Previous research in infrared sensing mainly focused on narrow bandgap semiconductor materials, tunable bandgap two-dimensional (2D) materials. However, it is challenging to integrate them with silicon electronics due to lattice mismatch with silicon. To address this challenge, this work proposes a concept of infrared detection different from that of narrow bandgap semiconductors and 2D materials. In this study, thin metal/semiconductor Schottky devices were fabricated to realize mid-infrared light detection by collecting thermal signals generated by hot carriers with energy lower than the Schottky barrier. Experimental results demonstrate successful detection of mid-infrared light signals at wavelengths of 3.22 μm, 4.28 μm, and 4.83 μm, surpassing the cutoff wavelength corresponding to Schottky barrier. Such Schottky devices exhibit a maximum responsivity of 0.680 mA/W, which confirms their efficiency and application potential in application of mid-infrared optical detection.
KEYWORDS: Nanoparticles, Silver, Metals, Photodetectors, Signal to noise ratio, Scanning electron microscopy, Localized surface plasmon resonances, Film thickness, Mid infrared, Electric fields
Due to their tunable bandgap, compound semiconductors have become the primary materials for synthesizing infrared (IR) photodetectors. However, the manufacturing processes for most compound semiconductors are costly and energyintensive. Therefore, developing a low-cost, low-energy, and silicon-compatible IR photodetector is worthwhile. Here, we create an inverted pyramid structure (IPS) for Ag/n-Si photodetector and utilize its structure to enhance localized surface plasmon resonance (LSPR). A thick metal surface makes the hot carriers take a long time to pass through, while the short lifetime of the hot carriers leads to their decay before reaching the destination. Thus thick metal could result in degraded signals. However, examination of the response from the mid-infrared light at 4.26 μm, the 10nm-Ag/n-Si Schottky photodetectors show that the device with a thickness of 14 nm has a 2.6 times improvement in response compared to devices with a thickness of 10 nm, and the signal-to-noise ratio (SNR) increased by 3.6 times. Based on the results of scanning electron microscopy (SEM), the hot carrier effect and the variation of optical response intensity are found to depend highly on the space and size of nanoparticles (NPs). As a result, LSPR enhances light absorption and improves the optical response.
Localized surface plasmon resonance (LSPR) from metal nanoparticles (NPs) has been widely applied to enhance the performance of photodetectors and has been studied by many groups. Due to the limitation of the bandgap, silicon-based (Si-based) devices encounter challenges in sensing infrared region. To overcome this issue, this study discusses how the silver (Ag) NPs to modify Si-based Schottky photodetectors and enhance mid-infrared (MIR) responsivity via rapid thermal annealing (RTA) process by inducing LSPR when illuminating. Under an incident light source at 3460 nm wavelength, the responsivity of the device annealing at 175°C is increased from 0.4481 mA/W to 0.6872 mA/W, which is enhanced 1.533 times compared to device without annealing. In addition, using COMSOL software for electric field intensity simulation confirms that Ag NPs can indeed enhance the electric field intensity to increase the induced LSPR. Therefore, it is demonstrated that the response signal of MIR can be enhanced and amplified by Ag NPs in Schottky devices under the same measurement conditions, achieving the ability to detect MIR region in Si-based Schottky devices.
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