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.
Based on the measured I-V curve of the Ag/n-Si Schottky photodetector, it can be verified that the Ag / n-Si Schottky photodetector can detect the NIR band. The responsivity of the photodetector without or with applied bias can be analyzed by the measured I-V curve. Furthermore, we eventually succeed in applying a pulse signal on the voltage source to resolve the thermal disturbance generated by the external voltage and also optimize the responsivity of the Ag/n-Si Schottky photodetector.
The accurate determination of the azimuth of a given direction, e.g., the true (geographic) North, is of fundamental importance in many fields. Just as few examples, it guides buildings construction in civil engineering, supports environmental and cartographic surveys, allows the correct positioning and stability control of concentrating solar power plants, as well as of airport installations, provides the geographic North reference for geomagnetic measurements, contributes to the interpretation of the orientation choices of ancient constructions in archeoastronomy, can be the primary benchmark to calibrate other compasses or gyroscopes. When aiming at reaching azimuth measurements with accuracies well below 1°, magnetic compasses are unreliable: firstly, they indicate the magnetic North rather than the geographic one; secondly, they are heavily influenced by possible surrounding ferromagnetic items.
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