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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.

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.

We present a low-temperature optical study of the large-area monolayer WS2 grown by chemical vapor deposition (CVD). Power-dependent photoluminescence (PL) measurements were conducted, and temperature-dependent PL spectra were measured in the range of 3 to 300 K. With the comparative PL bands obtained, a stronger trion emission in the edge region was detected to be the key difference. Sulfur vacancies (SVs) were observed to increase in density along the growth direction and found to be the main source of the large population of local charge carriers. The monolayer WS2 exhibited an upper bound for the trion binding energy of 18 meV in the edge region.

Thin films of p-type ZnO:N have been obtained by thermally oxidizing zinc oxynitride films prepared by plasma enhanced chemical vapour deposition (PECVD). The p-type ZnO:N thin film with a hole concentration of 2.7 × 1016 cm−3 was obtained after an annealing process was conducted at 600 °C. A conductivity transition from n-type to p-type was observed, which was systematically researched via structural and compositional analyses. In terms of these analyses, it helped to better understand the properties and behaviour of nitrogen in ZnO. First, nitrogen was incorporated into ZnO films during the growth process to occupy oxygen positions, and also partly compensated some donors induced from non-stoichiometric (ZnO1–x) composition. Second, the amount of activated nitrogen gradually increased in an oxidizing atmosphere and exceeded those donor states to realize an effective compensation, yielding p-type conductivity during the course of thermal oxidation.

Photoluminescence (PL) properties of ZnO films grown on (001) InP substrates by thermal oxidization of metallic Zn films, in which oxygen vacancies and interstitial Zn ions are compensated by P ions diffusing from (001) InP substrates, are investigated. X-ray diffraction spectra indicate that P ions have diffused into the Zn films and chemically combined with Zn ions to form Zn3P2. Intense free exciton emission dominates the PL spectra of ZnO films with very weak deep-level emission. Low-temperature PL spectra at 79 K are dominated by neutral-donor bound exciton emission at 3.299 eV (I4) with a linewidth of 17.3 meV and neutral-acceptor bound exciton emission at 3.264 eV. The free exciton emission increases with increasing temperature and eventually dominates the emission spectrum for temperature higher than 170 K. Furthermore, the visible emission around 2.3 eV correlated with oxygen deficiencies and interstitial Zn defects was quenched to a remarkable degree by P diffusing from InP substrates.

We report the fabrication and characterization of high voltage AlGaN/GaN metal–oxide–semiconductor high-electron mobility transistors (MOSHEMTs) with selectively regrown In0.14Ga0.86N contact using a CMOS compatible gold-free process. Device with the regrown InGaN contact with a gate-to-drain spacing LGD of 5 µm achieves an off-state breakdown voltage VBR of 800 V and on-state resistance Ron of 2 mΩ·cm2. The VBR achieved in this work is higher than those of gold-free GaN MOSHEMTs with gate-to-drain spacing LGD below 10 µm.

Heavily doped Ga-doped ZnO (resistivity ?8???10?4???cm and optical transmittance 96%) were fabricated by radio frequency magnetron sputtering. Post-growth annealing studies in H2?Ar and pure Ar atmospheres were conducted. No noticeable thermal-induced change in the Ga depth profile or in the Ga chemical state was found in both atmospheres up to 600??C. The Burstein?Moss effect was exhibited in the effective optical band gap, and the cathodoluminescence (CL) photon energy of the near band edge emission. CL emission related to VZn persisted after the 600??C annealing. The thermal evolutions of the carrier concentrations were nearly identical for both annealing atmospheres. The carrier mobility increased upon annealing in H2/Ar and remained effectively unchanged in pure Ar. The observed changes in carrier concentration and mobility were tentatively associated with VZn, or other compensating defects, which have concentrations as high as 1019?1020?cm?3.

Zinc oxide (ZnO) films have been prepared on sapphire substrates by molecular beam epitaxy. It is found that the electron concentration of the films decreases, while the mobility increases with increasing the film thickness. Temperature-dependent Hall measurement reveals the existence of a degenerate layer at the ZnO/sapphire interface, which will increase the electron concentration and decrease the mobility in the ZnO film. By using a two-layer conduction model, the electron concentration and mobility of the film excluding the influence of the degenerate layer have been determined. A fitting to the corrected electron concentration of the ZnO film yields an activation energy of about 31 meV for the residual donors.

Nitrogen doped zinc oxide (ZnO) films have been prepared by molecular beam epitaxy. The as-grown samples show n-type conduction, but they convert to p-type after being annealed in O2 atmosphere. X-ray photoelectron spectroscopy reveals that the conversion is mainly caused by the escaping of substituted N molecule (N2)O donors from the films, and photoluminescence spectroscopy confirms the extraction of (N2)O. The work shown in this paper reveals experimentally that the main compensation source in nitrogen doped ZnO is (N2)O donors instead of intrinsic donors or background impurities, and annealing in oxygen may be a promising route to p-ZnO.

Excitonic optical bistability with picosecond switching time in ZnSe-CdZnSe multiple quantum wells (MQWs) optical bistable device is investigated at room temperature for the first time. The result indicates that the threshold and contrast ratio for the optical bistability in ZnSe-CdZnSe MQWs optical bistable device are about 210 kW/cm2 and 2 : 1, respectively. On the basis of the excitonic nonlinear theories, excitonic absorption and excitonic emission under different excitation intensities in the ZnSe-CdZnSe MQWs obtained here, we attribute the major nonlinear mechanism for the optical bistability in ZnSe-CdZnSe MQWs optical bistable device to the phase space filling of excitonic states and excitonic band broadening due to exciton-exciton interactions.

We present a simple, but highly sensitive, method for obtaining both the sign and magnitude of the nonlinear refractive index and the nonlinear absorption coefficient as a function of wavelength. It is shown theoretically that these parameters can be easily obtained from the linear and nonlinear transmission spectra of the medium as well as the laser intensity distribution on the frequency. This technique is demonstrated for ZnSe-ZnS multiple quantum wells on transparent CaF2 substrate at 77 K.