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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.

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.

Layered SnSe2 have much attention due to their potential novel applications in electronic devices areas, such as photo-transistors, solar cells and memory devices. We investigate the thermal properties of few layer SnSe2 with capping of Al2O3 layer using the temperature and power-dependent Raman spectroscopy. The first order temperature coefficient of A1g modes of SnSe2 layers on a SiO2/Si substrate was found to be −0.01757 cm−1/K, which is much higher than the corresponding value −0.01270 cm−1/K of SnSe2 with Al2O3 layer. The difference in temperature coefficients is attributed to compressive stress introduced by the Al2O3 stress layer. Meanwhile, the Al2O3 layer significantly increases the thermal conductivity to 3.102 W/mK, which is larger than that of the SnSe2 films without Al2O3 (∼2.378 W/mK). The first principle calculation using CASTP demonstrated that this improvement of thermal conductivity is attributed to the compressive strain. This work suggests an effective way to improve the performances of SnSe2 based devices, and also need to understand the vibrational properties and electron-phonon interactions at the interface of Al2O3 and SnSe2 layers.

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.

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.

The effect of oxygen pressure on deposition orientation and the UV response characteristics of the β-Ga2O3 thin film by the Pulse Laser Deposition (PLD) method were studied. The β-Ga2O3 thin film deposited mainly along ( 2 ¯ 01 ) orientation at 0.5 Pa oxygen pressure, however it deposited more along (400) orientation when the oxygen pressure increased from 0.5 Pa to 2 Pa. The decrease in the migration energy of reactive Ga and O atoms from Ga2O3 target at higher oxygen pressure is the main reason for the change in the orientation of the β-Ga2O3 thin film. The β-Ga2O3 thin film that was constituted mainly by ( 2 ¯ 01 ) and (400) orientations β-Ga2O3 was made at 2 Pa, where the band gap of the β-Ga2O3 thin film is wider than the ( 2 ¯ 01 ) orientation ones deposited at smaller oxygen pressure, and the maximum response of the β-Ga2O3 thin film shifted considerably from 255 nm to 240 nm compared with ( 2 ¯ 01 ) orientation β-Ga2O3 thin film. Because the Idark of the UV detector based on the mix-orientation β-Ga2O3 thin film is just 2.53 nA under 25 V bias voltage, which is much smaller than that of the ( 2 ¯ 01 ) β-Ga2O3 based detector, the Iuv/Idark of the mix-orientation β-Ga2O3–based detector reached 2500 at 25 V bias voltage. This value is much higher than the ( 2 ¯ 01 ) β-Ga2O3–based detector both in our experiments and in reported results. Wider band gap (400) β-Ga2O3 and relative higher density of boundaries at the interfaces between (400) and ( 2 ¯ 01 ) β-Ga2O3 are the main reasons for the smaller Idark and the higher Iuv/Idark of the β-Ga2O3 UV detector deposited at 2 Pa. The β-Ga2O3 thin film deposited along multiple orientations at oxygen pressure over 2Pa, the UV response, and Iuv of the β-Ga2O3 thin films deposited at higher oxygen pressure was much smaller than the one deposited at 2 Pa, and the Iuv/Idark was also much smaller. In addition, the UV β-Ga2O3 detector that composed of both (400) and ( 2 ¯ 01 ) β-Ga2O3 showed similar response time (0.8 us) and much smaller decay time (80 us) compared with the ( 2 ¯ 01 ) β-Ga2O3–based detector, which was also much faster than the reported results. Therefore, when appropriate numbers of (400) β-Ga2O3 were mixed into the ( 2 ¯ 01 ) β-Ga2O3 thin film, the mix-orientation β-Ga2O3–based UV detector showed a much lower noise level, much higher signal/noise ratio, and much faster decay speed at shorter wavelength UV light compared with a single ( 2 ¯ 01 ) β-Ga2O3–based based UV detector.

Two-dimensional thin layers of indium selenide (InSe) have attracted much attention due to their potential applications in optoelectronics as highly responsive photo-detectors and field-effect transistors. In the present work, we explore thermal properties of InSe thin layers on a high-k substrate with a thin SiO2 passivation layer using temperature and power dependent Raman spectroscopy. The first order temperature coefficients for in-plane (E12g) and out-of-plane (A21g) modes of InSe few-layers on a Al2O3 substrate were found to be −0.00507 and −0.00310 cm−1/K, respectively, which are much smaller than the corresponding values −0.00612 and −0.00528 cm−1/K of similarly prepared sample on SiO2 substrate. The difference in temperature coefficients is attributed to compressive strain introduced by the Al2O3. Further, the average thermal conductivity of a 4 nm thin InSe layer on the Al2O3 substrate at room temperature was found to be ∼53.4 W/m-K, which is significantly larger than those of InSe layers prepared on SiO2 substrate (∼28.7 W/m-K). The existed interface charges between the Al2O3 and InSe layers cause the observed improvement of thermal conductivity by electron-phonon interactions.

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.

High-resolution x -ray photoelectron spectroscopy (XPS) was employed to characterize the energy band alignment between TiO 2 /multilayer (ML)-MoS 2 . The TiO 2 film and ML-MoS 2 film was grown by an atomic layer deposition (ALD) and chemical vapor deposition (CVD), respectively. The effect of CHF 3 plasma treatment on the band alignment between TiO 2 /ML-MoS 2 was evaluated. It was found that the valence band offset (VBO) and a conduction band offset (CBO) of TiO 2 /ML-MoS 2 interface was changed from 2.28 eV to 2.51 eV, and from 0.28 eV to 0.51 eV, respectively for the sample with CHF 3 plasma treatment. With the CHF 3 plasma treatment, the down-shift of Mo 3d core level binding energy results in a bend-up of energy potential on the MoS 2 side, leading to 0.23 eV ΔE C difference between the control and the sample with CHF 3 plasma treatment, which is caused by the interfacial layer in rich of F element. The physics details of the band alignment at TiO 2 /ML-MoS 2 interface will provide a guide for the MoS 2 based electronic device design.

Present work proposes the insight towards synthesis of flower-like vanadium oxide hierarchical nanostructures (V2O5 HNs) through a simple and template-free hydrothermal method and their utilization as a potential xylene gas sensing materials. XRD and XPS analysis supports to the configuration of highly crystalline orthorhombic phase of V2O5. Surface morphologies of V2O5 were controlled through varying the reaction times during hydrothermal synthesis. SEM and TEM studies undoubtedly corroborates that the flower-like V2O5 HNs (3–5 μm in diameters) are composed of large number of nanosheet- and nanoneedle-type structures. BET and BJH analysis supports to the mesoporous character of V2O5 HNs with specific surface area of 19.5291 m2/g. Gas sensing studies on as-fabricated V2O5 HNs sensors were performed towards a various target gases, temperatures, and varying concentrations thoroughly and described. Gas sensing studies demonstrate that the flower-like V2O5 HNs sensors are selective and effective towards xylene @300 °C. Among various V2O5 HNs sensors, the sensor based on V2O5-3 exhibits maximum response of 3.03 to 500 ppm xylene together with good response repeatability and long term stability (towards 100 ppm, Ra/Rg = 2.20) @300 °C. Finally, the selective detection of xylene using as-grown flower-like V2O5 HNs can cover the road in the direction of the development of sensing systems for the acute detection and monitoring of toxic xylene.

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.