Solar-blind Ultraviolet Photodetectors Research Articles

Photoelectrochemical properties of self-powered corundum-structured Ga2O3 nanorod array/fluorine-doped SnO2 photodetectors modulated by precursor concentrations

Herein, corundum-structured Ga2O3 (α-Ga2O3) nanorod array/fluorine-doped SnO2 (FTO) structures have been fabricated by hydrothermal and thermal annealing processes with different precursor concentrations from 0.01 to 0.06 M. The diameter and length of the nanorod arrays are much larger with increasing precursor concentrations due to more nucleation sites and precursor ions participating in the reaction procedures. The optical bandgap decreases from 4.75 to 4.47 eV because of the tensile stress relieving with increasing the precursor concentrations. Based on self-powered photoelectrochemical (PEC) photodetectors, the peak responsivity is improved from ∼0.33 mA W−1 for 0.06 M to ∼1.51 mA W−1 for 0.02 M. Schottky junctions can be formed in PEC cells. More photogenerated carriers can be produced in wider depletion region. From Mott–Schottky plots, the depletion regions become much wider with decreasing the precursor concentrations. Therefore, the enhance responsivity is owing to the wider depletion regions. Due to the reduced possibility of photogenerated holes captured by traps ascribed from fewer green and yellow luminescence defects, smaller charge transfer resistance, and shorter transportation route, the decay time becomes much faster through decreasing the precursor concentrations. Compared with the other self-powered α-Ga2O3-nanorod-array-based PEC photodetectors, it shows the fastest response time (decay time of 0.005 s/0.026 s) simply modulated by precursor concentrations for the first time without employing complex precursors, seed layers or special device designs. Compared with other high-responsivity monoclinic Ga2O3 (β-Ga2O3) self-powered photodetectors, our devices also show comparable response speed with simple control and design. This work provides the realization of fast-speed self-powered Ga2O3 based solar-blind ultraviolet photodetectors by simple modulation processes and design, which is a significant guidance for their applications in warnings, imaging, computing, communication and logic circuit, in the future.

Highly Wavelength-Selective Self-Powered Solar-Blind Ultraviolet Photodetector Based on Colloidal Aluminum Nitride Quantum Dots.

Colloidal quantum dots are semiconductor nanocrystals endowed with unique optoelectronic properties. A major challenge to the field is the lack of methods for synthesizing quantum dots exhibit strong photo-response in the deep-ultraviolet (DUV) band. Here, a facile solution-processed method is presented for synthesizing ultrawide bandgap aluminium nitride quantum dots (AlN QDs) showing distinguished UV-B photoluminescence. Combined with the strong optical response in solar blind band, a solution-processed, self-powered AlN-QDs/β-Ga2O3 solar-blind photodetector is demonstrated. The photodetector is characterized with a high responsivity of 1.6mAW-1 under 0V bias and specific detectivity 7.60 × 10-11 Jones under 5V bias voltage with good solar blind selectivity. Given the solution-processed capability of the devices and extraordinary properties of AlN QDs, this study anticipates the utilization of AlN QDs will open up unique opportunities for cost-effective industrial production of high-performance DUV optoelectronics for large-scale applications.

Heteroepitaxial growth of Ga2O3 thin films on nickel-nanodot-induced buffer layers for solar-blind ultraviolet photodetector applications

Heteroepitaxial growth of gallium oxide (Ga2O3) thin films has been conducted on nickel (Ni)-nanodot-induced buffer layers using a mist chemical vapor deposition. The separation degree and droplet size of the Ni nanodots on sapphire substrates were controlled through a thermal annealing process, thereby being used as templates for the Ga2O3 thin-film growth. The growth of the inverted cone-shaped ε-Ga2O3 polymorph was observed on the nanodots while the α-Ga2O3 polymorph was grown on the sapphire substrate without nanodots, ultimately a thin film with a mixture of ε and α polymorphs can be achieved. By comparing photoresponses of metal–semiconductor–metal photodetectors fabricated on the thin film with the mixed polymorphs and on a single-crystalline α-Ga2O3 film, a promising template for using solar-blind photo-detecting applications has been verified.

Wet Chemical Synthesis of Ultrathin γ-Ga2O3 Quantum Wires Enabling Far-UVC Photodetection with Ultrahigh Selectivity and Sensitivity.

As compared to solar-blind ultraviolet (UV) photodetectors (PDs), far-UVC PDs not only show some irreplaceable advantages but also are more challenging to be developed. To solve this challenge, we report herein a soft template-assisted solvothermal route to synthesize ultrathin γ-Ga2O3 quantum wires (UQWs) with diameters down to 1-2 nm. These UQWs all exhibit a cluster-like absorption feature with a strong peak located between 190 and 230 nm and an edge below 250 nm, allowing highly selective absorption to far-UVC light. Notably, their normalized absorption coefficients were experimentally and theoretically confirmed to increase obviously with decreasing their diameters. Self-powered photoelectrochemical-type PDs based on Ga2O3 QWs of 1.7 nm diameter were therefore fabricated, exhibiting an excellent far-UVC detection performance with an unprecedented ultrahigh spectral selectivity (R210 nm/R250 nm = 452). As a proof of concept, this paper offers a new idea for developing ultrawide bandgap semiconductor materials and devices by leveraging a strong quantum confinement effect.

Highly Sensitive Narrowband AlGaN Solar Blind Ultraviolet Photodetectors Using Polarization Induced Heterojunction Barrier

Highly Sensitive Narrowband AlGaN Solar Blind Ultraviolet Photodetectors Using Polarization Induced Heterojunction Barrier

Piezoelectricity Enhanced Self-Powered Solar-Blind Ultraviolet Photodetectors Based on Ga2O3/ZnO Heterojunction

Piezoelectricity Enhanced Self-Powered Solar-Blind Ultraviolet Photodetectors Based on Ga₂O₃/ZnO Heterojunction

Highly sensitive self-powered solar-blind ultraviolet photodetectors based on n-Zn1-xFexO/p-Si heterojunctions

The pristine and iron-doped ZnO thin films were fabricated on p-type silicon and glass substrates using the radio-frequency magnetron sputter deposition technique. The structural, morphological, and electrical properties of the deposited thin films were analyzed using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), and I-V characteristics. XRD analysis revealed the preferential growth of ZnO along the c-axis, with lattice parameter (c) values of 5.216, 5.234, and 5.241 Å for the pristine ZnO, Zn0.97Fe0.03O, and Zn0.95Fe0.05O thin films, respectively. The crystallite sizes were measured to be 13.2 nm, 16.2 nm, and 18.3 nm for the respective films. The elemental analysis of the deposited films was done under X-ray photoelectron spectroscopy (XPS), which revealed the concentrations of iron Zn0.97Fe0.03O, and Zn0.95Fe0.05O thin films were 2.93 at% and 5.14 at%, respectively. Raman spectroscopy confirmed the presence of the hexagonal wurtzite structural form in the deposited films. The I-V characteristics of the deposited films confirmed the formation of a heterojunction between the film and the silicon substrate. Furthermore, the constructed heterojunction devices were evaluated for their ability to detect ultraviolet (UV) radiations of wavelengths 365 nm and 254 nm. The devices exhibited response and recovery times of less than 1 s. The detectivity values were found to be 0.321 ×1011, 1.051 ×1011, and 2.992 ×1011 Jones for the ZnO/p-Si, Zn0.97Fe0.03O/p-Si, and Zn0.95Fe0.05O/p-Si devices, respectively, under a fixed illumination intensity of 0.812 mW/cm2 for a UVA source with a wavelength of 365 nm. These results confirm the excellent photodetection ability of the constructed devices. The mechanism of UV radiation detection by the devices has also been extensively discussed.

Phase Transition and Bandgap Engineering of MgSnO Thin Films for Solar-Blind Ultraviolet Photodetector Applications

Phase Transition and Bandgap Engineering of MgSnO Thin Films for Solar-Blind Ultraviolet Photodetector Applications

Self-powered solar blind ultraviolet photodetector based on amorphous (In0.23Ga0.77)2O3/bixbyite (In0.67Ga0.33)2O3 heterojunction

Self-powered solar-blind ultraviolet photodetectors are considered for potential applications in secure communication and space detection. However, high-quality p-type wide bandgap semiconductors are nonexistent due to the self-compensation effect, which makes the design of p-n homojunction photodetectors a challenging proposition to date. In this work, a self-powered solar-blind ultraviolet photodetector is fabricated and discussed, based on a novel heterojunction of (InxGa1−x)2O3 ternary alloy films with two different compositions, which has a flexible design and can be easily fabricated for different applications. The heterojunction consists of an amorphous (In0.23Ga0.77)2O3 on the top of a bixbyite (In0.67Ga0.33)2O3 film prepared by radio frequency magnetron sputtering. The amorphous (In0.23Ga0.77)2O3/bixbyite (In0.67Ga0.33)2O3 heterojunction photodetector exhibits a responsivity of 5.78 mA/W, a detectivity of 1.69 × 1011 cm Hz1/2 W−1, and a high solar-blind UV (248 nm)/visible light (450 nm) rejection ratio of 1.39 × 103 at zero bias, suggesting decent spectral selectivity and high performance. The responsivity and peak wavelength of this photodetector can be tuned by the film thickness of the amorphous (In0.23Ga0.77)2O3. This work provides a new design for self-powered solar-blind UV detectors based on ternary alloy heterojunctions.

Solar-blind ultraviolet photodetector based on Nb2C/β-Ga2O3 heterojunction

β-Ga2O3 has been widely investigated for its stability and thermochemical properties. However, the preparation of β-Ga2O3 thin films requires complex growth techniques and high growth temperatures, and this has hindered the application of β-Ga2O3 thin films. In this study, β-Ga2O3 thin films with good crystalline quality were prepared using a green method, and an ultraviolet (UV) detector based on β-Ga2O3 with a photocurrent of 2.54 × 10–6 A and a dark current of 1.19 × 10–8 A has been developed. Two-dimensional materials have become premium materials for applications in optoelectronic devices due to their high conductivity. Here, we use the suitable energy band structure between Nb2C and Ga2O3 to create a high carrier migration barrier, which reduces the dark current of the device by an order of magnitude. In addition, the device exhibits solar-blind detection, high responsiveness (28 A W−1) and good stability. Thus, the Nb2C/β-Ga2O3 heterojunction is expected to be one of the promising devices in the field of UV photoelectric detection.

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.

Enhanced Responsivity of Solar Blind Ultraviolet Photodetector by PEALD Deposited Zn-Doped Ga2O3 Thin Films

Enhanced Responsivity of Solar Blind Ultraviolet Photodetector by PEALD Deposited Zn-Doped Ga₂O₃ Thin Films

Ultrafast self-powered solar-blind ultraviolet photodetector based on Ga2O3 microwire/GaN p-n heterojunction using a single-layer graphene as electrode

Ultrafast self-powered solar-blind ultraviolet photodetector based on Ga₂O₃ microwire/GaN p-n heterojunction using a single-layer graphene as electrode

Self-powered AlGaN-based MSM solar-blind ultraviolet photodetectors with high Al-content AlxGa1−xN/AlyGa1−yN asymmetrical heterostructure

An Al0.4Ga0.6N-based metal–semiconductor–metal (MSM) ultraviolet (UV) photodetector (PD) based on intentionally asymmetrical polarized Al0.55Ga0.45N/Al0.4Ga0.6N/Al0.65Ga0.35N heterostructure has been fabricated and investigated, which achieves the self-powered capabilities. Operated at zero bias, the device presents an ultralow dark current of 7.8 × 10−13 A, a high peak responsivity of 0.04 A/W at ∼275 nm, a cut-off wavelength at ∼285 nm, and a corresponding detectivity of 3.1 × 1012 Jones. In comparison, the device with symmetrical heterostructure has no response at 0 V, confirming the effect of the proposed asymmetrical MSM structure. Furthermore, it is expressly demonstrated that the structure provides an asymmetrical energy band due to different barrier heights at the metal/Al0.4Ga0.6N and metal/Al0.55Ga0.45N/Al0.4Ga0.6N Schottky contacts and enhances the built-in electric field in the Al0.4Ga0.6N active layer owing to its polarization effect through simulations theoretically. Therefore, the improvement of photogenerated carrier transport can be obtained at 0 V, contributing to the high-performance self-powered UV PD.

Study of [formula omitted]-Ga[formula omitted]O[formula omitted](001)/sapphire (a-plane) heterostructure in wide bandgap solar-blind deep-ultraviolet photodetector

Gallium oxide (Ga2O3) with ultra-wide band gap and high radiation resistance have great potential in solar-blind ultraviolet (UV) photodetectors, but its development is limited by expensive Ga2O3 substrate materials. Sapphire substrate, due to its high hardness, mature production process and low cost, has become one of the most favorable substrate materials for optoelectronic devices. So, Ga2O3-based optoelectronic devices on sapphire substrates hold significant commercial value. In this work, using first-principles density functional theory (DFT) calculations, we investigate the influence of interfacial oxygen concentration on the β-Ga2O3(001)/sapphire(112̄0) heterostructure. The results show that the bonding strength between O-terminated and Al-terminated interfaces is strong, indicating favorable thermodynamic stability of this heterostructure. Furthermore, we discover that the metal-O-metal bonding configuration at the interface effectively reduces the number of interfacial defects, increase the built-in electric field strength within the heterostructure, and improves the deposition quality of the β-Ga2O3 film. This work holds significant implications for the research on β-Ga2O3 solar-blind UV photodetectors based on sapphire substrates.

Pinhole-free CsCu2I3 thin films by I2-modification for solar-blind ultraviolet photodetector and application to free-space optical communication

Recently, copper-based lead-free perovskites have emerged as a promising material due to their unique physical properties, abundance on earth, and lower toxicity. Among them, CsCu2I3 has received extensive attention for optoelectronic device applications due to its excellent air stability and stable self-trapped exciton-based yellow emission. However, the inherent one-dimensional crystal structure of CsCu2I3-based perovskite makes it difficult to control the morphology during the synthesis process, which results in a high density of pinhole defects on the thin films. Here, we reported a strategy to obtain a high-quality and pinhole-free CsCu2I3 thin film by modifying growth kinetics by adding I2 during synthesis. The I2-modified CsCu2I3 film improved surface morphology while preserving crystalline and optical properties. Therefore, the ultraviolet (UV) photodetector based on the I2-modified CsCu2I3 film showed enhanced performances in the solar-blind waveband, including a high responsivity of 1.74 μA/W and fast response and recovery times of 0.684 and 0.686 s, respectively. Finally, the solar-blind UV photodetector based on the I2-modified CsCu2I3 thin film exhibited outstanding demonstration in optical communication systems without ambient interference, indicating its potential for various optoelectronic applications.

Solar-blind ultraviolet-visible dual-spectral photodetector based on carbon nanodots/flexible-silicon heterojunction

Flexible solar-blind ultraviolet (UV) photodetectors (PDs) have important applications in biomedical and wearable electronic devices. Herein, a dual-spectral carbon nanodots/flexible n-silicon heterojunction photodetector is reported that always shows a photo response in UV illumination, while in visible illumination there is a photo response only in forward bias. The working mechanism of the carbon nanodots/silicon heterojunction was investigated. At 5 V bias, the responsivity of the device was 30.5 mA/W and 93.7 mA/W under the 254 nm illumination and the visible illumination, respectively. And the detectivity was 1.61 × 1011 Jones and 2.14 × 1011 Jones, respectively. The photocurrent of the device can reach 91 % or more of the original under the 0–0.6 % bending strain.

High Responsivity Solar-Blind Ultraviolet Photodetector Based on (101)-Oriented SnO2 Nanosheets

High Responsivity Solar-Blind Ultraviolet Photodetector Based on (101)-Oriented SnO₂ Nanosheets

High-performance self-powered solar-blind ultraviolet photodetector based on a 4H-SiC/ZnGa2O4 heterojunction and its application in optical communication

With the urgent demand for low power consumption, environment-friendly, and portable devices, self-powered solar-blind ultraviolet (UV) photodetectors that only rely on built-in electric fields without external power sources have received extensive attention. In this paper, we have demonstrated a self-powered solar-blind UV photodetector based on a 4H-SiC/ZnGa2O4 heterojunction, along with its application in optical communication. At 0 V bias, the device exhibits a peak responsivity of 115 mA/W with an external quantum efficiency of 58.4% at 244 nm, a fast response speed with a rise/decay time of 18.36/16.15 ms, and a high UV-vis rejection ratio of 4.5 × 104, suggesting that the device has an excellent self-powered solar-blind UV photodetection performance. The exceptional performance of the photodetector is mainly attributed to the 4H-SiC/ZnGa2O4 type I heterojunction with a large conduction band offset (ΔEC = 0.99 eV) and a large valence band offset (ΔEV = 0.75 eV), which is determined by the x-ray photoelectron spectroscopy technique. Moreover, the solar-blind UV optical communication is realized by utilizing the 4H-SiC/ZnGa2O4 heterojunction device to receive signals modulated by the solar-blind UV light. This work provides an effective approach to realizing high-performance self-powered solar-blind UV photodetectors and their potential applications in optical communication.

Study on the structural, optical and electrical properties of N-doped Ga2O3 films synthesized by sol-gel method

Ga2O3 exhibits great potential for applications in solar-blind ultraviolet photo detector, high-power electronic devices and solid-state light-emitting due to its ultra-wide band gap and high Baliga figure of merit. Here, Ga2(NxO1-x)3 films with varied nitrogen contents were prepared by the sol-gel technique. XRD analysis reveals that nitrogen doping contributes for growth of greater crystalline and SEM-EDS measurements confirm that the monoclinic crystal structure of Ga2(NxO1-x)3 is maintained to doping level of 3.26wt%; FTIR information indicates that nitrogen prefers to substitute for the O1 and O2 site of Ga2O3; XPS offers evidence that nitrogen tends to occupy oxygen vacancies and generate more gallium vacancies; UV-VIS shows that impurity defects appear above valence band, and the absorption position undergoes a red shift with nitrogen above 1.32wt%; PL shows Ga2(NxO1-x)3 films can emit light of various colors under excitation at 325nm, and the acceptor level is at 1.63eV∼2eV above the valence band; The conductivity of Ga2(NxO1-x)3 films is changed from n-type to p-type when nitrogen-doping is 0.96 wt% and the I–V curve composed of Ga2(NxO1-x)3 and Ga2O3 shows PDCR = 43 under the 254nm light. Therefore, the development of nitrogen-doped β-Ga2O3 has potential opportunities for applications in photoelectric devices.