Solar-blind Imaging Research Articles

Amorphous Gallium Oxide-Based Crosstalk-Suppressing Solar-Blind Imaging Array Prepared by One-Step Method.

The solar-blind ultraviolet band presents a unique opportunity for low-background-noise detection due to limited atmospheric light transmission. Especially, with the ability to obtain size, shape and position information on the objects, the solar-blind image sensors are receiving increasing attention. However, because the inhibition of the crosstalk in crossbar arrays induces the complexity of the preparation process, rarely are applicable solar-blind UV imaging arrays reported. This work prepared an amorphous gallium oxide (a-Ga2O3)-based diode with a remarkable rectifier ratio of up to 106. Then an imaging array was prepared by one-step method in that the diodes working as the detection elements and the switching elements inhibiting crosstalk were simultaneously deposited. Moreover, a 2 × 2 crossbar array clearly demonstrates the inhibition of the crosstalk. This work presents a simple and cost-effective method for preparing applicable solar-blind imaging arrays that inhibits crosstalk, promoting the practical application of the Ga2O3-based solar-blind UV detectors.

High-performance single crystal diamond pixel photodetector with nanosecond rise time for solar-blind imaging

Solar-blind ultraviolet imaging detector is widely applied in many commercial and military fields, such as missile warning, guidance, ultraviolet communication, biomedical analysis, and police reconnaissance. High-performance pixel photodetector is the core of imaging technology. Therefore, its construction attracts intensive attentions in recent years. In this work, 8 × 8 planar pixels were constructed on high quality single crystal diamond using ultraviolet direct writing lithography. A typical pixel photodetector in metal-semiconductor-metal (MSM) structure achieved outstanding photo-response properties of a low dark current of 10−13–10−12 A at 50 V, a high light-dark current switching ratio over 105), a high responsivity of 22.6 A/W, and a decent specific detectivity of 4.2 × 1014 Jones. Moreover, the detector has a fast response time of 13 ns. Additional optoelectronic studies demonstrate the strong homogeneity and repeatability of the photodetectors array, enabling it to serve as a reliable solar-blind imaging photodetector with high spatial resolution.

High-performance solar-blind imaging photodetectors based on micrometer-thick β-Ga2O3 films grown by thermal oxidation of gallium

A preparation method for micrometer-sized β-Ga2O3 films was developed. The MSM device has a responsivity greater than 1.7 A W−1 and has good solar-blind ultraviolet imaging performance.

Enhancing the performance of Self-Powered Deep-Ultraviolet photoelectrochemical photodetectors by constructing α-Ga2O3@a-Al2O3 Core-Shell nanorod arrays for Solar-Blind imaging

With the advancement of Ga2O3-based deep-ultraviolet (DUV) photodetectors (PDs), the integration of PDs into array image sensors has become a sought-after objective. However, while solar-blind imaging research primarily revolves around solid-state Ga2O3-based PDs, there remains a significant gap in the exploration of novel photoelectrochemical (PEC) PDs for solar-blind imaging applications. In this study, self-powered solar-blind PEC-PDs with enhanced performance are fabricated based on α-Ga2O3@a-Al2O3 core–shell nanorod arrays (NRAs). Under DUV irradiation and without external bias, the α-Ga2O3@a-Al2O3 devices demonstrate remarkable superiority over α-Ga2O3 devices. When the light intensity was at 0.50 mW cm−2, the photocurrent density notably rises from 4.60 to 11.24 μA cm−2, accompanied by a corresponding increase in responsivity from 9.60 to 22.70 mA W−1. The enhanced performance is attributed to the α-Ga2O3@a-Al2O3 heterostructure, which establishes a built-in electric field facilitating the separation and directed transport of photogenerated carriers at the interface. Moreover, for the first time, a 5 × 5 matrix of α-Ga2O3@a-Al2O3 core–shell NRAs-based PEC-type PDs is employed to demonstrate a proof-of-concept for self-powered solar-blind imaging, capable of effectively capturing the shapes of the letters “C” and “N”. This work underscores the immense potential of Ga2O3-based PEC-type PDs for future large-area solar-blind imaging applications.

Boosting the performance of deep-ultraviolet photodetector arrays based on phase-transformed heteroepitaxial β-Ga2O3 films for solar-blind imaging

Boosting the performance of deep-ultraviolet photodetector arrays based on phase-transformed heteroepitaxial β-Ga2O3 films for solar-blind imaging

Self-powered Pt/a-Ga2O3/ITO vertical Schottky junction solar-blind photodetector with excellent detection performance.

Self-powered solar-blind photodetectors (PDs) are promising for military and civilian applications owing to convenient operation, easy preparation, and weak-light sensitivity. In the present study, the solar-blind deep-ultraviolet (DUV) photodetector based on amorphous Ga2O3 (a-Ga2O3) and with a simple vertical stack structure is proposed by applying the low-cost magnetron sputtering technology. By tuning the thickness of the amorphous Ga2O3 layer, the device exhibits excellent detection performance. Under 3 V reverse bias, the photodetector achieves a high responsivity of 671A/W, a high detectivity of 2.21 × 1015 Jones, and a fast response time of 27/11 ms. More extraordinary, with the help of the built-in electric field at the interface, the device achieves an excellent performance in detection when self-powered, with an ultrahigh responsivity of 3.69 A/W and a fast response time of 2.6/6.6 ms under 254 nm light illumination. These results demonstrate its superior performance to most of the self-powered Schottky junction UV photodetectors reported to date. Finally, the Pt/a-Ga2O3/ITO Schottky junction photodiode detector is verified as a good performer in imaging, indicating its applicability in such fields as artificial intelligence, machine vision, and solar-blind imaging.

Fully-transparent self-powered ultraviolet photodetector based on GaOx/ZnO heterojunction for solar-blind imaging

With the development of fully-transparent electronic materials and energy-efficient photodetectors, self-powered deep-ultraviolet photodetectors that are fully transparent are expected to have a wide range of applications in solar-blind imaging. Here, we present the first investigation of a self-powered, fully transparent Ga2O3 deep-ultraviolet photodetector array for solar-blind imaging. The device is composed of an amorphous Ga2O3/ZnO heterojunction (GaOx/ZnO) with indium tin oxide (ITO) transparent electrodes, which was prepared using a fully magnetron sputtering method. The fully-transparent device demonstrates exceptional performance at both − 5 V bias and 0 V bias, with a high responsivity of 6.5 × 103 A/W and 13 mA/W, respectively, coupled with excellent stability. Moreover, the device is self-powered due to the built-in electric field formed at the interface of GaOx and ZnO, which efficiently drives carrier motion and generates photocurrent. Finally, we demonstrate the feasibility of transparent devices for solar-blind imaging at 0 V bias by constructing a 5 × 4 GaOx/ZnO heterojunction solar-blind photodetector array, which produces a high-contrast image of the target object. This work provides a new strategy for developing Ga2O3-based fully-transparent self-powered photodetector arrays for solar-blind imaging.

A High-Performance ε-Ga2O3-Based Deep-Ultraviolet Photodetector Array for Solar-Blind Imaging.

One of the most important applications of photodetectors is as sensing units in imaging systems. In practical applications, a photodetector array with high uniformity and high performance is an indispensable part of the imaging system. Herein, a photodetector array (5 × 4) consisting of 20 photodetector units, in which the photosensitive layer involves preprocessing commercial ε-Ga2O3 films with high temperature annealing, have been constructed by low-cost magnetron sputtering and mask processes. The ε-Ga2O3 ultraviolet photodetector unit shows excellent responsivity and detectivity of 6.18 A/W and 5 × 1013 Jones, respectively, an ultra-high light-to-dark ratio of 1.45 × 105, and a fast photoresponse speed (0.14/0.09 s). At the same time, the device also shows good solar-blind characteristics and stability. Based on this, we demonstrate an ε-Ga2O3-thin-film-based solar-blind ultraviolet detector array with high uniformity and high performance for solar-blind imaging in optoelectronic integration applications.

Amorphous Ga2O3 Schottky photodiodes with high-responsivity and photo-to-dark current ratio

Schottky photodiodes with sputtered amorphous Ga2O3 (a-Ga2O3) and asymmetric electrodes were fabricated for the first time and achieved excellent performances under 254-nm light illumination with the superhigh responsivity of 1021.8 A W−1, high photo-to-dark current ratio of 2.3 × 106, fast rise/decay response time of 144/208 ms, high detectivity of 1.66 × 1016 Jones, and high external quantum efficiency of 5.0 × 105 %. The excellent solar-blind detection performances are suggested to be attribute to the large concentration of oxygen vacancies, the possible photo released carriers from the deep-level acceptors, and the high film uniformity, while the former two contribute to the high photo carrier concentration, and the latter one contributes to high quality Schottky contact to achieve the low dark current. A 10 × 10 array based on these a-Ga2O3 Schottky photodiodes realized the imaging of a “E” character with high contrast. The results give a feasible way to achieve large area, low cost, high contrast, and high detection sensitivity solar-blind imaging.

Fully Transparent Amorphous Ga2O3-Based Solar-Blind Ultraviolet Photodetector with Graphitic Carbon Electrodes

In recent years, transparent electrode materials have had a positive effect on improving the responsivity of photodetectors by increasing the effective illumination area of devices due to their high transmittance. In this work, by using radio frequency magnetron sputtering and simple mask technology, an amorphous Ga2O3-based solar-blind UV photodetector with graphitic carbon (C) electrodes was created. The device exhibits a high responsivity of 16.34 A/W, an external quantum efficiency of 7979%, and excellent detectivity of 1.19 × 1013 Jones at room temperature under a light density of 5 μw/cm2. It has been proved that C electrodes can replace the traditional noble metal electrode. Additionally, the potential of the transparent photodetector array in solar-blind imaging is explored. We believe that the present study will pave the way for the preparation of a fully transparent and high-response solar-blind ultraviolet photodetector array.

Wafer-sized polycrystalline diamond photodetector planar arrays for solar-blind imaging

A high-quality 2-inch polycrystalline diamond was prepared by MPCVD technique. Photodetector planar arrays were then fabricated from the polycrystalline diamond. Clear solar-blind images have been obtained using the arrays as the sensing unit.

Image converter tubes with diamond photocathodes and electron flow multipliers

The results of investigations of solar-blind image converter tubes (ICTs), sensitive in the vacuum-ultraviolet (VUV) spectral range are presented. Sensitive-conversion layers of photocathodes based on boron-doped polycrystalline diamond films were grown up on sapphire substrates for the first time. Electron flow multipliers (EFMs) were fabricated in the form of diamond grid. Solar-blind VUV ICTs without the EFM are characterized by spectral sensitivity range of 180…250 nm, estimate of the threshold sensitivity value ~10-9 W/Hz0.5 and current sensitivity ~12 - 15 mA/W. Solar-blind VUV ICTs comprising the electron flow multipliers are characterized by extended spectral sensitivity range of 180…270 nm, improved estimate of the threshold sensitivity value 10-11… 5 × 10-12 W/Hz 0.5 and current sensitivity 50 mA/W.

Ga2O3 based multilevel solar-blind photomemory array with logic, arithmetic, and image storage functions.

Photomemories offer great opportunities for multifunctional integration of optical sensing, data storage, and processing into one single device. However, little attention has been paid to photomemories working in the solar-blind region so far, which may have unique advantages of insusceptibility to ambient light and higher capacity. Herein, we propose and demonstrate a Ga2O3 based solar-blind photomemory array with logic, arithmetic, and optoelectronic memory functions. The device shows n-type field effect-transistor performance with an on/off ratio as high as 106, a responsivity of 8 × 103 A W-1, and a detectivity of 1.42 × 1014 Jones, all of which are amongst the best values ever reported for Ga2O3 based photodetectors. Based on the trapping and de-trapping process of holes in Ga2O3, multilevel data storage can be realized from the device. Simultaneously, the optical and electrical mixed basic logic of reconfigurable "AND" and "OR" operations have been realized in a single cell through the co-regulation of solar-blind light and the grid voltage. In addition, the photomemory can perform counting and addition operations, and the photomemory array can be utilized to realize solar-blind image storage. The results suggest that Ga2O3 may have potential applications in high-performance information storage, computing, and communications.

Особенности характеристик солнечно-слепых электронно-оптических преобразователей с алмазными фотокатодами

The results of investigations of solar-blind image converter tubes (ICTs), sensitive in the ultraviolet spectral range are presented. Photocathodes sensitive layers of the ICT are based on boron-doped polycrystalline diamond films were grown up on sapphire substrates for the first time. Spectral range of the ICT sensitivity is 180…250 nm, the threshold sensitivity value without the electron flow multiplier ~ 10-9 W/Hz0.5 and spectral sensitivity ~ 12 - 15 mA/W.

Solar-blind imaging based on 2-inch polycrystalline diamond photodetector linear array

Diamond is a promising ultrawide-bandgap semiconductor, which has drawn much attention in deep-ultraviolet optoelectronics and high-power electronics, due to its unique properties, including the highest thermal conductivity, strong radiation resistance, high breakdown electric field, chemical and thermal stability, and high carrier mobility. However, the optoelectronics applications have been restricted greatly by the small growth size of the single-crystal diamond. In this work, we demonstrate a solar-blind photodetector linear array based on high-quality 2-inch polycrystalline diamond, which has the advantage of large-area growth. The photodetector cells exhibit good uniformity, a responsivity of 45 mA/W at 228 nm with a cut-off wavelength of 240 nm, and a short response time of <20 μs. Clear solar-blind images are obtained by using the photodetector linear array as sensing units. The results reported in this work promise the potential applications of polycrystalline diamond in deep-ultraviolet photodetectors.

Metal–Semiconductor–Metal ε-Ga2O3 Solar-Blind Photodetectors with a Record-High Responsivity Rejection Ratio and Their Gain Mechanism

In recent years, Ga2O3 solar-blind photodetectors (SBPDs) have received great attention for their potential applications in solar-blind imaging, deep space exploration, confidential space communication, etc. In this work, we demonstrated an ultra-high-performance ε-Ga2O3 metal–semiconductor–metal (MSM) SBPD. The fabricated photodetectors exhibited a record-high responsivity and fast decay time of 230 A/W and 24 ms, respectively, compared with MSM-structured Ga2O3 photodetectors reported to date. Additionally, the ε-Ga2O3 MSM SBPD presents an ultrahigh detectivity of 1.2 × 1015 Jones with a low dark current of 23.5 pA under an operation voltage of 6 V, suggesting its strong capability of detecting an ultraweak signal. The high sensitivity and wavelength selectivity of the photodetector were further confirmed by the record-high responsivity rejection ratio (R250 nm/R400 nm) of 1.2 × 105. From the temperature-dependent electrical characteristics in the dark, the thermionic field emission and Poole–Frenkel emission were found to be responsible for the current transport in the low and high electric field regimes, respectively. In addition, the gain mechanism was revealed by the Schottky barrier lowering effect due to the defect states at the interface of the metal contact and Ga2O3 or in the bulk of Ga2O3 based on current transport mechanism and density functional theory calculations. These results facilitate a better understanding of ε-Ga2O3 photoelectronic devices and provide possible guidance for promoting their performance in future solar-blind detection applications.

Ga2O3 photodetector arrays for solar-blind imaging

A multi-channel Ga2O3 photodetector array with 16 cells was fabricated to realize solar-blind imaging.

Self-powered diamond/β-Ga2O3 photodetectors for solar-blind imaging

Self-powered solar-blind photodetectors based on diamond/β-Ga2O3 heterojunctions have been fabricated and high quality solar-blind images have been realized.

Review of using gallium nitride for ionizing radiation detection

With the largest band gap energy of all commercial semiconductors, GaN has found wide application in the making of optoelectronic devices. It has also been used for photodetection such as solar blind imaging as well as ultraviolet and even X-ray detection. Unsurprisingly, the appreciable advantages of GaN over Si, amorphous silicon (a-Si:H), SiC, amorphous SiC (a-SiC), and GaAs, particularly for its radiation hardness, have drawn prompt attention from the physics, astronomy, and nuclear science and engineering communities alike, where semiconductors have traditionally been used for nuclear particle detection. Several investigations have established the usefulness of GaN for alpha detection, suggesting that when properly doped or coated with neutron sensitive materials, GaN could be turned into a neutron detection device. Work in this area is still early in its development, but GaN-based devices have already been shown to detect alpha particles, ultraviolet light, X-rays, electrons, and neutrons. Furthermore, the nuclear reaction presented by 14N(n,p)14C and various other threshold reactions indicates that GaN is intrinsically sensitive to neutrons. This review summarizes the state-of-the-art development of GaN detectors for detecting directly and indirectly ionizing radiation. Particular emphasis is given to GaN's radiation hardness under high-radiation fields.

Development of solar-blind AlGaN 128×128 Ultraviolet Focal Plane Arrays

This paper reports the development of solar-blind aluminum gallium nitride (AlGaN) 128×128 UV Focal Plane Arrays (FPAs). The back-illuminated hybrid FPA architecture consists of an 128×128 back-illuminated AlGaN PIN detector array that is bump-mounted to a matching 128×128 silicon CMOS readout integrated circuit (ROIC) chip. The 128×128 p-i-n photodiode arrays with cuton and cutoff wavelengths of 233 and 258 nm, with a sharp reduction in response to UVB (280–320 nm) light. Several examples of solar-blind images are provided. This solar-blind band FPA has much better application prospect.