Solar-blind Ultraviolet Photodetectors Research Articles

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.

Ultrasensitive Narrowband Organic Phototransistor for Solar-Blind Ultraviolet Detection and Imaging

Solar-blind ultraviolet (SBUV) photodetectors has extensive applications in fields such as military operations, agriculture, and flame detection. However, most current ultraviolet detection is based on inorganic materials, and there is...

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

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.

Effects of film thickness on crystal structure, surface topography, optical, and photoelectric properties of Ga2O3 thin film based solar blind photodetectors

β-Ga2O3 epitaxial thin films with different thicknesses were grown on Al2O3 (0001) substrates by the pulse laser deposition technology. The full width at half maximum of XRD rocking curve, grain size, surface roughness, and optical absorbance (200–300 nm) of the β-Ga2O3 films increase with increasing film thickness. In addition, with increasing film thickness, the adsorption edge presents a red-shift phenomenon, which is accompanied by a slight decrease in the optical band gap (). The metal-semiconductor-metal type photodetector made with the 401-nm β-Ga2O3 film shows the maximal photocurrent (1.06 μA @ 10 V), photo-to-dark current ratio (6.96 × 104), responsivity (90 mA W−1), and detectivity (0.5 × 1011 Jones) under 254-nm UV light illumination with a light intensity of 98.4 μW/cm2. Moreover, the 401-nm photodetector displays a small rise time of 0.111/0.561 s and a decay time of 0.046/0.047 s as well as a good stability and repeatability. These findings provide useful reference for the fabrication of β-Ga2O3 film based solar blind ultraviolet photodetectors.

Recent Progress in Source/Drain Ohmic Contact with β-Ga2O3

β-Ga2O3, with excellent bandgap, breakdown field, and thermal stability properties, is considered to be one of the most promising candidates for power devices including field-effect transistors (FETs) and for other applications such as Schottky barrier diodes (SBDs) and solar-blind ultraviolet photodetectors. Ohmic contact is one of the key steps in the β-Ga2O3 device fabrication process for power applications. Ohmic contact techniques have been developed in recent years, and they are summarized in this review. First, the basic theory of metal–semiconductor contact is introduced. After that, the representative literature related to Ohmic contact with β-Ga2O3 is summarized and analyzed, including the electrical properties, interface microstructure, Ohmic contact formation mechanism, and contact reliability. In addition, the promising alternative schemes, including novel annealing techniques and Au-free contact materials, which are compatible with the CMOS process, are discussed. This review will help our theoretical understanding of Ohmic contact in β-Ga2O3 devices as well as the development trends of Ohmic contact schemes.

Flexible self-powered solar-blind UV photodetectors based on amorphous Ga2O3 modified carbon fiber cloth

Self-powered solar-blind ultraviolet (UV) photodetectors are gaining increasing recognition as green, efficient, and sustainable devices, representing a development trend in the evolution of next-generation optoelectronics. Much efforts have been devoted to carbon-based materials for their excellent conductivity. Among these materials, commercial carbon fiber sheets stand out due to their distinctive 3D structure, impressive conductivity, cost-effectiveness, and flexibility, rendering them highly suitable for a wide range of photosensitive applications. The realm of flexible optoelectronic devices has garnered substantial interest owing to its pivotal role in diverse domains. However, the utilization of carbon cloth (CC) as a substrate for photodetectors remains an area ripe for exploration. This study aims to fabricate self-powered solar-blind UV photodetectors based on amorphous Ga2O3 (a-Ga2O3) thin films modified CC using a concise and efficient physical vapor deposition technique (magnetron sputtering). The results show that the optimal responsivity of the a-Ga2O3/CC photodetector is 16.98 mA/W, with response times of 0.16/0.10 s (rise/decay time). Even after 300 cycles of bending treatment, this self-powered photodetector maintains excellent cyclic stability and repeatability. Furthermore, first-principles calculation reveals a significant built-in electric field around the interface between a-Ga2O3 and CC, which can effectively separate photogenerated electrons and holes and suppress carriers’ recombination. This inherent mechanism allows the a-Ga2O3/CC-based photodetector to exhibit remarkable self-powered characteristics and prominent solar-blind detection ability.

Zn-doping induced phase control mechanism of Ga2O3 thin films by spray pyrolysis deposition for application of solar-blind ultraviolet photodetector

Ga2O3 polymorphs have attracted considerable attention for optoelectronic and electronic device applications with high durability. Despite the many investigations, the crystal phase of Ga2O3 is difficult to control at low temperatures. In this study, the phase of Ga2O3 was controlled by Zn-doping at 500 °C by spray pyrolysis deposition. The pristine Ga2O3 showed the mixed α- and ε-phases, which disappeared with increasing Zn content from 0 to 60%. A single β-phase Ga2O3 thin film was formed when the Zn content was 60%. As the Zn content was increased to 120%, ZnO particles formed on the β-phase Ga2O3 surface. Therefore, the Zn dopants substitute for the Ga site and modify its coordination in the Ga2O3 matrix to form a β-phase Ga2O3. The β-Ga2O3 based solar-blind ultraviolet photodetector exhibited 1.645/0.581 s response times, a responsivity of 3.93 × 10−4 A W−1, and a detectivity of 2.65 × 1010 Jones under a bias voltage of 20 V.

Enhancing the performance of ZnGa2O4 metal-semiconductor-metal ultraviolet solar-blind photodetectors by surface fluorine plasma sensitization

ZnGa2O4 has a wide direct bandgap and excellent optical properties and is an emerging material for use in solar-blind ultraviolet (UV) photodetectors (PDs). Recently, metal-semiconductor-metal (MSM) based devices have gained popularity because of their low production cost, minimal design, flexible integration, and tunable performance. However, such devices suffer from low sensitivity. Herein, we propose a sensitization engineering strategy that involves surface fluorine plasma (SFP) treatment to enhance the performance of a ZnGa2O4 MSM solar-blind UV PD. Through this strategy oxygen vacancy defects are simultaneously passivated and the ratio of adsorbed oxygen species on the surface of the ZnGa2O4 thin film is changed. These modifications optimize the current under both dark and light conditions. In particular, the dark current has a trade-off relationship between the reduction in the oxygen vacancy concentration and changes in the crystal grain boundaries. As a result, the photocurrent is enhanced because of the increased amount of adsorbed oxygen. The PD prepared using a ZnGa2O4 thin film treated by SFP for 15 min exhibited excellent performance, specifically, it showed a large responsivity (42.22 A/W) and good specific detectivity (5.72 × 1014 Jones). Notably, these values are superior to those of most reported MSM solar-blind PDs. Moreover, the excellent rejection ratio and durability during repeated use demonstrate the benefits of SFP treatment for enhancing operating stability. Our study provides an effective avenue for optimizing the optoelectronic performance of oxide semiconductors.

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.