Silicon Heterojunction Photodetector-Based Laser Absorption Spectroscopy Sensing

In this study, we develop a gas detection system by employing a tunable diode laser absorption spectroscopy (TDLAS) and a nanopyramid structure-enhanced silicon heterojunction photodetector (PD). With oxygen as the target gas, the performance of the system is rigorously verified. Our results show that the silicon-based heterojunction PD achieves an impressive signal-to-noise ratio (SNR) of 427.98, significantly higher than the 140.36 of commercial indium gallium arsenides (InGaAs) PD and the 200.29 of commercial silicon PD. Compared to commercial InGaAs PD and silicon PD, our heterojunction PD has approximately 3.3-fold and 2.1-fold higher sensitivity, respectively. In addition, the minimum detection limit (MDL) has been significantly improved, with an MDL of 480 ppm for silicon-based heterojunction PDs, compared to 1500 ppm for commercial PDs and 1043 ppm for commercial silicon PDs. The normalized noise equivalent absorption coefficient of the system was determined to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.466\times 10^{-{11}}$ </tex-math></inline-formula> cm<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}}\cdot \text {W}\cdot \text {Hz}^{-\text {1/2}}$ </tex-math></inline-formula>. The Allan bias analysis results show that the system achieves an accuracy level of 116 ppm in an average of 320 s. These advances underscore the potential of silicon-based heterojunction PD as a highly sensitive element in gas detection systems, marking a major innovation in laser spectroscopic gas detection.