Visible-ultraviolet dual-band photodetectors based on an all-inorganic CsPbCl3/p-GaN heterostructure.

All-inorganic metal halide perovskites (MHPs) have attracted increasing attention because of their high thermal stability and band gap tunability. Among them, CsPbCl3 is considered a promising semiconductor material for visible-ultraviolet dual-band photodetectors because of its excellent photoelectric properties and suitable band gap value. In this work, we fabricated a visible-ultraviolet dual-band photodetector based on a CsPbCl3/p-GaN heterojunction using the spin coating method. The formation of the heterojunction enables the device to exhibit obvious dual-band response behavior at positive and negative bias voltages. At the same time, the dark current of the device can be as low as 2.42 × 10-9 A, and the corresponding detection rate can reach 5.82 × 1010 Jones. In addition, through simulation calculations, it was found that the heterojunction has a type II energy band arrangement, and the heterojunction response band light absorption is significantly enhanced. The type II energy band arrangement will separate electron-hole pairs more effectively, which will help improve device performance. The successful implementation of visible-ultraviolet dual-band photodetectors based on a CsPbCl3/p-GaN heterojunction provides guidance for the application of all-inorganic MHPs in the field of multi-band photodetectors.

Broadband Photodetector for Ultraviolet to Visible Wavelengths Based on the BA2PbI4/GaN Heterostructure.

Two-dimensional (2D) organic-inorganic hybrid perovskites (OIPs) have exhibited ideal prospects for perovskite photodetectors (PDs) owing to their remarkable environmental stability, tunable band gap, and structural diversity. However, most perovskites face the great challenge of a narrow spectral response. Integrating 2D OIPs with a suitable wide band gap semiconductor gives opportunities to broaden the response spectra. Here, a photodetector based on the BA2PbI4/GaN heterostructure with a broadband photoresponse covering from the ultraviolet (UV) to visible band is designed. We demonstrate that the device is capable of detecting in the UV region by p-GaN being integrated with BA2PbI4. The morphology and material optical properties of BA2PbI4 are characterized by transmission electron microscopy (TEM) and photoluminescence (PL). Additionally, the current-voltage (I-V) characteristics and photoresponses of the BA2PbI4/GaN heterojunction photodetector are investigated. The response spectrum of the photodetector is broadened from the visible to UV region, exhibiting good rectifying behavior in the dark conditions and a broadband photoresponse from the UV to the visible region. Additionally, the energy band is used to analyze the current mechanism of the BA2PbI4/GaN heterojunction PD. This study is expected to provide a new insight of optoelectronic devices by integrating 2D OIPs such as BA2PbI4 and wide-band-gap semiconductors such as GaN to broaden the response spectra.

Metal-semiconductor-metal solar-blind ultraviolet photodetector based on Al0.55Ga0.45N/Al0.4Ga0.6N/Al0.65Ga0.35N heterostructures.

We have designed a metal-semiconductor-metal (MSM) solar-blind ultraviolet (UV) photodetector (PD) by utilizing Al0.55Ga0.45N/Al0.4Ga0.6N/Al0.65Ga0.35N heterostructures. The interdigital Ni/Au metal stack is deposited on the Al0.55Ga0.45N layer to form Schottky contacts. The AlGaN hetero-epilayers with varying Al content contribute to the formation of a two-dimensional electron gas (2DEG) conduction channel and the enhancement of the built-in electric field in the Al0.4Ga0.6N absorption layer. This strong electric field facilitates the efficient separation of photogenerated electron-hole pairs. Consequently, the fabricated PD exhibits an ultra-low dark current of 1.6 × 10-11 A and a broad spectral response ranging from 220 to 280 nm, with a peak responsivity of 14.08 A/W at -20 V. Besides, the PD demonstrates an ultrahigh detectivity of 2.28 × 1013 Jones at -5 V. Furthermore, to investigate the underlying physical mechanism of the designed solar-blind UV PD, we have conducted comprehensive two-dimensional device simulations.

Resolution and signal-to-noise ratio enhancement for synthetic coded aperture imaging via varying pinhole array.

In traditional coded aperture imaging (CAI), the main problem with the deconvolution method is that the noise may dominate the decoding process. Focusing on this problem, a synthetic CAI (s-CAI) method is proposed with a potential to improve the signal-to-noise ratio (SNR) and spatial resolution of CAI. A series of raw coded images are recorded while the pinhole array is varied to different structures, and an iterative decoding algorithm is developed to reconstruct the object image by synthetically using all of these pinhole array structures and corresponding decoded images. Because the proposed iterative decoding algorithm has prominent advantage in noise immunization, and more spatial light components are acquired in comparison with common single-exposure CAI, both the image resolution and SNR are remarkably enhanced.

The Sensitivity of Grating-Based SPR Sensors with Wavelength Interrogation.

In this paper, we derive the analytical expression for the sensitivity of grating-based surface plasmon resonance (SPR) sensors working in wavelength interrogation. The theoretical analysis shows that the sensitivity increases with increasing wavelength and is saturated beyond a certain wavelength for Au and Ag gratings, while it is almost constant for Al gratings in the wavelength range of 500 to 1000 nm. More importantly, the grating period (P) and the diffraction order (m) dominate the value of sensitivity. Higher sensitivity is possible for SPR sensors with a larger grating period and lower diffraction order. At long wavelengths, a simple expression of P/|m| can be used to estimate the sensor sensitivity. Moreover, we perform experimental measurements of the sensitivity of an SPR sensor based on an Al grating to confirm the theoretical calculations.

Partial saturation-aided resolution enhancement for digital holography.

Because of the limited dynamic range of common detectors, high-frequency components weaker than the threshold of the detector used are lost in digital holography (DH) even with the aid of coherent diffraction imaging (CDI)-based iterative computation, and this makes DH less preferable for many interesting applications. To overcome this problem, the partially saturated diffraction pattern was adopted to enhance the resolution of DH iteratively. Since more high-frequency components were retrieved in comparison with our former CDI-based digital holographic method, the resolution of DH was improved further. The feasibility of the proposed method is demonstrated both numerically and experimentally.