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.
A Schottky infrared photodetector with dual mechanisms, where both photoelectric and photothermal current generation mechanisms coexist is presented. The dominant role of these mechanisms changes with surface passivation process. In the device without passivation process, the device exhibits high responsivity due to the presence of the photothermal effect but has slow rise and recovery times. However, after surface passivation treatment, the device characteristics are dominated by the photoelectric effect, showing a significantly faster response time, capable of detecting signal level changes within less than 80 ms, with a constant current difference between on and off states. This unique multifunctionality promotes the development of Schottky device capable of achieving multiple optical detection purposes
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.
The metal-semiconductor interface structure, which can convert photon energy into electrons by internal photon-emission effect, is utilized as one kind of photodetectors. In the Schottky device, the barrier limits the detectable wavelength and the detection response, so how to amplify the detection signal is an important issue. Here, we first quantify the effect of applied bias on the energy barrier reduction mechanism from a mathematical equation. Furthermore, we fabricate metal/semiconductor Schottky devices and experimentally demonstrate the optimization of optical response by image-force lowering effect. As a result, experiment showed a 21 times enhancement in responsivity after an image-force lowering effect was induced.
The Cr/n-Si Schottky interface can effectively extend the cutoff wavelength of the silicon-based device. The estimated barrier height, ideality factor, and series resistance are obtained by characteristic curves and thermionic-emission formula. In order to improve the accuracy of the estimation, a method of adjusting the external resistance in the experimental setup was proposed in this paper. Eventually, the Cr/n-Si Schottky device was well analyzed with an estimated error of < 0.05 in the resistance value, and the results also confirmed that the detection wavelength of the silicon-based components could be extended to mid-infrared range.
Nowadays, compound semiconductors are the main approach to detect mid-infrared (IR) light, such as HgCdTe and InAsSb, due to the bandgap tunability compared with Si. However, the epitaxy processes are expensive and energy-intensive. Also, compound devices are not compatible with Si-based IC manufacturing. To solve those problems, here, we apply inverted pyramid array structures (IPAS) to induce localized surface plasmon resonance (LSPR) for Si-based Schottky devices. While IR illuminates metal covered IPAS (metal-IPAS), the photo-electrons can accumulate photon energy repeatedly through IPAS induced LSPR. While the electron energy is large enough to overcome the Schottky barrier, so the photo-current is generated. Regarding device preparation and measurement, briefly, the IPAS were formed on n-type Si (n-Si) substrates through photolithography, dry etching, and wet etching. Afterward, 10-nm-thick Ag films and 100-nm-thick Ag grid anode were thermally deposited on the IPAS successively to form Schottky junctions. Finally, Al was thermally deposited on the back of n-Si wafers to be the cathode. After device fabrication, the devices were illuminated by a 4010 nm mid-IR pulse laser, generated from a 1064 nm pulse laser through an optical parametric generator. The photo-voltage of the device induced by the mid-IR was measured by an oscilloscope. Consequently, the oscilloscope showed a short pulse while the device was illuminated by the 4010 nm pulse laser. The rising time is 8 ns, and the amplitude is 10.2 mV. The result reveals that the metal-IPAS induced LSPR successfully detects mid-IR light with photon energy less than Schottky barrier height.
Infrared (IR) photodetector is widespread applied to spectroscopy, biosensing, and image detection. Nowadays, most of IR photodetectors are prepared from compound semiconductors, for example, SiGe, HgCdTe, and InSb. However, most of them are formed through high energy consumption and high expense processes, such as chemical vapor deposition. Also, compound devices are not compatible with Si-based IC manufacturing and very expensive. Therefore, here, we used n-type Si (n-Si) wafers and Ag thin films to form a Schottky IR detector. The detection principle is using IR source to induce thermionic effect on Schottky diode and then the scattering of photoelectrons excited by IR and visible light, respectively, induces current difference. Regarding device preparation, at first, the native oxide on n-Si wafers was removed by buffer HF; then the 10-nm-thick Ag films and 100-nm-thick Ag grid anode were thermally deposited on the n-Si successively. Afterward, Al was thermally deposited on the opposite side of n-Si wafers to be a cathode. The electric property of devices was determined through current-to-time (I-T) measurement with an 80-mW green laser illuminating on the Ag side constantly. A 3.22-μm IR source was illuminated through Ag side but turned on/off for each 5 s. The electric bias is 0 V. Consequently, if no green laser exposing, current increased after IR turned on due to the pure thermionic effect and the responsivity is 1.8 mA/W. While the green laser illuminating constantly, current decreased after IR turned on, and the responsivity increased to -15.7 mA/W.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.