Solar-blind Deep-ultraviolet Photodetectors Research Articles

Thermodynamic, electronic, and optical properties of ultra-wide bandgap zirconium-doped tin dioxide from a DFT perspective.

The effects of zirconium doping on the thermodynamic, electronic, and optical properties of tin dioxide are investigated by using density functional theory calculations combined with the cluster expansion method. In the whole composition range, the formation enthalpies of all structures are positive, indicating that SnO2-ZrO2 is an immiscible system and the ZrSnO2 alloy has a tendency of phase separation at low temperature. The x-T phase diagram of ZrSnO2 ternary alloy shows that the critical temperature is 979 K, which means that when the growth temperature of ZrSnO2 crystal is higher than the critical temperature, it is possible to realize the full-component solid solution. The bandgaps of ZrxSn1-xO2 alloys (0 ≤ x ≤ 1) are direct and increase as the Zr composition increases. Zr doping can tune the bandgap of SnO2 from the ultraviolet-B region to the deep ultraviolet region, and has a strong optical response to deep ultraviolet light. The projected density of states and band offsets clearly reveal the reason for the increase of bandgap, which provides useful information to design relevant optoelectronic devices such as quantum wells and solar-blind deep ultraviolet photodetectors.

High-Performance Solar-Blind Ultraviolet Photodetectors Based on β-Ga2O3 Thin Films Grown on p-Si(111) Substrates with Improved Material Quality via an AlN Buffer Layer Introduced by Metal-Organic Chemical Vapor Deposition.

We have achieved significantly improved device performance in solar-blind deep-ultraviolet photodetectors fabricated from β-Ga2O3 thin films grown via metal-organic chemical vapor deposition (MOCVD) on p-Si(111) substrates by improving material quality through the use of an AlN buffer layer. High-structural-quality β-Ga2O3 films with a (-201) preferred orientation are obtained after the introduction of the AlN buffer. Under 3 V bias, the dark current reaches a minimum of 45 fA, and the photo-to-dark current ratio (PDCR) reaches 8.5 × 105 in the photodetector with the metal-semiconductor-metal (MSM) structure. The peak responsivity and detectivity are 38.8 A/W and 2.27 × 1015 cm·Hz1/2/W, respectively, which are 16.5 and 230 times that without the buffer layer. Additionally, benefiting from the introduction of the AlN layer, the photodetection performance of the β-Ga2O3/AlN/Si heterojunction is significantly improved. The PDCR, peak responsivity, and detectivity for the β-Ga2O3/AlN/p-Si photodetector at 5 V bias are 2.7 × 103, 11.84 A/W, and 8.31 × 1013 cm·Hz1/2/W, respectively. The improved structural quality of β-Ga2O3 is mainly attributed to the decreased in-plane lattice mismatch of 2.3% for β-Ga2O3(-201)/AlN(002) compared to that of 20.83% for β-Ga2O3(-201)/Si(111), as well as the elimination of the native amorphous SiOx surface layer on the Si substrate during the initial growth of oxide thin films.

Rapid Response Solar Blind Deep UV Photodetector with High Detectivity Based On Graphene:N/βGa2 O3 :N/GaN p-i-n Heterojunction Fabricated by a Reversed Substitution Growth Method.

This work reports a high-detectivity solar-blind deep ultraviolet photodetector with a fast response speed, based on a nitrogen-doped graphene/βGa2 O3 /GaN p-i-n heterojunction. The i layer of βGa2 O3 with a Fermi level lower than the central level of the forbidden band of 0.2eV is obtained by reversed substitution growth with oxygen replacing nitrogen in the GaN matrix, indicating the majority carrier is hole. X-ray diffractometershows that the transformation of GaN into βGa2 O3 with (-201) preferred orientation at temperature above 900°C in an oxygen ambient. The heterojunction shows enhanced self-powered solar blind detection ability with a response time of 3.2µs (rise)/0.02ms (delay) and a detectivity exceeding 1012 Jones. Under a reverse bias of -5V, the photoresponsivity is 8.3 A W-1 with a high Ilight /Idark ratio of over 106 and a detectivity of ≈9 × 1014 Jones. The excellent performance of the device is attributed to 1) the continuous conduction band without a potential energy barrier, 2) the larger built-in potential in the heterojunction because of the downward shift of Fermi energy level in β-Ga2 O3 , and 3) an enhanced built-in electric field in the βGa2 O3 due to introducing p-type graphene with a high hole concentration of up to ≈1020 cm-3 .

Fully Transparent and High‐Performance ε‐Ga2O3 Photodetector Arrays for Solar‐Blind Imaging and Deep‐Ultraviolet Communication

Fully-Transparent Solar-Blind Photodetectors In article number 2200192, Wanjun Li, Ping-An Yang, Lijuan Ye, and co-workers propose a strategy to construct fully transparent and high-performance solar-blind deep ultraviolet photodetector arrays based on ε-Ga2O3 films using indium tin oxide (ITO), indium gallium zinc oxide (IGZO), and aluminum zinc oxide (AZO) transparent conductive oxides as electrodes. In addition, proof-of-concept ultraviolet imaging and optical communication demonstrate the strong application prospects of ε-Ga2O3-based solar-blind photodetectors in the above fields.

High performance solar-blind ultraviolet photodetector based on ITO/β-Ga2O3 heterostructure

The authors report an indium tin oxide (ITO) decorated solar-blind deep ultraviolet photodetectors (PDs) based on high quality β-Ga2O3 single crystal microwires (MWs). An ultrahigh photo-to-dark current (I photo/I dark) ratio ∼107 of the PDs has been realized. Compared with In/β-Ga2O3/In metal-semiconductor-mental (MSM) PD, the device with ITO as the interlayers between In and β-Ga2O3 show excellent performances, such as the high responsivity of 1720.2 A W−1 and 438.8 A W−1 under 260 nm illumination with reverse and forward bias, respectively. In addition, the device exhibited a very low dark current as low as 2.0 × 10−13 A and a photocurrent up to 1.0 × 10−6 A at the bias of −6 V (under 1.95 mW cm−1@260 nm). The rise and fall time of the device were 0.5 s and 0.2 s, which was significantly faster than MSM structure. Moreover, the device exhibited an ultrahigh solar-blind/visible rejection ratio (R 260 nm/R 400 nm) of 1.09 × 105, a detectivity D* of 1.23 × 1014 Jones and the external quantum efficiency of 4180.3%. The excellent performances of the PDs are attributed to the improved carrier separating process at the ITO/β-Ga2O3 interfaces and the reduced carrier trapping behavior induced by the β-Ga2O3 surface states. The introduction of ITO between MWs and the electrodes is of great significance for the application of β-Ga2O3 based detectors.

Ultrasensitive fully transparent amorphous Ga2O3 solar-blind deep-ultraviolet photodetector for corona discharge detection

Solar-blind deep-ultraviolet photodetectors are one of the most effective tools to detect corona discharge because high-voltage corona discharge is always accompanied by deep-ultraviolet light (UVC, 200–280 nm), referred to as solar-blind signals. In this study, a fully transparent metal-semiconductor-metal solar-blind photodetector with Al-doped ZnO (AZO) transparent electrodes was successfully constructed based on amorphous Ga2O3 film (a-Ga2O3) and prepared by radio frequency magnetron sputtering. The as-fabricated fully transparent device exhibits excellent performance, including an ultra-low dark current of 2.84 pA, a high photo-to-dark current ratio of 1.41 × 107, superb rejection ratio (R254/R400 = 2.93 × 105), a large responsivity of 2.66 A W−1, superb detectivity (4.84 × 1014 Jones), and fast response speed (rise/fall time: 24 μs/1.24 ms). It is worth noting that the fully transparent a-Ga2O3 photodetector demonstrates ultra-high sensitivity to weak solar-blind signals, far below the 100 nW cm−2 threshold of the test equipment. It also has high-resolution detection capabilities for subtle changes in radiation intensity. Acting as a sensor for the high-voltage corona discharge simulation detection system, the fully transparent a-Ga2O3 photodetector can clearly detect extremely weak solar-blind signals. The results described in this work serve as proof-of-concept for future applications of amorphous Ga2O3 solar-blind deep-ultraviolet photodetectors in high-voltage corona discharge detection.

High-performance β-Ga2O3-based solar-blind photodetector with ultralow dark current and fast photoresponse for deep-ultraviolet communication

Solar-blind deep-ultraviolet communication (SDUC) presents a promising candidate for use in short-range military communications. Solar-blind photodetectors (PDs) form up the core component of the SDUC system’s receiving signal. In this study, an easy-to-integrate metal-semiconductor-metal (MSM)-type solar-blind PD is successfully fabricated based on the β-Ga2O3 film deposited on c-plane sapphire substrates by low-cost radio-frequency magnetron sputtering. The fabricated device exhibits a high responsivity of 1.93 A W−1, a remarkable detectivity of 6.53×1013 Jones, and a considerable photo-to-dark current ratio of 3.58×105. Most importantly, the device shows an extremely low dark current of 82 fA and an ultrafast response speed of 11/240 µs; one of the most ultra-high performances ever reported for β-Ga2O3 solar-blind PDs. In addition, it is the first time that a high-performance β-Ga2O3-based PD that is integrated into a self-made SDUC system as a signal receiver is demonstrated to transmit ASCII codes with such high accuracy and a data rate of 10 kbps. The results reported in this work serve as proof-of-concept for future applications of β-Ga2O3 solar-blind deep-ultraviolet photodetectors in secure communications.

Fully transparent InZnSnO/β-Ga2O3/InSnO solar-blind photodetectors with high schottky barrier height and low-defect interfaces

Ultra-wide bandgap β-Ga2O3 photodiodes have received great attention due to transparent solar-blind deep ultraviolet photodetectors. We demonstrated an all oxide-based single-crystal β-Ga2O3 photodiode incorporated with transparent conductive InZnSnO and InSnO as Schottky and Ohmic contacts, respectively. High work function and low resistivity of InZnSnO allow for clear rectifying characteristics with a low dark current (<0.1 nA) of up to −100 V of reverse bias. The Schottky barrier height and junction defects at the Schottky interface were modified using post-annealing treatment, thereby influencing the deep ultraviolet photoresponse. The responsivity of the annealed device was 9.6 mA/W, decreasing the Schottky barrier height engineering, while the photo responding speed was degraded and caused a persistent photocurrent effect due to the generation of defect states.

Highly sensitive solar-blind deep ultraviolet photodetector based on graphene/PtSe2/β-Ga2O3 2D/3D Schottky junction with ultrafast speed

There is an emerging need for high-sensitivity solar-blind deep ultraviolet (DUV) photodetectors with an ultra-fast response speed. Although nanoscale devices based on Ga2O3 nanostructures have been developed, their practical applications are greatly limited by their slow response speed as well as low specific detectivity. Here, the successful fabrication of two-/three-dimensional (2D/3D) graphene (Gr)/PtSe2/β-Ga2O3 Schottky junction devices for high-sensitivity solar-blind DUV photodetectors is demonstrated. Benefitting from the high-quality 2D/3D Schottky junction, the vertically stacked structure, and the superior-quality transparent graphene electrode for effective carrier collection, the photodetector is highly sensitive to DUV light illumination and achieves a high responsivity of 76.2 mA/W, a large on/off current ratio of ~ 105, along with an ultra-high ultraviolet (UV)/visible rejection ratio of 1.8 × 104. More importantly, it has an ultra-fast response time of 12 µs and a remarkable specific detectivity of ~ 1013 Jones. Finally, an excellent DUV imaging capability has been identified based on the Gr/PtSe2/β-Ga2O3 Schottky junction photodetector, demonstrating its great potential application in DUV imaging systems.

Position-sensitive solar-blind deep-ultraviolet detectors

β-Ga2O3 is a direct ultra-wide bandgap semiconductor with an energy gap of 4.9 eV, which can serve as the ideal candidate for solar-blind deep-ultraviolet (DUV) detection. Despite the extensive research in Ga2O3 detectors, the positive sensitive ones have not been reported yet. Recently, researchers demonstrated the position sensitive solar-blind DUV photodetector by using the β-Ga2O3 thin film as an active layer. The photodetectors have high uniformity, fast response, and high DUV/visible rejection ratio. The DUV detector was successfully utilized to align the light beam. This work favors the applications of β-Ga2O3 in DUV or X-ray beam alignment or imaging.

Flexible transparent solar blind ultraviolet photodetector based on amorphous Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; grown on mica substrate

Solar-blind deep-ultraviolet (UV) photodetectors (PDs) based on the super-wide bandgap semiconductor material Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; is one of the hot topics of current research, but how to prepare high-performance Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-based solar-blind PDs in the field of flexible and transparent optoelectronics still faces challenges. In this work, an amorphous Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; film with high transmittance is grown on a flexible mica substrate by using the radio frequency magnetron sputtering technology. On this basis, using AZO as an electrode material, a transparent metal-semiconductor-metal (MSM) structured solar-blind deep ultraviolet photodetector based amorphous Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; film is fabricated, and the performance of PD in the planar state and after multiple bending are systematically compared and analyzed. The results show that the amorphous Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; based transparent PD has ultra-high visible light transparency and shows good solar-blind ultraviolet photoelectric characteristics. The responsivity of the PD under 254 nm light is 2.69 A/W, and the response time and the recovery time are 0.14 s and 0.31 s, respectively. After bending 300 times, the PD has a photoresponse behavior similar to its planar state, and the performance of the PD has no obvious attenuation phenomenon, showing good flexibility and stability. This work proves that AZO can be used as the electrode material of the next generation of flexible and visible light transparent Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; based photodetectors, and provides a reference for developing the high-performance flexible and transparent solar-blind deep ultraviolet photodetectors.

In situ and tunable structuring of semiconductor-in-glass transparent composite.

SummarySemiconductor-in-glass composites are an exciting class of photonic materials for various fundamental applications. The significant challenge is the scalable elaboration of composite with the desirable combination of tunable structure, high semiconductor loading ratio, and excellent transparency. Here we report that the topological engineering strategy via hybridization of the glass network former enables to surmount the aforementioned challenge. It not only facilitates the in situ precipitation of (Ga2-xAlx)O3 domains with continuously tunable composition but also allows to simultaneously refine the grain size and enhance the crystallinity. In addition, the composites exhibit excellent transparency and can host various active dopants. We demonstrate the attractive broadband optical response of the composite and achieve the pulse laser operation in mid-infrared waveband. The findings are expected to provide a fundamental principle of in situ modification in hybrid system for generation of high-performance semiconductor-in-glass composites.

Patterned growth of β-Ga2O3 thin films for solar-blind deep-ultraviolet photodetectors array and optical imaging application

Solar-blind deep-ultraviolet (DUV) photodetectors based on Ga2O3 have attracted great attention due to their potential applications for many military and civil purposes. However, the development of device integration for optoelectronic system applications remains a huge challenge. Herein, we report a facile method for patterned-growth of high-quality β-Ga2O3 thin films, which are assembled into a photodetectors array comprising 8 × 8 device units. A representative detector exhibits outstanding photoresponse performance, in terms of an ultra-low dark current of ∼0.62 pA, a large Ilight/Idark ratio exceeding 104, a high responsivity of ∼0.72 A W−1 and a decent specific detectivity of ∼4.18 × 1011 Jones, upon 265 nm DUV illumination. What is more, the DUV/visible (250/400 nm) rejection ratio is as high as 103 with a sharp response cut-off wavelength at ∼280 nm. Further optoelectronic analysis reveals that the photodetectors array has good uniformity and repeatability, endowing it the capability to serve as a reliable DUV light image sensor with a decent spatial resolution. These results suggest that the proposed technique offers an effective avenue for patterned growth of β-Ga2O3 thin films for multifunctional DUV optoelectronic applications.

Nanolayered Graphene/Hexagonal Boron Nitride/n-AlGaN Heterostructures as Solar-Blind Deep-Ultraviolet Photodetectors

The spectral specificity of deep-ultraviolet (UV) photodetectors makes them useful in many fields, spanning from disinfection of various surfaces and water purification to optical communication. As...

Solar-blind deep-ultraviolet photodetectors based on solution-synthesized quasi-2D Te nanosheets

Abstract Solar-blind deep ultraviolet (DUV) photodetectors with high responsivity (R) and fast response speed are crucial for practical applications in astrophysical analysis, environmental pollution monitoring, and communication. Recently, 2D tellurium has emerged as a potential optoelectronic material because of its excellent photoelectric properties. In this study, solar-blind DUV photodetectors are demonstrated based on solution-synthesized and air-stable quasi-2D Te nanosheets (Te NSs). An R of 6.5 × 104 A/W at 261 nm and an external quantum efficiency (EQE) of higher than 2.26 × 106% were obtained, which are highest among most other 2D material-based solar-blind DUV photodetectors. Moreover, the photoelectric performance of the quasi-2D Te-based photodetector exhibited good stability even after ambient exposure for 90 days without any encapsulation. These results indicate that quasi-2D Te NSs provide a viable approach for developing solar-blind DUV photodetectors with ultrahigh R and EQE.

Ultrathin Polymer Nanofibrils for Solar-Blind Deep Ultraviolet Light Photodetectors Application.

Solar-blind deep ultraviolet photodetectors (DUVPDs) based on conventional inorganic ultrawide bandgap semiconductors (UWBS) have shown promising application in various civil and military fields and yet they can hardly be used in wearable optoelectronic devices and systems for lack of mechanical flexibility. In this study, we report a non-UWBS solar-blind DUVPD by designing ultrathin polymer nanofibrils with a virtual ultrawide bandgap, which was obtained by grafting P3HT with PHA via a polymerization process. Optoelectronic analysis reveals that the P3HT-b-PHA nanofibrils are sensitive to DUV light with a wavelength of 254 nm but are virtually blind to both 365 nm and other visible light illuminations. The responsivity is 120 A/W with an external quantum efficiency of up to 49700%, implying a large photoconductive gain in the photoresponse process. The observed solar-blind DUV photoresponse is associated with the resonant mode due to the leakage mode of the ultrathin polymer nanofibrils. Moreover, a flexible image sensor composed of 10 × 10 pixels can also be fabricated to illustrate their capability for image sensing application. These results signify that the present ultrathin P3HT-b-PHA nanofibrils are promising building blocks for assembly of low-cost, flexible, and high-performance solar-blind DUVPDs.

Solar-Blind Self-Powered Photodetector Using Solution-Processed Amorphous Core–Shell Gallium Oxide Nanoparticles

Solution-processed deep ultraviolet (DUV) photodetectors based on wide band gap oxide semiconductors (WBGS) working in the <280 nm wavelength range are drawing increasing attention of the research community because of their cost-effective production and potential use in diverse applications. Here, we report on the synthesis of novel core-shell amorphous gallium oxide nanoparticles (NPs) (a-Ga2Ox/GaOx NPs) that have not been previously obtained. The amorphous gallium oxide NPs were synthesized from gallium nitride using the femtosecond laser ablation in liquid technique. Transmission electron microscopy and electron energy-loss spectroscopy measurements revealed the amorphous NP nature with a Ga-rich core and oxide-rich shell. Optical properties of these core-shell amorphous gallium oxide NPs were investigated by time-resolved spectroscopy and photoluminescence. As a proof of concept, the amorphous gallium oxide NPs were used as an active layer in a solar-blind DUV photodetector with high responsivity (778 mA/W) at 244 nm, which is the highest responsivity recorded to date for any solution-processed DUV photodetector. This work on a high-performance solution-processed device paves the way for large-scale industrial application of the WBGS.

Solution-processed solar-blind deep ultraviolet photodetectors based on strongly quantum confined ZnS quantum dots

Strongly quantum confined ZnS quantum dots were synthesized and solar-blind deep ultraviolet photodetectors were fabricated via a solution process.

Vertical metal-semiconductor-metal deep UV photodetectors based on hexagonal boron nitride nanosheets prepared by laser plasma deposition

We report on the synthesis and characterization of hexagonal boron nitride nanosheets (BNNSs) for deep ultraviolet (DUV) photodetector applications. The vertical structure metal-semiconductor-metal (MSM) solar-blind DUV photodetector based on BNNSs has been fabricated and tested. The detector performance is stable under UV radiation at temperatures exceeding 100°C. The bandgap engineered material has a cutoff wavelength of approximately 250 nm and does not respond to any longer wavelength or visible light. The photodetector demonstrates the advantages of hexagonal BNNSs as a wide band gap material for DUV detection in harsh environments.

β-Ga2O3 solar-blind deep-ultraviolet photodetector based on a four-terminal structure with or without Zener diodes

A four-terminal photodetector was fabricated on the (2¯01)-dominant β-Ga2O3 thin film which was deposited in a plasma-assisted molecular beam epitaxy system. The suitability of this film for solar-blind DUV detection was proved by its transmission spectra. Moreover, the device operating in a specific voltage-current mode can accurately detect the DUV radiation both qualitatively and quantitatively. Accordingly, a dark/photo voltage ratio of 15 was achieved, which is comparable to that of previously-reported β-Ga2O3 interdigital metal-semiconductor-metal photoconductor. More importantly, the aperture ratio of our proposed device exceeds 80%, nearly doubling that of the conventional interdigital metal-semiconductor-metal devices including photoconductor and Schottky-type photodiode, which can intensively benefit the detection efficiency. Furthermore, it was found the dark/photo voltage ratio was nearly trebled with the assistance of two Zener diodes, and further enhancement can be expected by increasing the operating current and/or adopting Zener diodes with smaller Zener voltage. Therefore, this work provides a promising alternative for solar-blind DUV detection.