this study, tellurium nanofilms, which are photothermoelectric active materials, were separated from the substrate and assembled into three-dimensional tubular self-driven photodetectors by using the self-roll-up technique, revealing the localization of optical and thermal energies as well as the mechanism of photothermoelectric conversion in three-dimensional scales of the devices, realizing the broadband optical detection and sensitivity enhancement, and providing an effective solution for the multi-dimensional photoelectric detection.
Localized optical and thermal energy for efficient photothermoelectric conversion is essential for high-performance photothermoelectric detection. However, the study of micro- and nanoscale devices in the presence of coupled multiphysics fields, especially the substrate effects, is facing challenges. With the development of on-chip integrated devices to three dimensions, the constitutive relations of three-dimensional micro-nano devices need to be deeply explored. The construction of independent three-dimensional micro-nano structures using nanofilm stripping technology can effectively localize photothermal energy and provide important support for device practicality.
[Measurement methods and some experimental results]
The research team used photothermally active materials and reassembled nanofilms detached from the substrate into a three-dimensional convoluted structure through self-curling nanotechnology, which utilizes the longitudinal internal strain gradient of the nano films (Fig. 1a). This structure is able to concentrate the light field energy in the overhanging 3D tube wall due to the resonance effect (Fig. 1b), leading to a larger temperature difference, which in turn generates a significant potential difference during the thermoelectric conversion process. The experimental results further validate the remarkable effect of this Self-rolled Tubular Tellurium-based Detector (hereafter TTD) on the enhancement of the light detection performance, with a 307-fold enhancement of the self-driven photogenerated voltage realized.
Fig.1 The research team used photothermally active materials and reassembled nanofilms detached from the substrate into a three-dimensional convoluted structure through self-curling nanotechnology, which utilizes the longitudinal internal strain gradient of the nano films (Fig. 1a). This structure is able to concentrate the light field energy in the overhanging 3D tube wall due to the resonance effect (Fig. 1b), leading to a larger temperature difference, which in turn generates a significant potential difference during the thermoelectric conversion process.
The team delved into the photothermoelectric effect and its position dependence in self-curling detectors. Figure 2(a-b) demonstrates the mapping between the position of the incident light and the intensity and direction of the generated photogenerated current within the self-curling photothermoelectric device, thus confirming the coupling and conversion efficiency of the photo-thermal-electricity in the three-dimensional structure. Fig. 2(c) demonstrates a good linear relationship between the self-driven photogenerated voltage (Vph) and the incident optical power density (Pλ) of the TTD under laser irradiation of different wavelengths, which confirms the sensitivity of the TTD to light and the ability of self-driven photodetection in a wide wavelength range. Figure 2(d) demonstrates the variation of voltage responsivity (RV) of the TTD with incident optical power density (Pλ) under laser irradiation at different wavelengths. Under 940 nm laser irradiation, the RV of the TTD reaches 252.13 V W-1, which is a very high value, indicating that the TTD has a very high photothermoelectric conversion efficiency at this wavelength. In summary, the TTD demonstrates its ability to realize self-driven light detection over an ultra-wide range of wavelengths from the visible to the long-wave infrared.The self-driven nature of the TTD means that it can be operated without the need for an external power supply, which facilitates portable and remote light detection applications.
Fig.2 Verification of the photothermoelectric effect of the self-curling detector: a-b. Spatial coordinate system used for the study, as well as schematic and experimental results of the position dependence of the photogenerated currents; c-d. Curves of incident optical power versus the self-driven photogenerated voltage, voltage responsivity, under multiwavelength excitation.
All photoresponse measurements in this study, including photocurrent mapping, photovoltage line scanning, and other optoelectronic properties, were measured by an MStarter 200 probe stage, a Keysight B2902B, and a lock-in amplifier (OE1022, Sine Scientific Instruments) .
[Summary]
In this study, a novel self-curling 3D photothermoelectric detector was successfully designed and fabricated by employing 3D self-curling nanotechnology and incorporating thermoelectric functional materials. The three-dimensional tubular structure significantly enhances the light absorption and thermal localization effects, and improves the photo-thermal-electrical conversion efficiency by locally concentrating the photo-thermal energy. The self-curling photo-thermoelectric detector not only has high sensitivity and wide spectral response range, but also possesses unique features such as self-driving, omnidirectional detection and polarization imaging, which predicts its potential application in on-chip integrated optoelectronic systems.
[References]
