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AlGaN/GaN Schottky barrier diode (SBD) temperature sensor with low turn-on voltage was fabricated by employing the recessed anode structure. This AlGaN/GaN SBD demonstrates good rectification in a broad temperature scope from 298 to 473 K. Compared with common planar diode, the recessed anode SBD shows a relatively lower turn-on voltage and better Schottky contact characteristics. The temperature-dependent forward voltage at a fixed current displays great linearity, contributing to a sensitivity of about 1.0 mV/K. The calculated sensitivities exhibit the downtrend by increasing current level, which is in agreement with the thermionic emission (TE) model. The recessed anode AlGaN/GaN SBDs show good potential in temperature sensor application.

High-performance solar-blind UV detector with high response and fast speed is needed in multiple types of areas, which is hard to achieve in one device with a simple structure and device fabrication process. Here, the effects of Ag nanoparticles (NPs) with different sizes on UV response characteristics of the device are studied, the Ag NPs with different sizes that are made from a simple vacuum anneal method. Ag NPs with different sizes could modulate the peak response position of the mixed-phase MgZnO detector from near UV range (350 nm) to deep UV range (235 nm), and the enhancement effect of the Ag NPs on the UV response differs much with the crystal structure and the basic UV response of the MgZnO thin film. When high density 20-40 nm Ag NPs is induced, the deep UV (235 nm) response of the mixed-phase MgZnO detector is increased by 226 times, the I uv/I dark ratio of the modified device is increased by 17.5 times. The slight enhancement in UV light intensity from 20 to 40 nm Ag NPs induces multiple tunnel breakdown phenomena within the mixed-phase MgZnO thin film, which is the main reason for the abnormal great enhancement effect on deep UV response of the device, so the recovery speed of the modified device is not influenced. Therefore, Ag NPs with different sizes could effectively modulate the UV response peak position of mixed-phase MgZnO thin films, and the introduction of Ag NPs with high density and small size is a simple way to greatly increase the sensitivity of the mixed-phase MgZnO detector at deep UV light without decreasing the device speed. Published version This work was supported by the National Natural Science Foundation of China under grant nos. (51872187, 11774241, 51371120, 51302174, 61704111, 61504083, and 61574051), the Natural Science Foundation of Guangdong Province (2016A030313060 and 2017A030310524), the Public Welfare Capacity Building in Guangdong Province (2015A010103016), the Project of Department of Education of Guangdong Province (2014KTSCX110), the Science and Technology Research Items of Shenzhen (JCYJ20170818144255777, JCYJ20170818144212483, JCYJ20180507182248925, JCYJ201602261920, JCYJ20170818143417082, and JCYJ20160226192033020), the Science and Technology Foundation of Shenzhen, and the National Key Research and Development Program of China (2017YFB0404100 and 2017YFB0403000).

In this study, pulsed laser deposition method (PLD) was employed to grow MgxZn1-xO films on quartz substrates. The optimal deposition temperature of 300 °C for MgxZn1-xO film was decided and Mg0.38Zn0.62O, Mg0.56Zn0.44O and Mg0.69Zn0.31O films were grown respectively using MgxZn1-xO targets with different Mg contents (x = 0.3, 0.5 and 0.7). As-deposited Mg0.38Zn0.62O film possessed the mixed-phase (hexagonal and cubic phase) structure, appropriate band gap of 4.68 eV and smaller surface roughness of 1.72 nm, and the solar-blind photodetector (PD) based on it was fabricated. The key features of our PD are the cutoff wavelength of 265 nm lying in solar-blind band, lower dark current (Idark) of 88 pA, higher peak responsivity of 0.10 A/W and bigger Ilight/Idark ratio of 1688, which provide the new idea for the application of solar-blind PDs based on MgxZn1-xO films.

In this paper, we report aqueous solution-processed boron-doped gallium oxide dielectric thin films for high-performance oxide thin-film transistors. The role of B incorporation on the microstructu...

Recently, metal surface plasma technology has been widely used to improve the quantum efficiency of optoelectronic devices, such as ZnO light-emitting diodes (LEDs). In this work, Ag films with the appropriate thickness were prepared by evaporation and annealed, and a layer of ZnCdO films with different Cd concentrations was grown on the Ag films by the pulsed laser deposition method. During this process, the changes in the Cd concentrations caused the near-band edge (NBE) emission of the ZnCdO films to be continuously adjusted in the ultraviolet to green wavelength range by controlling the oxygen pressure. The prepared Ag nanoparticles and ZnCdO composite films were used to study the metal localized surface plasmon (LSP) effect. The results show that the enhanced or reduced photoluminescence intensity of ZnCdO NBE depends on the probability of electrons transport to either the LSP level or the Fermi level of the metal. This discovery provides an important theoretical basis for the preparation of ZnCdO semiconductor LEDs in the future.

A p-GaN/i-MgO/n-ZnO nanorod array (NRA) heterojunction light-emitting diode has been fabricated. Its room-temperature electroluminescence spectra under different forward biases revealed a strong emission band across the whole visible region, which was blue-shifted when increasing the forward bias. The origin of this visible emission is considered to be related to oxygen vacancy (VO) defects in different valence states, where the blue emission (∼ 460 nm) comes from neutral oxygen vacancy (VOX ) defects and the green emission (∼ 520 nm) from singly charged oxygen vacancy (VO+ ) defects, while the yellow (∼ 580 nm) and red emission (∼ 670 nm) are attributed to doubly charge oxygen vacancy (VO++ ) defects. These VO defects in different states can convert into one another under different excitation conditions, resulting in the blue-shift of the emission peak as the forward voltage is increased.

As an n-type oxide semiconductor, Ga2O3 shows great promise in solar-blind ultraviolet (UV) photodetectors due to its adequate band gap, high absorption coefficient, high thermal and chemical stability, high breakdown voltage, and high sensitivity to UV light. In order to investigate the photoresponse of the Ga2O3 photodetector with different crystallization status, we fabricated a series of β-Ga2O3 thin films on a sapphire substrate via pulsed laser deposition with different deposition temperatures from 250°C to 650°C. X-ray diffraction and scanning electron microscopy result showed crystallization enhancement due to the increasing of deposition temperature, and the crystallization procedure started at ∼ 450°C. Optical analysis indicated a blue shift present at the absorption edge (from 4.6 eV to 5.1 eV) with temperature increasing from 450°C to 650°C, showing modulation feasibility in the band gap due to temperature dependence. In addition, all samples showed high transmittance (over 90%) over the entire visible spectrum. Film detectors fabricated by these samples showed high photoresponse and high light/dark current ratio (ILight/IDark) on Ga2O3 deposited at 450°C. Transmission electron microscopy result for film deposited at 450°C showed that the top and bottom regions of films contained both amorphous and crystalline Ga2O3, while there was no crystallization in the middle area of the film, indicating that a combined amorphous-crystalline Ga2O3 film with adequate ratio of crystalline state can significantly enhance the photoresponse while restraining the dark current.

Thin-film transistors (TFTs) based on solution-derived metal oxides hold great potential in emerging low-cost large-area printed electronics. Despite recent impressive progress, these device performances are far behind those of their corresponding vacuum-based counterparts, impeding their future commercialization. In this work, we designed and created high-performance TFTs based on a nanometer-thick (down to 5 nm) crystalline In–Sm–O channel via aqueous solution processing, with a performance comparable to those of existing vacuum-processed metal oxides. The microstructural, chemical, optical, and electrical properties of the ultra-thin In–Sm–O samples as a function of Sm doping content (0–10%) were comprehensively investigated. The In–Sm–O TFTs (5% Sm) on SiO2/Si dielectrics demonstrated state-of-the-art performance, including a high mobility of 21.51 ± 1.33 cm2 V−1 s−1, subthreshold swing of 0.66 ± 0.06 V per decade, threshold voltage of 2.14 ± 0.44 V, on/off current ratio >108, and remarkable bias stress stability. The success of In–Sm–O was attributed to the high quality of the crystalline In2O3 matrix, the ideal nature of Sm dopant in suppressing oxygen vacancies, as well as the ultrathin and atomically smooth nature of the channel layer. Therefore, the aqueous solution-processed ultra-thin In–Sm–O channel is expected to enable the realization of future low-cost, large-area, and high-performance green electronics.

Au/MgZnO/nanolayered ZnO (Ga-doped)/In MIS (metal–insulator–semiconductor) structure UV detectors are fabricated by the PLD (pulsed laser deposition) method, and the effect of different thickness G...

Transparent amorphous oxide semiconductor (TAOS) represented by a-InGaZnO (IGZO) has achieved their commercial success in the display industry due to its superior material properties (e.g. high mobility (>10 cm 2 V −1 s −1 ), good transparency and excellent uniformity). However, TAOSs with excellent electrical properties are all n-type due to the particular electronic structures of oxide materials. The absence of high performance p-type TAOS limits the device application such as complimentary circuit and is now the largest drawback for oxide electronics. Here, we propose a low-temperature solution method to fabricate p-type transparent amorphous nickel oxide (NiO). The influence of processing parameters such as annealing temperature, precursor concentration, source/drain electrode, and dielectric layer is systematically investigated to maximum the NiO device performance. The optimized NiO TFT exhibits outstanding p-channel behavior, including a high hole mobility of 6.0 cm 2 V −1 s −1 , remarkable on/off current modulation ratio of ∼10 7 , and good subthreshold swing of 0.13 V/decade. The high performance NiO device is attributed to the synergistic optimization of annealing temperature, channel thickness, source/drain electrodes, and dielectric materials. The properties of our p-type TAOS are comparable with that of traditional n-type TAOS.

We report the aqueous-solution-processed Ni-doped In2O3 (NixIn2–xO3, NiInO) thin-film transistors (TFTs) for the first time. The effect of Ni doping on In2O3 microstructure, oxygen defects, and the electron transport properties are investigated by extensive characterization techniques. Analyses indicate that the oxygen vacancies in NiInO are suppressed as the Ni-doping concentration increases, leading to a lower off-state current and a positive shift in threshold voltage. The optimized NiInO TFTs exhibit a high mobility of 17.71 cm2/(V s), on/off current ratio > 106, threshold voltage of 4.21 V, and superior bias stress stability. The success of Ni doping could be attributed to the small ion radius of Ni, large Lewis acid value, and strong Ni–O bond strength. Therefore, the fabricated NiInO TFT provides a bright path for the development of high-performance oxide TFTs.

Perovskite metal oxide (LiNbO3) nanomaterial is explored as a magneto-optic sensor. The electromagnetic interaction is described by magneto-optic modulation associated with vacancy-induced room temperature ferromagnetism. The guiding and propagation through single mode fiber (SMF) is via the excitation of core modes through the material-mediated cavity and further modulated by external magnetic field. The sensitivity and resolution of the sensor are found to be 186 p.m./mT and 0.51 Oe, respectively. The structure with material integrated optical design resulting in a Fabry-Perrot interferometer (FPI), is implemented as an extrinsic sensor, and sensing mechanism is elaborated.

Vertical GaN Schottky barrier diodes (SBDs) were fabricated on Ge-doped free-standing GaN substrates grown by hydride vapor phase epitaxy. Detailed material characterization was performed, and the results indicate the superiority of Ge doping in the GaN, which contributed to the SBDs with lower stress, fewer defects and higher quality. Based on the capacitance-voltage and current–voltage measurements performed, SBDs achieved together with a low turn-on voltage Von (0.71–0.74 V), high current Ion/Ioff ratio (3.9 × 107–2.9 × 108), high Schottky barrier height (0.96–0.99 eV), and high breakdown voltage Vb (802 V for a 100 μm diameter). This shows that vertical GaN SBDs on the Ge-doped substrates are promising candidates for high power applications.

Zn1-xCdxO films with different Cd contents obtained by controlling the growth oxygen pressure (Op) were deposited on both c-sapphire (Al2O3) substrates and p-GaN substrates, by means of the pulsed laser deposition (PLD) method. Photoluminescence (PL) measurement revealed that the variation of Op influenced the amount of Cd doping into Zn1-xCdxO films deposited on Al2O3, leading tunable luminescence from the ultraviolet (UV) to blue emission extended to the green band. Then all the fabricated n-Zn1-xCdxO/p-GaN heterojunction possessed good ohmic contacts and exhibited typical rectifying characteristic of the diode. Indeed, the high luminescence from the ZnCdO layer could be attained by inserting a MgO insulator to the heterojunction interface. The fabrication of tunable n-Zn1-xCdxO/p-GaN heterojunction light-emitting diodes is available which was supported by the results of electroluminescence (EL) experiment.

MoS2 based hybrid structures have much attention due to their novel structures and potential applications in diverse areas, such as solar energy conversion, thermoelectric power generation and photo-transistors. In the present work, we have fabricated a novel sandwich structure of MoS2/InSe-nanoparticles (NPs)/MoS2 layers on SiO2/Si substrate by a combination of chemical vapor deposition and physical vapor deposition methods. The morphology of these structures was also studied using scanning electron microscopy. In addition, we have also explored the thermal properties of these hybrid sandwich structures using temperature and power-dependent Raman spectroscopy. For MoS2/InSe-NPs/MoS2 sample, the first-order temperature coefficients of E12g and A1g modes were found to be −0.01722 and −0.01575 cm−1/K, respectively, which are significantly large compared to MoS2 layers without InSe-NPs (i.e. MoS2/MoS2 sample). Further, the thermal conductivity of MoS2/InSe-NPs/MoS2 and MoS2/MoS2 samples on SiO2/Si substrate was extracted as ∼102.3 and ∼81.7 W/m-K, respectively. This work suggests an effective way to form a novel 2D-MoS2 based sandwich structure with semiconductor/metal-NPs; opening up a new scenario to understand the electronic structure of the hybrid structure, and the local strain introduced by NPs. Electron-phonon interactions at an interface can have significant effects on electrical/thermal transport through the optoelectronic devices.

By employing localized surface plasmon resonance (LSPR), the near band edge (NBE) emission intensity of ZnO films were greatly varied, while defect emission remained almost the same. This photoluminescence (PL) intensity enhancement or reduction is tunable by changing the position of Ag nanoparticles (NPs) relative to the ZnO films. The remarkable variation of the NBE emission was investigated deeply. These experimental results reveal that the Ag NPs play a key role in tuning the PL performance of the semiconductor material, where LSPR occurs.

In2Se3 nanostructures have attracted much attention due to their potential applications in diverse areas, such as solar energy conversion, thermoelectric power generation, phase change random access memories, photodetectors, and optoelectronics in the visible region. In the present work, we have fabricated various In2Se3 nanostructures on SiO2/Si substrate using a simple and single-step physical vapor deposition (PVD) method, without using metal seed layer on the substrates. Morphology, structure and phase of the as-grown In2Se3 nanostructures have been carried out using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, respectively. In addition, we have also explored thermal properties of In2Se3 nanostructures on SiO2/Si substrate using temperature and power dependent Raman spectroscopy. Further, the thermal conductivity of nanoparticles, nanospheres, and rod like flowers at room temperature were found to be ∼37.6, ∼39.5, and ∼15.6 W/m-K, respectively. This work suggests an effective way to form various novel nanostructures, opening up a new scenario to understand the vibrational properties and electron-phonon interactions of In2Se3 nanostructures.

Room-temperature-fabricated amorphous Ga2O3 is an inexpensive and highly sensitive material for high-performance solar-blind ultraviolet (UV) (220–280 nm) detectors, which are extremely useful given the widespread use of solar-blind UV photoelectronic technology in multiple areas. The UV detection characteristics of room-temperature deposited amorphous Ga2O3 thin films fabricated by a simple RF magnetron sputtering method were studied, and the deposition Ar pressure of an a-Ga2O3 thin film was varied to determine the mechanism underlying high-performance UV detection and to develop an ideal a-Ga2O3 thin film for UV detection. A high-response amorphous Ga2O3-based UV detector was made at 0.5 Pa, and the maximum response of the device reached 436.3 A W−1 under 240 nm UV light with a 25 V bias voltage, which is near the maximum values for a single-crystal β-Ga2O3 material deposited at a high temperature. An amorphous Ga2O3-based UV detector with a low Idark noise level (4.9 nA at 25 V) and a high Iuv/Idark ratio (107314.4) was made at 1.2 Pa, and the Iuv/Idark ratio of the device was near that of a UV detector based on single-crystal β-Ga2O3 with a complex metal-oxide–semiconductor field-effect transistor (MOSFET) structure. Through a comparative analysis of the electrical characteristics and the gain mechanism within amorphous Ga2O3 thin films deposited at different Ar pressures, the high UV response of the amorphous Ga2O3 detector at 0.5 Pa is found to mainly result from the quasi-Zener tunneling multiplication phenomenon between different resistance components. The low Idark value and the high signal-to-noise ratio of the amorphous Ga2O3-based detector deposited at 1.2 Pa were mainly due to more high-resistance components and a relatively higher tunneling gain in the device. In addition, the amorphous Ga2O3-based detectors showed a much shorter response time (0.08 μs for the device deposited at 0.65 Pa) and recovery time (td1 = 0.21 ms, td2 = 5.88 ms for the device deposited at 1.2 Pa) than the reported crystal semiconductor-based devices and multiple complex structure devices. Thus, the room-temperature-fabricated amorphous Ga2O3 thin film could quickly and effectively detect a faint UV light signal in the presence of a very noisy background, which is extremely important in the applications of UV detectors in wearable, flexible photoelectronic devices.

To further improve the performance of all-inkjet-printing ZnO UV photodetector and maintain the advantages of inkjet printing technology, the inkjet printing Ag nanoparticles (NPs) were deposited on the inkjet printing ZnO UV photodetector for the first time. The inkjet printing Ag NPs can passivate the surface defects of ZnO and work as surface plasmons from the characterization of photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), and finite difference time domain method (FDTD) simulation. The normalized detectivity (D*) of the Ag NP-modified detector reaches to 1.45 × 1010 Jones at 0.715 mW incident light power, which is higher than that of 5.72 × 109 Jones of the bare ZnO photodetector. The power-law relationship between the photocurrent and the incident light power of the Ag NP-modified ZnO detector is Ipc ∝ P2.34, which means the photocurrent is highly sensitive to the change of incident light power.

We reported the low-temperature high performance IGZO TFTs by solution processing. The influence of IGZO composition over broad range on thin films and devices properties were investigated by a wide range of characterization techniques. The schematic of TFT solution-processed IGZO TFTs mobility with different compositions has been obtained. In order to achieve decent TFT performance, the In content should be much high for solution-processed IGZO TFTs. The optimal solution-processed IGZO TFTs with In:Ga:Zn = 5:1:1 composition exhibited a large mobility of 9.1 cm2 V−1 s−1, low subthreshold swing of 0.22 V/decade, and high on/off ratio of 106 at 300 °C processing temperature.

High quality (200) and (111) orientations cubic MgZnO thin films were made on (200) and (111) orientations MgO substrates separately under different condition with higher and lower migration energy of reactive atoms separately. The crystal quality of (111) orientation MgZnO thin film is higher than (200) one because of the stronger horizontal migration of atoms on (111) surface under high temperature condition, the surface of (200) orientation MgZnO thin film is smoother than (111) orientation one because of lower vertical growth speed of (200) MgZnO grains. The band gap of (111) orientation MgZnO thin film is smaller than (200) one because of more Zn atoms in (111) orientation MgZnO lattice than that in (200) ones. This paper gives an effective method to improve crystal quality of different orientation MgZnO thin film under different condition, which is meaningful in application of cubic MgZnO in different areas.

ZnO:Al (AZO) and a-Ga2O3 thin films were successively deposited on a sapphire substrate by magnetron sputtering and the photoelectric properties of AZO/a-Ga2O3 heterojunction vertical structure to solar blind ultraviolet light were investigated. The device shows a high photo-to-dark current ratio (2.2 × 103), low dark current (11.4 nA), large responsivity (67.26 A/W) and fast response and recovery times of 1.53 μs and 2.25 ms under 254 nm light illumination at 10 V. Additionally, the device exhibits an obvious self-powered effect with light-dark current ratio (183.3) and the responsivity (2.92 × 10−2 A/W) at 0 V. The high response is attributed to the separation of photogenerated electron-hole pairs due to built-in field in the depletion width of AZO and Ga2O3. The analysis shows that there exists a quasi-Zener tunneling internal gain mechanism, which increases the performance of the device. The comprehensive performance of the device implied a wide potential in optoelectronics applications.

The disadvantages of the low on/off current ratio (Ion/off) and high leakage current in ZnO-based thin-film transistors (TFTs) impede its development to realize industrial production for replacing Si-TFTs. In this work, we fabricated a high performance MgZnO/ZnO dual-active-layer TFTs (DAL-TFTs) through systematic optimize the synthesis conditions. The optimized Mg0.2Zn0.8O/ZnO TFTs presents high mobility of 21.1 cm2V−1s−1 with a high Ion/off of 1.5 × 108, which is much higher than that of ZnO-based TFTs. The results indicate that high carrier concentration ZnO close to the insulation layer ensures the excellent mobility of MgZnO/ZnO DAL-TFTs and low carrier concentration MgZnO layer can reduce the off-state current of the device, and increase the switching ratio of the device. Our results indicate the MgZnO/ZnO composite is a promising candidate for high performance TFTs and other electronic devices.

MSM structure UV detectors were fabricated on mixed-phase MgZnO thin films with (200) cubic MgZnO/hexagonal MgZnO and (111) cubic MgZnO/hexagonal MgZnO interfaces by PLD method. Under 25 V bias voltage, the maximum responsivity of the mix-phase MgZnO based detector with (002) cubic MgZnO/hexagonal MgZnO interfaces reached 8 A/W at 256 nm because of 3809% internal gain of the detector at solar-blind UV light, which is two order of magnitude bigger than the detector with (111) cubic MgZnO/hexagonal MgZnO interfaces. The higher density of interface states between (200) cubic and hexagonal MgZnO grains in the mix-phase MgZnO thin film is main reason for its big internal gain and high solar-blind UV response. The Idark of the mixed-phase MgZnO based detector with (111) cubic MgZnO/hexagonal MgZnO interfaces is much smaller and the Ilight/Idark of which is higher because of the higher interfaces barrier at (111) cubic MgZnO/hexagonal MgZnO interfaces, so the detector could effectively detect faint solar-blind UV signal more under strong noise background.

We demonstrate the direct formation of c-axis oriented crystalline IGZO thin films at room temperature by magnetron sputtering. The influence of processing parameters such as oxygen partial pressure, post-annealing temperature and channel thickness on the electrical performance of IGZO films and thin-film transistors (TFTs) was intensively investigated. The as-deposited crystalline IGZO TFTs exhibited a mobility of 4.49 cm2 V−1 s−1 and an on/off ratio of 2.08 × 107. For the annealed device, a high mobility of 10.51 cm2 V−1 s−1, a subthreshold swing of 0.672 V decade−1, a threshold voltage of 0.38 V, as well as an on/off current ratio of ∼108 are achieved with an annealing temperature of 400 °C. These results present a significant step towards the development of high-performance TFTs using oriented crystalline IGZO.

We report the fabrication of gallium oxide (GaOx) thin films by a novel polymer-assisted deposition (PAD) method. The influence and mechanism of postannealing temperature (200-800 °C) on the formation and properties of GaOx thin films are investigated by complementary characterization analyses. The results indicate that solution-deposited GaOx experiences the elimination of organic residuals as well as the transformation of amorphous GaOx to crystalline GaOx with the increase in annealing temperature. High-quality GaOx could be achieved with a smooth surface, wide band gap, and decent dielectric performance. Moreover, the solution-processed In2O3 thin-film transistors based on optimized GaOx dielectrics demonstrate outstanding electrical performance, including a low operating voltage of 5 V, a mobility of 3.09 cm2 V-1 s-1, an on/off current ratio of 1.8 × 105, and a subthreshold swing of 0.18 V dec-1. Our study suggests that GaOx achieved by PAD shows great potential for further low-cost and high-performance optoelectronic applications.

High-performance ultraviolet (UV) detectors with both high responses and fast speeds are hard to make on homogeneous crystal semiconductor materials. Here, the UV response characteristics of mixed-phase MgZnO thin films with different internal structure distributions are studied. The mixed-phase MgZnO-based detector with the given crystal composition has a high response at both deep UV light (96 A W−1 at 240 nm) and near UV light (80 A W−1 at 335 nm). Meanwhile, because of the quasi-tunneling breakdown mechanism within the device, the high-response UV detector also shows a fast response speed (tr = 0.11 μs) and recovery speed (td1 = 26 μs) at deep UV light, which is much faster than both low-response mixed-phase MgZnO-based UV detectors with other structure constitutions and reported high-response UV devices on homogenous crystal materials. The Idark of the device is just 4.27 pA under a 5 V bias voltage, so the signal-to-noise ratio of the device reached 23852 at 5.5 uW cm−2 235 nm UV light. The new quasi-tunneling breakdown mechanism is observed in some mixed-phase MgZnO thin films that contain both c-MgZnO and h-MgZnO parts, which introduce a high response, signal-to-noise ratio, and fast speed into mixed-phase MgZnO-based UV detectors at weak deep UV light.

We prepared ZnO:H thin films in Ar + H2 atmosphere with substrate at room temperature by magnetron sputtering, the effect of H2 flow ratio on the properties of thin films and the performance of ZnO:H thin-film transistors (ZnO:H-TFTs) were investigated. Hydrogen could act as a defect passivator and a shallow donor in ZnO films, which not only increases the carrier concentration but also reduces the interface trap density, therefore improving the TFT performance. Compared with pristine ZnO-TFT, the optimal ZnO:H-TFT exhibits great enhancement, with the saturation mobility increasing from 2.17 cm2/V⋅s to 5.17 cm2/V⋅s, the on/off ratio increasing from 3.47 × 105 to 4.98 × 106, the threshold voltage reducing from 15.12 V to 6.03 V. Meanwhile, the positive and negative bias stability is also improved from ΔVth = 3.89 V and −6.35 V to 1.74 V and −3.72 V, respectively. Our results show that introducing hydrogen into the sputtering atmosphere to achieve hydrogen doping is a simple and effective method to improve the performance of ZnO-TFTs. Furthermore, the high-performance ZnO:H-TFTs fabricated at room temperature have great potential in the field of flexible electronics.

In this work, we report parts per billion (ppb) NO2 gas detection by utilizing zinc oxide/reduced graphene oxide (ZnO/rGO) heterostructure through a chemiresistive approach. The sensing material is carefully investigated through numerous characterization techniques. The experimental results indicated that the designed sensor shown good linearity in low ppb range of nitrogen dioxide (NO2) gas. The sensor exhibited very high response of 33.11 at 2.5 ppm in 182 s with obtained detection limit down to ppb at relatively low optimal operating temperature of 110 °C. The remarkable performance of ZnO/rGO heterostructure towards NO2 and negligible cross-response to other interfering gases along with high repeatability and long-term stability of the sensor is investigated. Due to many reactive sites and high transport capability of rGO along with high gas adsorption of ZnO nanospheres which attributes to the favorable charge transfer at ZnO/rGO interface under exposure of NO2 gas which leads to modulate the energy band structure. This study shows that the simple, cost-effective synthesis method along with easy-fabricated and deployable sensor can be applied in many industrial and environmental applications.

Volatile organic compounds (VOCs) monitoring is a vital need for many industrial and environmental air quality monitoring applications. We proposed and demonstrated a dual-cavity Fabry-Perot interferometric (DFPI) sensors fabricated by using a polarization maintaining fiber (PMF) immobilized with graphene, PMMA and graphene/PMMA composite for detection of various volatile gases. The optical properties of these materials changes when exposed to different VOCs, which proportionally leads to wavelength and power shift in an interference spectrum due to effective change in refractive index of graphene and swelling of PMMA, respectively. The experimental results are best fitted with models based on Langmuir adsorption isotherm and Hansen solubility parameters. This study focuses on insight into the physical/chemical interaction of volatile gases with versatile sensing materials along with new optical fiber configuration approach, which could be explored for remote detection and air quality monitoring.

Strain regulation as an effective way to enhance the photoelectric properties of two-dimensional (2D) transition metal dichalcogenides has been widely employed to improve the performance of photovoltaic devices. In this work, tensile strain was introduced in multilayer MoS 2 grown on GaN by depositing 3 nm of Al 2 O 3 on the surface. The temperature-dependent Raman spectrum shows that the thermal stability of MoS 2 is improved by Al 2 O 3 . Theoretical simulations confirmed the existence of tensile strain on MoS 2 covered with Al 2 O 3 , and the bandgap and electron effective mass of six layers of MoS 2 decreased due to tensile strain, which resulted in an increase of electron mobility. Due to the tensile strain effect, the photodetector with the Al 2 O 3 stress liner achieved better performance under the illumination of 365 nm wavelength, including a higher responsivity of 24.6 A/W, photoconductive gain of 520, and external quantum efficiency of 8381%, which are more than twice the corresponding values of photodetectors without Al 2 O 3 . Our work provides an effective technical way for improving the performance of 2D material photodetectors.

Perovskite mixed valence magnetic (La0.7Ba0.3MnO3) material is explored as a magneto-optical sensor by integrating onto the surface of an optical fiber. The guiding properties of core modes excited by the material cavity are modulated by the external magnetic field. The experimental results concluded that the device exhibits linear response to applied magnetic field strength in the range of 0–20 mT with the sensitivity of 228 pm/mT and resolution of 0.87 Oe. Blue-shift phenomenon has been observed in the interference pattern, when a magnetic field is applied. Such wavelength shift is attributed to the influences of magneto-optical properties on optical-wave propagation. The results reveal the feasibility of developing an index-tuneable magneto-optical sensor using perovskite magnetic material.

Indium dysprosium oxide (InDyO) thin-film transistors (TFTs) are demonstrated by aqueous solution processing. The structure, morphology, chemical, oxygen defects, optical, and electrical properties of InDyO films with the change of Dy doping contents are systematically studied. It is observed that Dy doping could effectively improve the off current and the bias stress stability of the In2O3 devices due to the suppression of oxygen vacancies (VO). The optimized InDyO TFTs with 10 mol% Dy doping exhibit excellent electrical characteristics, including a μ of 7.60 cm2 V−1 s−1, high Ion/Ioff >108, small SS of 0.77 V/dec, Vth of 1.78 V, and excellent bias stress stability. Therefore, the InDyO TFTs grown from aqueous solution enable the development of environmentally friendly and large area electronics.

A high-performance solar-blind photodetector with a metal&ndash, semiconductor&ndash, metal structure was fabricated based on amorphous In-doped Ga2O3 thin films prepared at room temperature by radio frequency magnetron sputtering. The photodetector shows a high responsivity (18.06 A/W) at 235 nm with a fast rise time (4.9 &mu, s) and a rapid decay time (230 &mu, s). The detection range was broadened compared with an individual Ga2O3 photodetector because of In doping. In addition, the uneven In distribution at different areas in the film results in different resistances, which causes a quasi-Zener tunneling internal gain mechanism. The quasi-Zener tunneling internal gain mechanism has a positive impact on the fast response speed and high responsivity.

White light-emitting diode (LED) with effective energy conservation and long service life could be employed in numerous applications. In this study, the high-performance n-ZnO films were first prepared via pulsed laser deposition on p-GaN substrates and then the n-ZnO/p-GaN heterojunction LED was fabricated. This LED exhibits blue and yellow light emission, and their emission intensities can be tuned by adjustment of the fabrication parameters (e.g., oxygen pressure) and/or by introduction of a semi-insulating i-ZnO layer to form a p-GaN/i-ZnO/n-ZnO heterojunction. Thus, a facile approach has been proposed for the preparation of white LED.

Cubic MgZnO thin films were deposited on amorphous quartz substrate by PLD method. Effect of deposition pressure on preferential orientation and optical absorption characteristics of MgZnO thin films were studied. The preferred orientation of cubic MgZnO changed from (2 0 0) to (1 1 1) when deposition pressure increased, and absorption edges of which shift to longer wavelength direction because Mg content of MgZnO thin film decreased. Cubic MgZnO showed much better crystal quality and preferential orientation growth characteristics on proper crystal substrate, because on this substrate the preferred orientation of cubic MgZnO is accordance with that grown in free growth mode on amorphous substrate at special air pressure.

Black phosphorus (BP) has emerged as a promising two-dimensional (2D) material for next generation transistor applications due to its superior carrier transport properties. Among other issues, achieving reduced subthreshold swing and enhanced hole mobility simultaneously remains a challenge which requires careful optimization of the BP/gate oxide interface. Here, we report the realization of high performance BP transistors integrated with HfO2 high-k gate dielectric using a low temperature CMOS process. The fabricated devices were shown to demonstrate a near ideal subthreshold swing (SS) of ~69 mV/dec and a room temperature hole mobility of exceeding >400 cm2/Vs. These figure-of-merits are benchmarked to be the best-of-its-kind, which outperform previously reported BP transistors realized on traditional SiO2 gate dielectric. X-ray photoelectron spectroscopy (XPS) analysis further reveals the evidence of a more chemically stable BP when formed on HfO2 high-k as opposed to SiO2, which gives rise to a better interface quality that accounts for the SS and hole mobility improvement. These results unveil the potential of black phosphorus as an emerging channel material for future nanoelectronic device applications.

Zinc oxide (ZnO) films were deposited onto Si to form n-ZnO/p-Si heterojunctions. Under the illumination of by both ultraviolet (UV) light and sunlight, obvious photovoltaic behavior was observed. It was found that the conversion efficiency of the heterojunctions increased significantly with increasing thickness of the ZnO film, and the mechanism for light-harvesting in the heterojunctions is discussed. The results suggest that ZnO films may be helpful to increasing the harvesting of UV photons, thus decreasing the thermalization loss of UV energy in Si-based solar cells.

Lasing action is realized in a ZnO/GaN heterojunction by employing a MgO interlayer. The MgO layer can confine electrons in the ZnO layer, while holes can pass through the MgO layer and enter into the n-ZnO layer from the p-GaN layer. The threshold of the lasing action is as low as 0.8 mA.

In this paper, we have prepared Schottky type ZnO metal–semiconductor–metal (MSM) ultraviolet (UV) detector. The structural, electrical, and optical measurements were carried out. The detector exhibited a peak responsivity of 0.337 A/W at 360 nm and the dark current was about 1 nA under 3 V bias. An ultraviolet–visible rejection ratio was obtained about more than four orders of magnitude from the fabricated detector. The 10–90% rise and fall time were 20 ns and 250 ns, respectively. We proposed that the detector had shown a gain, which was attributed to the trapping of hole carriers at the semiconductor–metal interface.

Effect of a polarized P(VDF-TrFE) ferroelectric polymer gating on AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) was investigated. The P(VDF-TrFE) gating in the source/drain access regions of AlGaN/GaN MOS-HEMTs was positively polarized (i.e., partially positively charged hydrogen were aligned to the AlGaN surface) by an applied electric field, resulting in a shift-down of the conduction band at the AlGaN/GaN interface. This increases the 2-dimensional electron gas (2-DEG) density in the source/drain access region of the AlGaN/GaN heterostructure and thereby reduces the source/drain series resistance. Detailed material characterization of the P(VDF-TrFE) ferroelectric film was also carried out using the atomic force microscopy (AFM), X-ray Diffraction (XRD) and ferroelectric hysteresis loop measurement.

ZnO microrods (whiskers) were fabricated by a simple thermal oxidation method. The morphologies of the samples were detected by the scanning electron microscope, which showed the ZnO microrods were about 30 μm long with a diameter of 1–2 μm. In the photoluminescence (PL) spectra, only the exciton related emission bands in the ultraviolet region could be obtained at room temperature. And, a new emission band due to the exciton–exciton collision process was observed at the low energy side of the free exciton emission under the excitation intensity of 2.1 kW/cm2. This emission band increased nonlinearly. When the excitation intensity was increased above 16 kW/cm2 some fine structures could also be seen clearly in the PL spectra. These fine structures originated from the cavity modes of the Fabry–Perot etalon.

This paper reported AlGaN/GaN high electron mobility transistors (HEMTs) with low sub-threshold swing SS on free-standing GaN wafer. High quality AlGaN/GaN epi-layer has been grown by metal-organic chemical vapor deposition (MOCVD) on free-standing GaN, small full-width hall maximum (FWHM) of 42.9 arcsec for (0002) GaN XRD peaks and ultralow dislocation density (∼104-105 cm-2) were obtained. Due to these extremely high quality material properties, the fabricated AlGaN/GaN HEMTs achieve a low SS (∼60 mV/decade), low hysteresis of 54 mV, and high peak electron mobility μeff of ∼1456 cm2V-1s-1. Systematic study of materials properties and device characteristics exhibits that GaN-on-GaN AlGaN/GaN HEMTs are promising candidate for next generation high power device applications.

Wurtzite (Mg0.40Zn0.60O) thin films have been grown on quartz substrates by using the radio frequency magnetron sputtering technique, and a metal−semiconductor−metal Schottky barrier photodetector has been fabricated from these films. The photodetector exhibits a peak responsivity at 276 nm and a very sharp cutoff wavelength at 295 nm corresponding to the absorption edge of the Mg0.40Zn0.60O thin film. At 2 V bias, the detectivity of the photodetector is 1.1 × 1012 (cm Hz1/2)/W at 276 nm, and the ultraviolet-to-visible rejection ratio [R(276 nm)/R(400 nm)] is about 4 orders of magnitude. The photodetector also exhibits a very low dark current of about 100 pA at 2 V bias.

The energy band alignment between ZnO and multilayer (ML)-MoS2 was characterized using high-resolution x-ray photoelectron spectroscopy. The ZnO film was deposited using an atomic layer deposition tool, and ML-MoS2 was grown by chemical vapor deposition. A valence band offset (VBO) of 3.32 eV and a conduction band offset (CBO) of 1.12 eV were obtained for the ZnO/ML-MoS2 interface without any treatment. With CHF3 plasma treatment, a VBO and a CBO across the ZnO/ML-MoS2 interface were found to be 3.54 eV and 1.34 eV, respectively. With the CHF3 plasma treatment, the band alignment of the ZnO/ML-MoS2 interface has been changed from type II or staggered band alignment to type III or misaligned one, which favors the electron-hole pair separation. The band alignment difference is believed to be dominated by the down-shift in the core level of Zn 2p or the interface dipoles, which is caused by the interfacial layer rich in F.