Radiation Hardness of 4H-SiC P-N Junction UV Photo-Detector

4H-SiC based p-n junction UV photo-detectors were irradiated with 600 keV He+ in the fluence range of 5 × 1011 ÷ 5 × 1014 ion/cm2 in order to investigate their radiation hardness. The effects of irradiation on the electro-optical performance were monitored in dark condition and in the UV (200 ÷ 400 nm) range, as well as in the visible region confirming the typical visible blindness of unirradiated and irradiated SiC photo-sensors. A decrease of UV optical responsivity occurred after irradiation and two fluence regimes were identified. At low fluence (<1013 ions/cm2), a considerable reduction of optical responsivity (of about 50%) was measured despite the absence of relevant dark current changes. The presence of irradiation induced point defects and then the reduction of photo-generated charge lifetime are responsible for a reduction of the charge collection efficiency and then of the relevant optical response reduction: point defects act as recombination centers for the photo-generated charges, which recombine during the drift/diffusion toward the electrodes. At higher irradiation fluence, the optical responsivity is strongly reduced due to the formation of complex defects. The threshold between low and high fluence is about 100 kGy, confirming the radiation hardness of SiC photo-sensors.

Towards high performance near-infrared photo detectors based on SnS nanowires

Compared with bulk structures, semiconductor nanowires exhibit a higher surface-to-volume ratio, as well as unique electrical and optical properties. Due to its narrow band gap, tin (ii) sulfide (SnS) nano wire is a promising candidate for constructing near-infrared (NIR) photodetectors. Uniformly distributed and well aligned SnS nanowires were grown on mica substrate by chemical vapor deposition, and NIR photodetectors with Au (Au-device) and Al (Al-device) as the electrode were fabricated and characterized. Compared to Au-device, Al-device achieved higher photodetectivity due to reduced dark current. More importantly by incorporating photosensitive lead phthalocyanine (PbPc) film into Al-device, both responsivity and detectivity could be apparently improved, especially at weak light intensities. Under a weak light intensity of 0.79 mW/cm2 the photoresponsivity and specific detectivity were improved from ~0.56 A/W and 5.1×1010 Jones to 0.96 A/W and 8.4×1010 Jones, respectively.

Measurement of absolute light yield and quantum efficiency of LaBr3:Ce scintillator detector using SiPM

This brief communication presents our work to determine the absolute light yield and quantum efficiency of LaBr3:Ce scintillator by comparison and also by direct pulse measurement method using SiPM. The first part presents use of the simpler comparison method to determine the light yields of different scintillators using the known yield of NaI(Tl) as reference. In the second part we have determined the absolute light yield and quantum efficiency of LaBr3:Ce crystal by using a SiPM photo detector. Our measured value is in good agreement with the light yield reported by previous measurements using PMT and excitation fluorescence spectroscopy. Quantum efficiencies for scintillation detectors have been determined by using both PMTs and photo detectors, namely APDs by previous authors. This communication is possibly the first report on the determination of quantum efficiency of LaBr3:Ce using SiPM photo detector. The simple and effective method presented here would allow to determine the light yield of any scintillation detector.

Acousto-optic Light Pulse Shaper for Measuring the Parameters of Photo-detectors

The paper emphasizes that intensive utilization of the optical range increases the need for the development of new optoelectronic devices. Accordingly, there is a growth in the need for effective methods and tools to study photoelectric properties of semiconductor materials, including photo-detectors.In the paper we have analyzed the well-known methods and tools for measuring the photo-detector parameters, defined the restrictions in their applications, and proved that it is relevant to create a measuring system, the parameters of which are easily adapted to the study of photoelectric characteristics of a wide range of semiconductor materials, including photo-detectors.The scheme and principle of operation of the acousto-optic processor and the features of the photo-elastic effect are discussed, and it is proved that they can be used to form a light pulse of required duration and power. The expressions obtained for calculating the response at the acousto-optic processor output enable us to estimate separately the effects of time of crossing the optical beam by the elastic wave packet and the photo-detector inertia.The capability to determine the time of crossing the optical beam by the elastic wave packet and taking it into account as a device error has been substantiated. The proposed formulas have been tested and by numerical analysis based on the datasheet specifications of the FD-24K photodiode, the effectiveness of the obtained expressions has been convincingly proven.The inertia parameters of a particular sample of the FD-24K photodiode are experimentally studied. The emphasis is upon measuring the rise time of the transient response of the object under study. The exact rise time value of the transient response of the experimental FD-24K sample was approximately 7 μs, which is less than that indicated (≤10 μs) in the product certificate. In real life, such a measurement is necessary when selecting the photodiode pairs with identical parameters.By comparing the results of numerical analysis and experimental studies, it has been convincingly proven that the features of the photo-elastic effect can be used to construct a light pulse shaper with the required parameters.

Triple-Band Anisotropic Perfect Absorbers Based on α-Phase MoO3 Metamaterials in Visible Frequencies

Anisotropic materials provide a new platform for building diverse polarization-dependent optical devices. Two-dimensional α-phase molybdenum trioxides (α-MoO3), as newly emerging natural van der Waals materials, have attracted significant attention due to their unique anisotropy. In this work, we theoretically propose an anisotropic perfect metamaterial absorber in visible frequencies, the unit cell of which consists of a multi-layered α-MoO3 nanoribbon/dielectric structure stacked on a silver substrate. Additionally, the number of perfect absorption bands is closely related to the α-MoO3 nanoribbon/dielectric layers. When the proposed absorber is composed of three α-MoO3 nanoribbon/dielectric layers, electromagnetic simulations show that triple-band perfect absorption can be achieved for polarization along [100], and [001] in the direction of, α-MoO3, respectively. Moreover, the calculation results obtained by the finite-difference time-domain (FDTD) method are consistent with the effective impedance of the designed absorber. The physical mechanism of multi-band perfect absorption can be attributed to resonant grating modes and the interference effect of Fabry–Pérot cavity modes. In addition, the absorption spectra of the proposed structure, as a function of wavelength and the related geometrical parameters, have been calculated and analyzed in detail. Our proposed absorber may have potential applications in spectral imaging, photo-detectors, sensors, etc.