Solar-blind UV Photodetectors Research Articles

Enhanced Performance of Self-Powered Solar-Blind Deep UV Photodetectors Based on ZnGa2O4/Ga2O3 Heterojunctions

Enhanced Performance of Self-Powered Solar-Blind Deep UV Photodetectors Based on ZnGa₂O₄/Ga₂O₃ Heterojunctions

High-performance Ga2O3 solar-blind UV photodetectors via film growth regulation and surface state engineering

Gallium oxide (Ga2O3) with a wide bandgap is emerging as one of the most promising candidates for solar-blind photodetectors (SBPDs). However, the practical application of Ga2O3-based SBPDs is impeded by substantial defects-related leakage currents, sluggish response speed, and high-cost, making their practical applications face great challenges. Here, we proposed strategic films growth regulation and surface state engineering to grow high-quality yet economical β-Ga2O3 films, thereby achieving high-performance SBPDs. High-resolution transmission electron microscopy revealed the presence of high-quality films with an extremely regular arrangement of β-Ga2O3 (2‾01) planes. The full width at half maximum and root mean square roughness values are 0.07° and 0.716 nm, respectively. The β-Ga2O3 films demonstrated a significant reduction in VO concentrations after O2/N2 plasma treatment. This process can effectively minimize thermal damage to the sample surface while retaining highly reactive free radicals. The photocurrents of devices can be further enhanced, leading to a larger PDCRs of 8.6 × 107, through N2 plasma treatment. Moreover, the films effectually suppress the persistent photoconductivity effect with τr and τd values of 5.31/0.97 s and 0.49/0.87 s before and after N2 plasma treatment, respectively. We have demonstrated the influence mechanism of O2/N2 plasma treatment on photoelectronic performance. This study provides a practical approach to growing high-quality β-Ga2O3 films and preparing high-performance but low-cost Ga2O3-based SBPDs.

Fabrication of Al doped α-GaOOH nanorod arrays on FTO for self-powered photoelectrochemical solar-blind UV photodetectors

Al doped α-GaOOH nanorod arrays were grown on FTO via hydrothermal processes by using gallium nitrate and aluminum nitrate mixed aqueous solutions with fixed 1:1 mole ratio as precursors. With increasing the gallium nitrate precursor concentrations, the Ga/Al atom ratios in nanorod arrays increase from 0.36 to 2.08, and the length becomes much longer from 650 nm to 1.04 μm. According to the binding energy difference between Ga 2p3/2 core level and its background in x-ray photoelectron spectroscopy, the bandgap is estimated to be around 5.3 ± 0.2 eV. Al doped α-GaOOH nanorod array/FTO photoelectrochemical photodetectors show enhanced self-powered solar-blind UV photodetection properties, with the decrease of Ga precursor concentrations. The maximum responsivity at 255 nm is 0.09 mA W−1, and the fastest response time can reach 0.05 s. The improved photoresponse speed is ascribed from much shorter transportation route, accelerated carrier recombination by recombination centers, and smaller charge transfer resistance at the α-GaOOH/electrolyte interface with decreasing the gallium nitrate precursor concentrations. The stability and responsivity should be further improved. Nevertheless, this work firstly demonstrates the realization of self-powered solar-blind UV photodetection for α-GaOOH nanorod arrays on FTO via Al doping.

Reduction of oxygen vacancies in Mg–N codoped Ga2O3 films for improving solar-blind UV photodetectors performance

Solar-blind photodetectors based on gallium oxide (Ga2O3) have shown possibilities in optical imaging, spatial communication, and other fields. The high oxygen vacancy (VO) content inherent in Ga2O3 film would inevitably result in poor photoelectric detection capability. This work suggests using a codoping for reducing VO concentrations in Ga2O3 films. In a N2O atmosphere, magnesium and nitrogen codoped gallium oxide (Mg–N:Ga2O3) films were grown using the pulsed laser deposition (PLD) technique on (0001) sapphire substrates. It is possible to produce codoped Ga2O3 thin films with low oxygen vacancy density and high crystalline quality by thoroughly examining and optimizing preparation conditions. Metal-semiconductor-metal (MSM) photodetectors were constructed using both pristine and Mg–N codoped Ga2O3 thin films as the active layer. The photodetector with a codoped active layer outperforms those with pristine Ga2O3, with a quick decay time of 20 ms, a high sensitivity of 2.61 × 105, and a high responsivity of 0.191 A/W under 254 nm UV light irradiation, highlighting the significance of the VO concentration decrease in the application of Ga2O3-based solar-blind photodetectors.

Influence of annealing pretreatment in different atmospheres on crystallization quality and UV photosensitivity of gallium oxide films.

Due to their high wavelength selectivity and strong anti-interference capability, solar-blind UV photodetectors hold broad and important application prospects in fields like flame detection, missile warnings, and secure communication. Research on solar-blind UV detectors for amorphous Ga2O3 is still in its early stages. The presence of intrinsic defects related to oxygen vacancies significantly affects the photodetection performance of amorphous Ga2O3 materials. This paper focuses on growing high quality amorphous Ga2O3 films on silicon substrates through atomic layer deposition. The study investigates the impact of annealing atmospheres on Ga2O3 films and designs a blind UV detector for Ga2O3. Characterization techniques including atomic force microscopy (AFM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) are used for Ga2O3 film analysis. Ga2O3 films exhibit a clear transition from amorphous to polycrystalline after annealing, accompanied by a decrease in oxygen vacancy concentration from 21.26% to 6.54%. As a result, the response time of the annealed detector reduces from 9.32 s to 0.47 s at an external bias of 10 V. This work demonstrates that an appropriate annealing process can yield high-quality Ga2O3 films, and holds potential for advancing high-performance solar blind photodetector (SBPD) development.

Flexible and Self-Powered Solar-Blind UV Photodetector Based on the Ti/α-Ga2O3/Electrolyte Heterojunction with High Stability

Flexible and Self-Powered Solar-Blind UV Photodetector Based on the Ti/α-Ga₂O₃/Electrolyte Heterojunction with High Stability

Under-Seawater Immersion β-Ga2O3 Solar-Blind Ultraviolet Imaging Photodetector with High Photo-to-Dark Current Ratio and Fast Response.

This work displays a photovoltaic solar-blind UV photodetector based on a β-Ga2O3 photoelectrode/simulated seawater (NaCl). The photodetector exhibits extremely high photocurrent (6.70 μA); the responsivity can reach 23.47 mA W-1, and the fastest response rise time is 40 ms under 213 nm illumination at zero bias, the responsivity is 25.10 mA W-1 at 0.8 V, and the photo-to-dark current ratio reaches a maximum of 4663, whose responsivity can be effectively adjusted by changing electrolyte concentration, ensuring a good working stability of this device. In addition, with original seawater as the electrolyte, the detector still achieves a high switching ratio (754) and stable detection under zero bias, demonstrating its capability for practical uses. What's more, we present the capability of the photodetector in seawater imaging. This work provides a method for solar-blind UV detection in seawater, which compensates for the limited detection of most current seawater detectors in the visible band, and can provide certain guidance in the field of seawater detection.

Study on PECVD-hetero-grown β-Ga2O3 thin film and temperature-modulated solar-blind UV photodetection

Using a convenient and low-cost plasma-enhanced chemical vapor deposition technique, uniform Ga2O3 thin films were hetero-grown on c-plane sapphire substrates at different temperatures, with a root mean square roughness as low as 2.71 nm and a growth rate of up to 1121.30 nm h−1; and then the solar-blind UV photodetection performances were discussed in detail. Metal-semiconductor-metal solar-blind UV photodetectors (PDs) based on the five Ga2O3 films prepared at different temperatures exhibit ultra-low dark currents (I dark) ranging among 22–168 fA. Under the illumination of 254 nm UV light, the PD prepared by the film grown at 820 °C possesses the highest performance, with a high photo-to-dark current ratio of 1.47 × 105, a low rise/decay time of 0.067/0.13 s, a specific detectivity (D *) of 3.56 × 1012 Jones, and a linear dynamic range of 92.89 dB. Overall, the results in this work may well provide a referable method for growing cost-effective and ultralow-noise Ga2O3 thin films, as well as achieving decent solar-blind UV sensing applications.

Study of self-powered UV detector based on Sb-doped β-Ga2O3 thin film/P–Si heterojunction

Sb-doped β-Ga2O3 thin films with different contents were grown on p-type Si substrates by chemical vapor deposition (CVD). It is found that the surface morphology and crystal quality of β-Ga2O3 films are improved with increasing Sb contents, which is mainly caused by the fact that amount of Sb can act as surface activator. The self-powered solar-blind UV photodetectors base on Sb-doped β-Ga2O3 thin films/Si heterojunction was fabricated. The heterojunction device exhibited high Ilight/Idark ratio of up to ∼1.6 × 103 and relatively fast photoresponse speed (0.07/0.09 s). Furthermore, the heterojunction photodetectors also show excellent photosensitive characteristics with responsivity of 210 mA/W, and external quantum efficiency of 103% under 254 nm illumination (60 μW/cm2) at 0 V. This doping technique provided a feasible method for n-type β-Ga2O3 doping and the preparation of ultraviolet photodetectors.

Semiconductor applications of Yb2O3: Constructing heterojunction solar-blind UV photodetectors with graphene

Exploring the semiconductor materials with suitable gap and chemical stability is the key to developing solar-blind ultraviolet photodetectors with high stability, responsivity, and detectivity. However, available materials are limited currently, hindering the development of solar-blind detectors greatly. Rare earth oxides (Yb2O3) have the bandgap and high-dielectric constants suitable for solar-blind detection, but its potential of being applied to broadband gap semiconductors has not been deeply studied. Therefore, to activate the semiconductor characteristics of Yb2O3, this work builds a p-Gr/i-Yb2O3/n-Si heterojunction solar-blind ultraviolet photodetector by introducing single-layer graphene. Through tests, this device has an absorption cutoff wavelength of 271 nm, which can almost cover the entire solar-blind ultraviolet band, and a high responsivity of 9.78 mA/W under 0 V bias with the rise and fall time as short as 87 and 73 ms, respectively. This work not only prepares a high-performance solar-blind UV photodetector but also presents the potential application of Yb2O3 in the solar-blind ultraviolet light detection. The high-dielectric performance of rare earth oxides makes it expected to be used for the photoelectric chip unit in future integrated circuit.

Comprehensive Study on Ultra-Wide Band Gap La2O3/ε-Ga2O3 p-n Heterojunction Self-Powered Deep-UV Photodiodes for Flame Sensing.

Solar-blind UV photodetectors have outstanding reliability and sensitivity in flame detection without interference from other signals and response quickly. Herein, we fabricated a solar-blind UV photodetector based on a La2O3/ε-Ga2O3 p-n heterojunction with a typical type-II band alignment. Benefiting from the photovoltaic effect formed by the space charge region across the junction interface, the photodetector exhibited a self-powered photocurrent of 1.4 nA at zero bias. Besides, this photodetector demonstrated excellent photo-to-dark current ratio of 2.68 × 104 under 254 nm UV light illumination and at a bias of 5 V, and a high specific detectivity of 2.31 × 1011 Jones and large responsivity of 1.67 mA/W were achieved. Importantly, the La2O3/ε-Ga2O3 heterojunction photodetector can rapidly respond to flames in milliseconds without any applied biases. Based on the performances described above, this novel La2O3/ε-Ga2O3 heterojunction is expected to be a candidate for future energy-efficient fire detection.

Solar-blind UV communication based on sensitive β -Ga2O3 photoconductive detector array

In this work, a solar-blind UV photodetector array is fabricated and discussed, based on a metalorganic chemical vapor deposition-grown β-Ga2O3 thin film, toward optical communication application. The high-performance photodetector unit shows a significant photo-to-dark current ratio of 3.4 × 105, a high responsivity of 61.3 A/W, an external quantum efficiency of 3 × 104%, a specific detectivity of 5.2 × 1014 Jones, and a fast response time of 35 ms. In addition, a solar-blind UV/visible light rejection ratio of 2.43 × 102 is achieved, suggesting decent spectral selectivity. For the array, the maximum photocurrent standard deviation is below 12% for every group with a similar layout arrangement. Furthermore, the dark current is at picoampere level, leading to low background noise for the optical communication system. Taking the 50% photocurrent value as the readout threshold line to avoid interference from the exterior meanwhile retaining about 500 on/off cycles, the optical communicated result shows effective outputting information “NJUPT2023” coming from a total of 256 “1” and “0” signals.

High-detectivity solar-blind deep UV photodetectors based on cubic/monoclinic mixed-phase (InxGa1−x)2O3 thin films

Mixed-phase (InxGa1−x)2O3 films were fabricated by excessive doping of In in Ga2O3 and by controlling different precursor weight ratios of monoclinic Ga2O3 and cubic In2O3. X-ray diffraction and transmission spectra showed that excessive indium doping over the solubility of In in Ga2O3 causes phase separation and the formation of films in which monoclinic (InxGa1−x)2O3 (β-IGO) and cubic (InxGa1−x)2O3 (c-IGO) coexist. The (InxGa1−x)2O3 photodetector with a ratio of Ga2O3: In2O3 = 10: 1 is highly sensitive to solar-blind radiation with an ultralow dark current of 0.03 pA and a large I254 nm/Idark up to 2.53 × 107 under − 7 V bias. Under a bias of 10 V, the device has a high responsivity and detectivity of 0.97 A/W and 4.62 × 1014 Jones, respectively. The ultralow dark current is attributed to the interface states at the grain boundaries between β-IGO and c-IGO in the mixed-phase films, which can trap electrons and form potential barriers that inhibit carrier transport. Irradiation under 254 nm light generates electron-hole pairs in β-IGO and c-IGO, which are separated by internal electric fields. The holes are captured during migration by potential traps, causing continuous electron injection and sweep-out until the holes escape from the traps, resulting in a device with good performance. The proposed alloying method could be used to fabricate future photoelectric devices.

Comprehensive enhancement of ZnGa2O4-based solar blind photodetector performance by suppressing defects in oxygen-rich atmosphere

ZnGa2O4 is a potential candidate material for next-generation solar-blind UV photodetectors (PDs) owing to its intrinsically wide bandgap and various favorable physical properties. The photoelectric properties of metal oxides are susceptible to oxygen. This study investigated the effect of oxygen flow on the properties of ZnGa2O4 thin films. Furthermore, photovoltaic devices with Au as Schottky contacts were fabricated to compare the performance. The ZnGa2O4 films grown in an oxygen-rich atmosphere exhibit better crystallinity and fewer oxygen vacancies than those grown in an oxygen-poor atmosphere, and the corresponding device demonstrates excellent performance parameter at a bias voltage of 10 V: a responsivity (R), external quantum efficiency (EQE) and detectivity (D*) up to 15.62 A/W, 7626%, ∼1015 Jones, respectively. Additionally, the suppression of oxygen vacancies prevents persistent photoconductivity under low light irradiation. The device possesses satisfactory rise/decay times of 0.125/0.025 s and maintains excellent stability and repeatability. Our study confirms that sputtering in an oxygen-rich atmosphere is an effective strategy for producing ZnGa2O4 thin films that can be applied for fabricating ZnGa2O4 solar-blind PDs with excellent comprehensive performance.

MgO (1 0 0) as an affordable support for heteroepitaxial growth of high-quality β-Ga2O3 thin films and related highly-sensitive solar-blind UV photodetectors

Heteroepitaxial growth of high-quality β-Ga2O3 thin films on foreign substrates is of crucial importance for achieving high-performance power-electronic and optoelectronic devices with affordable prices. Herein, we demonstrate realization of heteroepitaxial growth of high-quality β-Ga2O3 films on MgO(100) via pulsed laser deposition, and achievement of related highly-sensitive solar-blind ultraviolet photodetectors (SBUVPDs). Under optimized oxygen pressure (7 Pa), single-phase, (100)-oriented, and atomically-smooth β-Ga2O3 films were grown epitaxially on MgO(100), consisting of unique 8–12 nm-wide columnar nanodomains. Atomically-resolvable aberration-corrected transmission electron microscopy unveiled initial growth of a cubic γ-phase transition layer of ∼ 8 nm thickness, and directly visualized occurrence and preferable location of oxygen vacancies at domain walls in the further grown β-Ga2O3 film. Density-functional-theory simulations rationalized the formation of columnar nanodomains in terms of energetics, and presumably identified the nanodomains interface orientations as (112¯)/(11¯2¯). The heteroepitaxial β-Ga2O3(100)/MgO(100) film-based photodetector demonstrates excellent performance, featured with exceedingly-low dark current, remarkably-high light-to-dark current ratio, and ultrahigh responsivity and detectivity (Idark = 0.6 pA, Ilight/Idark = 1.47 × 107, R = 191 A/W, D*=3.08 × 1015 Jones) as well as fast response speed towards 255 nm-UV detection. This work highlights MgO(100) as a suited yet affordable foreign substrate for heteroepitaxial growth of high-quality β-Ga2O3 films towards further development of high-performance devices such as SBUVPDs.

Ion energy dependence of dry etch damage depth in Ga2O3 Schottky rectifiers

The β-polytype of Ga2O3 has a high critical electric field strength (∼8 MV.cm−1) and can be grown as large diameter (6 in.) single crystal boules by inexpensive melt-growth techniques. This makes it promising for next generation power electronics and solar-blind UV photodetectors. Since wet etching is not feasible for patterning such devices due to the chemical inertness of Ga2O3, attention is focused on dry etching, with the attendant issue of surface modification due to chemical or ion-induced changes. In this work, we demonstrate that dry etch damage in β-Ga2O3 is manifested by a reduction in near-surface carrier concentration, possibly due to the introduction of Gav acceptor states. The depth to which the carrier density is affected depends on the interplay between ion energy and etch rate, with faster etch rates reducing the depth of the remaining damaged region. The maximum damage depth observed experimentally from capacitance-voltage profiling on Schottky rectifiers was ∼ 110 nm, well beyond the range of the ions in the Inductively Coupled Plasmas and emphasizing that rapid diffusion of point defects occurs into the sample during the etch step. Using Schottky rectifier structures as a platform to understand the effect of dry etch damage on device parameters, we found that on-state resistance was more affected than ideality factor or breakdown voltage, with a large increase (5x) for ion energies ≥ 325 eV. Reverse current density characteristics showed the presence of trap-assisted space-charge-limited conduction in the damaged layers. The implications for high power rectifier fabrication are discussed.

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 .

Modeling and simulation of Ga2O3 thin film solar blind UV photodetector

In this work, 2D physical modeling and simulation of gallium oxide based thin film solar blind UV photodetector device using COMSOL multiphysics software is carried out. Doping profile, energy level diagram, responsivity and spontaneous emission analysis of the gallium oxide based thin film solar blind UV photodetector are analysed and reported. The p-i-n doped thin film Ga2O3 photodetector device with 5 μm width, 1 μm height exhibits a responsivity of 1.1 × 10−3 A/W, external quantum efficiency (EQE) of 70% at 2 V reverse voltage bias and the total emitted power of 7.41 × 1021 m−3s−1 at 4.9 eV photon energy. Metal contact analyses have been carried out using various elements, and Schottky contacts are established with gold, nickel and platinum metal contacts.

Self-powered solar-blind UV photodetectors based on Zn:NiO/p-Si heterojunction devices

Self-powered solar-blind UV photodetectors based on Zn:NiO/p-Si heterojunction devices

CVD Approach to a Single Gallium Oxide Nanowire for Solar-blind UV Detector

Aims: Finding a simple, energy-saving and low-cost synthesis method to process gallium oxide nanowires by CVD for solar-blind detector. Background: Due to a bandgap of 4.5 ~ 4.9 eV and a high breakdown field strength of 8 MV/cm, gallium oxide (Ga2O3) has great application prospects in solar blind ultraviolet detection and highpower devices. Notably, Ga2O3 NWs are currently the key research objects of solar-blind UV detection materials because of the characteristics of efficient photocarrier separation and collection, and the bandgap width perfectly matches the energy of deep ultraviolet photons. Objective: To find a simple method to synthesize Ga2O3 nanowire with smooth surface and uniform diameter, and the prepared single gallium oxide nanowire UV detector has high photoelectric conversion efficiency. Methods: Ga2O3 NWs are prepared on the SiO2/Si substrate by chemical vapor deposition (CVD) approach at low reaction temperature with gold particles serving as the catalyst and gallium arsenide (GaAs) as a gallium source. Results: X-ray diffraction and Raman spectroscopy characterization indicate the crystal structure of NWs is β-Ga2O3, and scanning electron microscope (SEM) characterization proves that the NWs have a uniform diameter and smooth surface. Moreover, the high-resolution transmission electron microscopy (HRTEM) characterization shows that the material had high crystal quality. Moreover, the photoconductive solar-blind UV detector with a single Ga2O3 NW is prepared, showing the excellent performance of the high responsivity and external quantum efficiency. Conclusion: The effects of growth temperature and the size of gold catalyst on the morphology of β-Ga2O3 NWs have been investigated. The results show that with the reaction temperature is 625 °C and the diameter of Au catalyst is about 30~50 nm, it is more conducive to the formation of NMs with crystal structure, smooth surface and uniform diameter. The performance of the solar-blind UV photodetector shows that the device has higher sensitivity (R = 149.82 A/W), external quantum efficiency (EQE = 73206%), and response rate τrise = 0.66 s, and τdown = 0.45 s.