The nanopore-structure YBa2Cu3O7 (YBCO) high-temperature superconducting detectors are novel with their possible phase transition mechanism from insulating to metallic states. In this paper, an array of YBCO nanopore detectors were fabricated and evaluated. Very thin YBCO films were deposited on strontium titanate substrates, and 16×1 high-temperature superconducting detectors were prepared by photolithography, etching and evaporation processes. Connected with the specially designed and developed readout circuit, the detectors were tested in terms of resistance-temperature (R-T) and voltage-current (I-V) characteristics. The R-T curve confirms the insulating phase of the nanopore superconducting YBCO film at low temperature. With increasing the incident intensity of 1550nm light, the resistance of the detector reduces significantly, implying the photoinduced metallic-conduction phase. The photoresponse is detectible under 1550 nm irradiation down to ~10nW, suggesting the possibility of highly sensitive photodetection. Our new devices may have application prospects in many fields such as quantum communication and aerospace detection.
This article reports a multi-gain-stage avalanche photodiode based on InGaAs/InAlAs superlattice, which has much higher gain and signal-to-noise ratio than conventional APD. The physical mechanism of high gain and low noise of this type of APD is analyzed in detail, and the dead space gain theory (DSMT) is introduced and applied to the calculation of the excess noise factor of multi-gain-stage APD. For a 5-stage device, the distribution of electric field and carrier dead space is calculated, and the ionization rates before and after considering phonon scattering are compared. The gain vs excess noise factor curve is obtained and compared with the traditional McIntyre model. The simulation results shows that the excess noise factor is equivalent to the McIntyre model k=0.049. Based on the simulation results, an optimized epitaxial material structure is designed, Front-illuminated photo diode were etched in the molecular beam epitaxy (MBE)-grown epitaxial material, the mesa sidewalls were encapsulated with Si3N4 . The test results of a 50μm diameter device are as follows: maximum above 1000, excess noise factor of 2.39@M=100, spectral response range of 0.95~1.65μm, response time of 1.26ns.
InGaAs-based p-i-n Photo-Detectors (PDs) on misoriented Si and conventional Si substrates are both designed, fabricated, and characterized. It is found that the as-grown PD structure on misoriented Si substrate has lower dislocation density than on conventional Si substrate. The PD fabricated on misoriented Si substrate shows a low dark-current of 83nA under −5 V, a zero bias voltage responsivity of 0.58 A/W at 1550 nm, the corresponding quantum efficiency is 46%. The dark-current and quantum efficiency at 1550 nm, of the PD on misoriented Si substrate, is about over one orders of magnitude lower and 70% higher respectively, than the comparison PD fabricated on conventional Si substrate.
InGaAs/InP Negative Feedback Avalanche Diode (NFAD), with a quenching negative feedback resistor integrated, is a new type of high-sensitivity and all-solid-state semiconductor device based on Single Photon Avalanche Diode (SPAD) structure. This paper proposes a near-infrared free-running single photon counting integrated module based on InGaAs/InP NFAD. It contains an active quench and extraction circuit, sampling and processing circuit, upper computer software design and TEC etc., and is designed to serve a NFAD adopting absorption-attenuation-charge-multiplication (SAGCM) structure with InGaAs/InP materials and operating in Geiger mode. In this module, we specifically design a full differential amplifier and comparator to exploit the performance of NFAD by detecting and extracting the weak avalanche signal and converting it into TTL pulse. The avalanche detection discrimination threshold voltage is adjustable by external high-precision DAC, and a programmable dead time could be set by Field Programmable Gate Array (FPGA). The module system provides timing logic in order to avoid false counting caused by the coupling noise of the differential amplifier. By developing Graphical User Interface (GUI) program, we are able to setup detector working parameters configuration, to display real-time counting data and to further meet different application requirements. The fabricated module exhibits good NFAD performance with PDE of 7.9% and 15.8%, DCR of 1.37 kHz and 1.06 kHz and the after-pulse probability of 34.2% and 16.8% at 223 K, 1550 nm with dead time of 200 ns and 1 μs, respectively. It turns out that a near-infrared single photon counting system possessing fast detection speed, fast quenching time, flexible dead time adjustment, small size and high integration will be available in the near future to strongly support lidar and quantum information facilities.
The near-infrared InGaAs/InP avalanche photodiode (APD) is a key device in the field of communication, lidar, resource exploration, etc, but it often suffers from the low absorption coefficient around 1550 nm. Thermal carriers excited by surface plasmons (SPs) have extensive development prospects in photoelectric detection and application because of its unique optical properties. Using the properties of SPs to enhance light absorption, it is applicable to improve the performance of traditional InGaAs/InP APD in the form of metallic two-dimension hole arrays on the detector. In this paper, finite-difference time-domain (FDTD) method was used to simulate the SP enhancement effects on APD. The control variable method was used to study the influence of the parameter of metallic two-dimension hole arrays on transmission and light field distribution. The results indicate the high localization of the SPs and enhanced absorption at 1550 nm, supporting the development of photodetectors towards high sensitivity and high responsivity even using traditional devices.
Two-dimensional III-V binary compounds are considered as high-performance optoelectronic materials due to their tunable bandgap and unique photoelectric properties. In this research, the effects of strain engineering on the electronic properties and optical properties of hexagonal boron phosphide monolayer have been systematically studied by using first principles calculations. The bandgap is enlarged monotonously while the direct bandgap character remains as the strain increases from -10% (compression) to +10% (tension), suggesting its application prospect in flexible electronics. Interestingly, the hexagonal boron phosphide monolayer exhibits a large optical absorption coefficient in both visible and ultraviolet regions and could reach 1.3 × 106 cm-1 in ultraviolet region. As compressive strain gets larger, the main peak of dielectric function as well as the edge of optical absorption appear redshift. In addition, the absorption spectrum broadens in visible light region and the light absorption intensity becomes larger in ultraviolet range with increasing compressive strain. The calculated optical properties prove that hexagonal boron phosphide monolayer is a suitable material as ultraviolet-visible dual band photodetectors and a potential auxiliary material for quantum cutting.
Negative feedback avalanche diode (NFAD) has the advantages of fast quenching speed, low afterpulsing and easy integration. It can be used in quantum communication, fluorescence spectrum detection, single-photon counting imaging and other applications. The research on NFAD devices and their application in single-photon detecting system has thus been of great significance. This paper describes the novel design of NFAD, and reviews the development and application of NFAD devices in recent years. By monolithically integrating a film resistance onto single photon avalanche diode (SPAD), the formed self-passive quenching circuit in NFAD brings about improvements in especially afterpulsing, and effectively enables photon number resolution. Further hybridizing active quenching circuit, the single-photon detection system composed of NFAD performs much better than that of conventional SPAD. NFAD demonstrates more practical application potential so that it will be much more powerfully developed in the future, as we prospect finally in this paper.
This paper summarizes the research progress of SiGe preparation technology at home and abroad, summarizes the advantages and disadvantages of low-voltage silicon epitaxy and molecular beam epitaxy, and discusses the applications of SiGe Heterojunction materials in pin, APD and waveguide laser detectors. Based on the development of black silicon preparation technology at home and abroad, femtosecond laser, wet etching and dry etching are discussed, and their applications in laser detectors are reviewed. Finally, the development prospects of the two materials and their application prospects are summarized and prospected, and the follow-up development direction is given.
To realize the near-infrared detection of silicon-based detectors and avoid the incompatibility between III-V photodetectors and silicon-based integrated circuits, the development of Ge/Si detectors has become a research hotspot, with the breakthrough of preparation technology of Ge / Si heterojunction materials. In this paper, the research progress of Ge / Si heterojunction photodetectors in the wavelength range of 1.1μm to 1.6μm is summarized from the aspects of the device structure, working principle, the current situation at home and abroad, the advantages and disadvantages, and so on.
The self propagating welding of Kovar and sapphire was carried out with NiAl nano multilayers. The samples were tested by X-ray machine, scanning acoustic microscope, scanning electron microscope and bonding tester. The results show that sapphire and Kovar can be well self propagating welded using multilayer NiAl nano multilayers as heat source and solder to form uniform weld joint. The void ratio of the weld joint is 1.1%, and the welding strength is ~ 3.38 MPa. This study lends credible the welding of sapphire and similar metal materials.
A series of two-dimensional TiX2 (X=Cl, Br, I) monolayers and their corresponding van der Waals heterostructures were predicted by the first-principle calculations. The dynamic and thermodynamic stability of TiX2 (X=Cl, Br, I) monolayers are confirmed by the phonon spectra and molecular dynamics simulations, respectively. The Heyd-Scuseria-Ernzerhof-based band values are 0.311-0.989 eV, showing the tunable transition probability between valence and conduction band. Additionally, the significant visible-light absorption coefficient (~ 105 cm-1) and high power conversion efficiency (~12%) of TiBr2/TiCl2 heterojunctions provide promising potentials for solar cells.
The dynamic population processes of infrared radiation in dysprosium-doped different host materials (LaF3, Y2O3, YAlO3 and silicate glass) are theoretically investigated. The radiation and non-radiation transition rates of each energy level are calculated using Judd-Ofelt (J-O) theory and according to “energy-gap law”. It is demonstrated that the non-radiative transition rate increases significantly as the phonon energy increases, indicating that the choice of host materials has a great influence on the infrared transition processes. By solving the rate equations we establish, it is found that the population profiles of the same energy levels are almost the same, but the time to reach equilibrium population varies greatly among different materials. The population probability of 6H9/2 and 6H11/2 energy levels increases first and then decreases, whereas that of 6H13/2 and 6H15/2 monotonically increases or decreases with time. The excited state 6H13/2 has a quite long decay lifetime of 38.97 ms in dysprosium-doped LaF3, which is a good metastable state for mid-infrared emission.. These results are helpful to the material selection and application of infrared lasers.
Transmission properties of transverse magnetic light through periodic sub-wavelength slit apertures on a metallic film, behind which is another planar metallic film, are studied by finite-difference-time-domain method with constant periodicity and slit width. The result shows that the transmitted energy is strongly correlated to both the thickness of the metallic grating and the distance between such two films at a specific wavelength. The thickness of the grating acts as a filter that allows specific wavelengths to go through the slits, while the distance of dual metallic film dominantly determines a constructive or destructive interference between the transmitted light through the slits and the reflected wave from the back film. Besides, a strong vibration in the transmission spectrum as a function of the grating thickness is interestingly observed, which can be interpreted by the resonance of the surface plasmons of the front and the back metallic films.
Impact ionization in charge layer and multiplication layer of InAlAs/InGaAs avalanche photodiodes (APDs) with separated absorption, grading, charge and multiplication structures has been studied by two-dimensional simulations using Silvaco TCAD. Special attention has been paid to the charge layer and multiplication layer with different thicknesses and doping concentrations in order to optimize the structure for low band discontinuities and an appropriate electric field distribution. Band-edge profile calculations as well as current–voltage characteristic and electric field results of the APDs will be discussed in this article.
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