Traditional spectrometers play a crucial role in scientific and industrial research. However, their bulky size and weight have limited their applications in laboratory optical systems, automotive electronic systems, industrial inspection equipment, and smartphones. Therefore, the development of a miniaturized and intelligent spectrometer has become a hot topic in current research.
A team led by Chen Baile and Yu Jingyi from the School of Information Science and Technology at ShanghaiTech University has successfully developed a single-pixel intelligent micro spectrometer based on an AlGaAs/GaAs gradient bandgap PN junction detector. This spectrometer, combined with the Neural Spectral Fields (NSF) spectral reconstruction method, achieves high optical sensitivity, spectral accuracy, and spectral resolution in measurements.
Figure 1: Smart Miniature Spectrometer
This spectrometer achieves dynamic adjustment of detector response cutoff wavelength by changing the bias voltage of the PN junction. Additionally, the research team has customized a Neural Spectral Fields (NSF) spectral reconstruction method for the spectrometer. This method extracts deep features from the measured current-voltage curves and reconstructs continuous spectra through Neural Fields (NFs).
Structure Overview and Electrical Performance of Gradient Bandgap PN Junction Spectrometer
The gradient bandgap PN junction spectrometer, as illustrated in Figure 2, comprises several key components that collectively enable its functionality and performance. This device operates based on the principle of utilizing a PN junction with a gradually changing bandgap to spectrally resolve incident light.
Structure Components:
Substrate: The foundation of the spectrometer, typically made of semiconductor material such as silicon.
P-Doped Layer: The portion of the substrate that is doped with positively charged carriers, creating a PN junction.
N-Doped Layer: Adjacent to the P-doped layer, this section of the substrate is doped with negatively charged carriers, forming the PN junction necessary for light detection.
Gradient Bandgap Region: The interface between the P-doped and N-doped layers, characterized by a gradual transition in bandgap energy. This region enables the spectrometer to capture a broad range of wavelengths effectively.
Electrical Contacts: Contacts placed on the P and N regions allow for the application of an external voltage, facilitating the operation of the PN junction.
Electrical Performance:
Spectral Resolution: The ability of the spectrometer to distinguish between different wavelengths of light, influenced by factors such as the width and gradient of the bandgap region.
Responsivity: A measure of the spectrometer's sensitivity to incident light, determined by the efficiency of carrier generation and collection within the PN junction.
Dark Current: The current that flows through the PN junction in the absence of light, affecting the signal-to-noise ratio and overall performance of the spectrometer.
Dynamic Range: The range of light intensities over which the spectrometer can accurately measure spectral information, influenced by factors such as linearity and saturation of the device's response.
Temperature Dependence: The sensitivity of the spectrometer's electrical characteristics to changes in temperature, which can impact its performance and stability in various operating conditions.
In summary, the gradient bandgap PN junction spectrometer offers a versatile platform for spectral analysis, leveraging its unique structure and electrical properties to achieve high-resolution and sensitive detection of light across a broad range of wavelengths.
The imaging results and array design of the Gradient Bandgap PN Junction Spectrometer
Through this neural spectroscopic field reconstruction method, the Gradient Bandgap PN Junction Spectrometer achieves a spectral reconstruction accuracy of up to 0.30nm and a spectral resolution of up to 10nm. The spectral range is extensive, covering from 480nm to 820nm. This spectrometer is fabricated using standard III-V semiconductor processes, reaching the micron level, with the potential for large-scale production and integration. It is also compatible with focal plane array (FPA) fabrication processes, enabling further advancement towards high-spectral imaging in the future.
Figure 4: Spectral Measurement Process and Results of Gradient Bandgap PN Junction Spectrometer
This research breakthrough offers new insights and methods for miniaturizing and intelligentizing spectrometers, potentially advancing the application and development of spectral technology in various fields. Moreover, the manufacturing process of this spectrometer is compatible with the fabrication process of focal plane arrays (FPAs), laying a foundation for future hyperspectral imaging technology. The intelligent microspectrometer holds promise for significant roles in environmental monitoring, food safety, biomedicine, and other fields, providing more possibilities for scientific research and industrial applications.
This achievement has been published in Nature Communications. Professor Baile Chen and Professor Jingyi Yu from the School of Information Science and Technology at ShanghaiTech University are the corresponding authors. Jingyi Wang, a doctoral student from the class of 2020, Beibei Pan, a master's student from the class of 2021, and Zi Wang, a doctoral student from the class of 2019, are the joint first authors of this work. The device fabrication for this research was supported by the Center for Quantum Devices at ShanghaiTech University.
Title of the Paper:
Single-pixel p-graded-n junction spectrometers
Paper Link:
https://doi.org/10.1038/s41467-024-46066-5
