Blind Ultraviolet Photodetectors Research Articles

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

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.

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

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.

Al2O3 barrier layer for enhancing UV to visible rejection ratio in p-Si/n-MgZnO heterojunction visible blind UV photodetectors

The fabrication of visible blind ultraviolet photodetectors based on p-Si/n-MgxZn1-xO heterojunction is challenging due to the generation of visible photoresponse caused by the drift of visible light generated electrons from p-silicon to n-MgxZn1-xO across the interface. Here, it is shown that by incorporating a thin ∼30 nm Al2O3 interlayer at the heterojunction, the UV-to-visible rejection ratio in p-Si/n-Mg0.25Zn0·75O photodetectors can be significantly enhanced. The Al2O3 interlayer inserted between n-Mg0.25Zn0·75O and p-Si serves as an effective blocking layer against the transport of visible light-generated electrons from p-Si to n-Mg0.25Zn0·75O, thereby suppressing the visible photoresponse. As a result, the UV-to-visible rejection ratio was improved by approximately three orders of magnitude, with a peak responsivity of 0.17 mA/W at 270 nm and a reverse bias of 0.5 V. This high degree of visible blindness of p-Si/n-Mg0.25Zn0·75O heterojunction photodetectors with an Al2O3 barrier layer holds promise for next-generation visible-blind UV photodetection applications.

High sensitivity Ga2O3 ultraviolet photodetector by one-step thermal oxidation of p-GaN films

Gallium oxide (Ga2O3), with an ultra-wide bandgap, is a promising semiconductor material for the manufacture of solar blind ultraviolet photodetectors. The Ga2O3 thin films were successfully prepared by simpler feasible one-step thermal oxidation of p-GaN thin films, which were oxidized at 900 °C with varying oxidation times in the environment with an argon-oxygen ratio of 1000. The effect of different oxidation durations on the physical properties of the Ga2O3 thin films was studied, and particularly, the photoelectric performance of the Ga2O3 thin films was further analyzed. Compared with the GaN thin film, the dark current of the photodetector was approximately reduced by 2.31 × 104 times while the photocurrents of the device maintain the same order of magnitude, causing large photo-to-dark current ratios (PDCRs) of 2.29× 104. Furthermore, the device exhibits impressive characteristics such as high responsivity of 2.13 A/W, super high external quantum efficiency (EQE) of 1040.13%, large detectivity (D) of 1.65 × 1011 Jones, and fast response speed of 0.218/0.112 s under UV light illumination of 254 nm wavelength at −5 V bias. The results indicate that the one-step thermal oxidation can be used as a good application for preparing the device with high sensitivity, fast response and the high-resolution detection.

High performance amorphous Ga<sub>2</sub>O<sub>3</sub> thin film solar blind ultraviolet photodetectors decorated with Al nanoparticles

Gallium oxide (Ga<sub>2</sub>O<sub>3</sub>) as a wide bandgap semiconductor material has attracted much attention in the field of solar blind ultraviolet photodetection recently. Localized surface plasmon resonance is considered an effective way to improve the performance of optoelectronic devices by decorating the materials with metal particles. Al nanoparticle is a potential candidate for ultraviolet photodetectors because its suitable resonance wavelength is located in the ultraviolet wavelength range. In this work, the preparation temperature of the Ga<sub>2</sub>O<sub>3</sub> thin film is reduced by ultraviolet photo-annealing, and the amorphous Ga<sub>2</sub>O<sub>3</sub> thin film is prepared by using the solution method. In addition, aluminum (Al) nanoparticles are used to decorate the surface of Ga<sub>2</sub>O<sub>3</sub> thin film through thermal evaporation of aluminum film and then annealing, which improves the optoelectrical performance in the solar-blind wavelength spectrum. The X-ray diffraction (XRD) is employed to demonstrate the amorphous Ga<sub>2</sub>O<sub>3</sub> thin film. The surface roughness and the diameters of Al nanoparticles are analyzed by atomic force microscope (AFM). When the thickness of the deposited Al layer is about 3–5 nm, Al particles with the diameters in a range of 2–3 nm can be obtained. When the thickness of the deposited Al layer is more than 7 nm, Al nanoparticles turn into the particles with non-identical diameters and distribute in the form of agglomeration. Transmittance spectrum and absorption spectrum are employed to characterize the optical properties. The bandgaps of different samples are obtained, and the results are consistent with the theoretical ones. The Ga<sub>2</sub>O<sub>3</sub> thin film shows excellent optoelectrical performance and solar blind rejection ratio. Under 254 nm illumination, the maximum photo-to-dark current ratio is 2.55×10<sup>4</sup>, and the rejection ratio of <i>I</i><sub>254 nm</sub>/<i>I</i><sub>365 nm</sub> is 2.2×10<sup>4</sup>. The best responsivity and detectivity of prepared samples are 0.771 A/W and 1.13×10<sup>11</sup> Jones, which are about 34 times and 36 times higher than those without Al decoration. The improvement is attributed to the scattering effect of surface Al nanoparticles for illumination, which enhances the Ga<sub>2</sub>O<sub>3</sub> thin film absorption of solar blind ultraviolet light. Meanwhile, owing to the localized surface plasma resonance, the local electromagnetic fields generated near the Al nanoparticles promote the transfer of carriers in the film. Furthermore, the point about how the Al nanoparticles decorated on the surface of Ga<sub>2</sub>O<sub>3</sub> thin film influence the time response is also discussed in this work. As a result, the introduction of defect states will lead to an increase of fall time due to the Al deposition. In this work, the effect of Al nanoparticles decoration on the optoelectrical performance of amorphous Ga<sub>2</sub>O<sub>3</sub> thin film solar blind ultraviolet photodetectors is studied based on a simple preparation, which provides a possible pathway for developing the flexible solar blind electronic devices in the future.

Effects of geometric parameters on photoemission of AlGaN nanowire array photocathode

In recent years, with the continuous development of solar blind ultraviolet photodetectors, III-V compounds are widely used as semiconductor materials. The nanowire array structure has excellent ‘light trapping effect’. However, if the distance of nanowire is too close, the secondary absorption problem of the nanowire will occur. If the distance of nanowire is too far, the number of photocarriers generated in the nanowire array per unit volume will be reduced. Meanwhile, the absorption capacity of the nanowire structure with different shapes is different. Based on this background, we studied the influence of the period and geometry of AlGaN nanowires with different Al components on the optical response properties. The finite time domain difference (FDTD) method was used to compare the quantum efficiency and collection efficiency of AlGaN nanowires with different Al components, we found that the quantum efficiency of the hexagonal nanowire array with Al component of 0.42 is as high as 45%, which is the highest in our structure. At the same time, its cutoff wavelength is at 280 nm, which has excellent solar blindness. Therefore, the study in this paper can provide some theoretical reference for the experiment and preparation of AlGaN photocathode.

Thermal lensing‐induced soliton molecules in β‐phase gallium oxide

AbstractIn recent years, beta gallium oxide () has become the most investigated isomorph of gallium oxide polymorphs, due to the great potential it represents for applications in optoelectronics and photonics for solar technology, particularly in blind ultraviolet photodetector solar cells (SBUV) designs. To optimize its use in these applications, and to identify possible new features, knowledge of its fundamental properties is relevant. In this respect, optical, thermal and electronic properties of have been studied experimentally, providing evidence of a wide‐band inorganic and transparent semiconductor with a Kerr nonlinearity. Thermo‐optical properties of the material, probed in SBUV sensing experiments, have highlighted a sizable heat diffusion characterized by a temperature gradient along the path of optical beams, quadratic in beam position and promoting a refractive‐index change with temperature. The experimentally observed Kerr nonlinearity together with the thermally induced birefringence, point unambiguously to a possible formation of soliton molecules during propagation of high‐intensity fields in . To put this conjecture on a firm ground we propose a theoretical analysis, based on the cubic nonlinear Schrödinger equation in 1 + 1 spatial dimension, in which thermal lensing creates an effective potential quadratic in the coordinate of beam position. Using the non‐isospectral inverse‐scattering transform method, the exact one‐soliton solution to the propagation equation is obtained. This solution features a bound state of entangled pulses forming a bright‐soliton molecule, in which pulses are more or less entangled depending on characteristic parameters of the system.

Research of nanopore structure of Ga2O3 film in MOCVD for improving the performance of UV photoresponse

Using the mechanism of self-reactive etching between Ga and Ga2O3, Ga2O3 nanopore films were fabricated. The self-reactive etching effects based on as-grown and annealed Ga2O3 films by metal organic chemical vapor deposition were compared. It was found that the nanopore film based on as-grown Ga2O3 film has a uniform size, high density and a small diameter. Ultraviolet-visible light reflection spectra and transmission spectra show that the nanopore film could effectively reduce the reflectivity of light and enhance the light absorption. Based on the as-grown Ga2O3 film and its nanopore film, metal-semiconductor-metal structure solar blind ultraviolet photodetectors (PD) were fabricated. Under 5 V bias, the light-dark current ratio of the nanopore film PD is about 2.5 × 102 times that of the film PD, the peak responsivity of the nanopore film PD is about 49 times that of the film PD. The rejection ratio is 4.6 × 103, about 1.15 × 102 times that of the film PD. The nanopore structure effectively increases the surface-volume ratio of film. The photoelectric detection performance and response performance of the nanopore film PD could be significantly enhanced.

Low-temperature processed high-performance visible–transparent Ga2O3 solar blind ultraviolet photodetectors with the indium–tin–oxide electrode

High-performance visible–transparent electronics are being used as emerging technologies in next-generation ‘see-through’ devices. In this work, the high-performance fully visible–transparent metal–semiconductor-metal (MSM) interdigitated Ga2O3 solar blind ultraviolet (UV) photodetector (PD) was successfully fabricated by using the ITO electrode. The Ga2O3 film and the ITO electrode were grown on the sapphire substrate by the radio frequency magnetron sputtering method at a low temperature. It is demonstrated that the Ga2O3 film is the single crystal film with the (−201) crystal plane orientation, and its bandgap can be obtained around 4.8 eV. Compared with the control tradsitional opaque PD with the Ti/Au metal electrode, the fully visible–transparent solar blind UV PD with the ITO electrode showed a larger photocurrent of 1.8 µA and responsivity of 181.03 A W−1 at the bias voltage of 20 V. The external quantum efficiency (EQE) even reached 88 198%, and photo-to-dark current ratio achieved 4.8 × 105. Besides, the PD with the ITO electrode also had a shorter response time and good electrical stability after multiple light cycles. The fabricated fully visible–transparent Ga2O3 solar blind UV PD is among the best reported Ga2O3 UV PDs and shows the great potential for the next generation of ‘see-through’ functional devices.

Crystalline properties of ε-Ga2O3 film grown on c-sapphire by MOCVD and solar-blind ultraviolet photodetector

Heterogeneous epitaxy of ε-Ga2O3 films on c-plane sapphire was carried out by metal-organic chemical vapor deposition. The crystal quality and epitaxial relationship were investigated by X-ray diffraction and transmission electron microscopy. The effects of the thickness changing on crystal quality and morphology of ε-Ga2O3 films were analyzed. A higher quality ε-Ga2O3 film with full width at half maxima of 0.46° was obtained at 480 nm. A ε-Ga2O3 metal-semiconductor-metal solar blind ultraviolet photodetector with large on/off ratio of over 2 × 103, peak responsivity of 146 A/W and detectivity of 1.2 × 1013 Jones was fabricated, indicating good optical properties of the ε-Ga2O3 film.

Responsivity improvement of a packaged ZnMgO solar blind ultraviolet photodetector via a sealing treatment of silica gel

A packaged high performance ZnMgO solar-blind UV photodetector is prepared via a silica gel sealing treatment. The responsivity and stability of the device is improved according to this sealing treatment.

ZnO nanorod based highly selective visible blind ultra-violet photodetector and highly sensitive NO2 gas sensor

By using 1D ZnO nanorod, obtained from a simple two step chemical method as the sensor material, we report the fabrication of highly selective metal-semiconductor-metal (MSM) ultraviolet (UV) photodetector and NO2 gas sensor. The fabricated MSM UV photodetector and gas sensor possesses simplicity in material synthesis and sensor design. The effect of morphological evolution and structural intactness on the sensing properties of UV photodetector and NO2 gas sensor are deeply studied. The well aligned 1 dimensional (1D) ZnO nanorod provides high surface area for the sensing mechanism. The UV photodetector possesses high responsivity in the UV A region (364.81 A/W) with fast photoswitching characteristics at 5 V bias. It shows formation of good ohmic contact between metal semiconductor junctions. NO2 sensing measurement was carried out at relatively lower temperature of about 175 °C. The ZnO nanorods are highly selectivity towards NO2 gas and maximum gas response observed is 35 at 40 ppm of NO2. The NO2 gas sensor shows good repeatability at lower gas concentration of 2 ppm. The present synthesis technique provides cost effective route for obtaining highly ordered ZnO nanorods with simple sensor technology for multifunctional ZnO nanorod sensor.

Visible blind ultraviolet photodetector based on CH3NH3PbCl3 thin film.

We report a prototypical device of CH3NH3PbCl3 film ultraviolet photodetectors that were fabricated with a coplanar metal-semiconductor-metal Au interdigital electrode configuration. Pure phase CH3NH3PbCl3 films with a good crystallinity were formed by a hybrid sequential deposition process featured with inter-diffusion of PbCl2 and CH3NH3Cl upon annealing. The CH3NH3PbCl3 film photodetector exhibits a high responsivity of 7.56 A /W at 360 nm, a ultraviolet/visible rejection ratio (R360 nm/R500 nm) was about two orders of magnitude and fast response speed with a rising time of 170 μs and a decay time of 220 μs. All the above results demonstrate CH3NH3PbCl3 film photodetector as a competitive candidate in the application of visible blind UV detectors.

High-performance visible blind ultraviolet photodetector based on KTaO3 single crystal.

We report a visible-blind ultraviolet photoconductive detector with interdigitated electrodes based on KTaO3 (KTO) single crystals. Both the steady spectral responses and the transient photovoltaic measurements clearly exhibit a cutoff wavelength at 344 nm (∼3.6 eV), in accordance with the bandgap of KTO. The KTO photodetectors show a low dark current ∼1.5 pA at 20 V, and a high UV-to-visible rejection ratio with 3 orders of magnitude at room temperature. The quantum efficiency is 37.49% under 20 V bias, and the detectivity D* of 3.85×1012 cm·Hz0.5/W, which is comparable to that of silicon photodetectors in the UV region. The rise time of photoelectric response is ∼260 ps, indicating an ultrafast photoelectric response characteristic. The present work offers appealing prospects for the application of KTO materials in high-performance visible blind ultraviolet photodetectors.

(Invited) Neutron Irradiation Effect on GaN-Based Materials

For the predominant property, GaN becomes a promising material for ultraviolet/ blue light-emitting diode, solar blind ultraviolet photodetector, radiation resistant particle detectors, and high power high temperature electronic devices. Because of the radiation hardness of GaN, those devices have the potential to be used in outer space and other radiation environment. Irradiation induced defects play the main role in the reliability of GaN based devices. Recently, a strong effort by several groups was devoted to the analyses of electrical and optical properties of defects and their interaction by irradiating GaN with electrons, ions, neutrons and protons [1–4], which is very important for the devices operating at extreme harsh environment. Positron annihilation spectroscopy (PAS) with a slow-positron beam is an efficient tool for the investigation of open-volume defects such as vacancies in semiconductors, at which they get trapped. In a vacancy the electron density is decreased which makes the positron lifetime longer and narrows the positron-electron momentum distribution. The latter can be observed by recording the Doppler broadening of the energy spectrum of the annihilation radiation. Especially the momentum distribution of the core electrons is sensitive to the chemical environment of an annihilation site. However, in the case of light elements such as O or N the annihilation probability with the core electrons is negligible. The samples used in the present work were grown on C-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD) with unintentionally doped and Si doped. A 20 nm low temperature GaN nucleation layer was initially grown, and 4 μm GaN film grown at 1050°C was followed. The sample was cut into small pieces with an area of about 10×10 mm2, and irradiated with 2MeV proton from heavy ion accelerator. The incident fluence is 1014, 1015, or 1016 cm-2, respectively. Positron annihilation spectroscopy, XRD, and Raman spectra were measured. Irradiation induced defect is vacancies which increased with incident proton. XRD result shows that the crystal-order was kept after proton irradiation. Raman spectra of the Si doped sample shows a “carrier removal” effect but there is not any change in the other spectra.

Epitaxial growth of cubic Mg0.45Zn0.55O thin films on SrTiO3 (001) substrate with MgO buffer layer

Cubic Mg0.45Zn0.55O thin films with MgO buffer layer were epitaxially grown on SrTiO3 substrate by radio frequency oxygen plasma assisted molecular beam epitaxy. X-ray diffraction measurements indicate high quality single crystal films of (200) orientation. The growth follows cubic-on-cubic alignment with epitaxial relationship of Mg0.45Zn0.55O (001)[100]//MgO (001)[100]//SrTiO3 (001)[100]. Atomic force microscopy measurements reveal a smooth surface with the rms roughness of 0.36nm in an area of 5×5μm2. The band gap of the film is calculated to be 4.8eV and in the solar blind range. Since the MgO buffer layer can suppress the sub-band-gap photoresponse from the SrTiO3 substrate and does not absorb moisture like the bare MgO substrate, the Mg0.45Zn0.55O thin films with MgO buffer layer grown on SrTiO3 substrate have promising applications in solar blind ultraviolet photodetectors.

Enhanced ultraviolet photoconductivity in semiconducting ZnGa2O4 thin films

We have investigated the conductivity and photoconductivity response of undoped and Li-doped ZnGa2O4 epitaxial films grown using pulsed-laser deposition. A significant enhancement of the ultraviolet (UV) photoresponse is observed with Li doping that also correlates with an enhanced luminescent intensity. The wavelength dependence observed for creation of free carriers under UV excitation suggests that the transition is either band-to-band or involves a defect level near the band edge. Moderate n-type dark conductivity is observed for undoped films processed under reducing conditions. With Li doping, dark conductivity is reduced, suggesting that lithium ions in the zinc gallate lattice serve as deep acceptors. In addition, Li doping effectively eliminates persistent photoconductivity that is commonly observed in undoped films, suggesting the possible use of Li-doped ZnGa2O4 as a visible wavelength blind UV photodetector.

Ultraviolet photoconductive detector based on epitaxial Mg0.34Zn0.66O thin films

We report on the fabrication and characterization of visible blind ultraviolet photodetectors based on MgxZn1−xO. Using pulsed laser deposition technique, Mg0.34Zn0.66O thin films with a bandgap of 4.05 eV were epitaxially grown on c-plane sapphire substrates. The structural, electrical, and optical properties of epilayers were characterized using various techniques. Based on the Mg0.34Zn0.66O films, planar geometry photconductive type metal–semiconductor–metal photodetectors were fabricated. At a 5 V bias, a high responsivity of 1200 A/W was achieved at 308 nm, and the visible rejection (R308 nm/R400 nm) was more than four orders of magnitude. The 10%–90% rise and fall time were 8 ns and 1.4 μs, respectively.