Wancheng Li

Near infrared electroluminescence from n-InN/p-GaN light-emitting diodes

Undoped InN thin film was grown on p-GaN/Al2O3 (0001) template by molecular beam epitaxy. Near-infrared (NIR) electroluminescence (EL) that overlapped the optical communication wavelength range was realized using the n-InN/p-GaN heterojunction structure. The light emitting diode showed typical rectification characteristics with a turn-on voltage of around 0.8 V. A dominant narrow NIR emission peak was achieved from the InN side under applied forward bias. By comparing with the photoluminescence spectrum, the EL emission peak at 1573 nm was attributed to the band-edge emission of the InN film.

Cu related doublets green band emission in ZnO:Cu thin films

Cu-doped ZnO (ZnO:Cu) thin films were grown on Si (111) substrate by low-pressure metal-organic chemical vapor deposition equipment. The crystal structures and optical properties of as-grown sample were examined. X-ray diffraction patterns indicated a lattice relaxation after the Cu doping. The incorporation of Cu atoms into ZnO film and its existence in a bivalent state were demonstrated by x-ray photoelectron spectroscopy measurements. Low-temperature photoluminescence was carried out at temperature of 11.4 K for both unintentionally doped and Cu-doped ZnO films. A characteristic green-luminescence with fine structure consisted of doublets emission peak was observed, which was believed to be associated with Cu doping. A theoretical model based on hydrogen analog has been proposed to explain this phenomenon. It provides new information about the detailed role of Cu in ZnO thin films.

Near infrared electroluminescence from n-InN/p-NiO heterojunction light-emitting diode

The n-InN/p-NiO heterojunction was fabricated by growing an n-type InN film on a c-plane sapphire substrate by plasma-assisted molecular beam epitaxy (PAMBE) and then depositing a p-type NiO film on the InN film by radio frequency (RF) magnetron sputtering. The heterojunction exhibited typical rectification characteristic with a turn-on voltage of ∼1.1 V. A dominant near infrared (NIR) emission was detected from the heterojunction under forward bias. The intensity of the emission increased significantly as the injection current increased from 2 to 10 mA. The NIR emission peaking around 1565 nm was ascribed to the band-edge emission of InN layer based on the photoluminescence spectrum and band diagram of the heterojunction.

Band alignment of InN/6H-SiC heterojunction determined by x-ray photoelectron spectroscopy

The valence band offset (VBO) of InN/6H-SiC heterojunction has been directly measured by x-ray photoelectron spectroscopy. The VBO is determined to be −0.10 ± 0.23 eV and the conduction band offset is deduced to be −2.47 ± 0.23 eV, indicating that the heterojunction has a type-II band alignment. The accurate determination of the valence and conduction band offsets is important for applications and analysis of InN/6H-SiC optoelectronic devices.

Green electroluminescence from ZnO/n-InP heterostructure fabricated by metalorganic chemical vapour deposition

Vertically aligned ZnO films were deposited on n-InP by metalorganic chemical vapour deposition. X-ray diffraction, field emission scanning electron microscopy and photoluminescence measurements demonstrated that the ZnO films had good quality. By evaporating AuZn electrodes on both ZnO and InP surfaces, a ZnO-based light emitting device was fabricated. Under forward voltage, weak green emissions can be observed in darkness.

Excellent optical quality versus strong grain boundary effect in a double-layer ZnO structure

ZnO samples with a double-layer structure and top nanorod arrays on the bottom film layer were grown by metal-organic chemical vapor deposition at a temperature range from 340 to 400 °C. The ZnO nanorods show excellent optical quality and no obvious defect related emission can be detected below 40 K except for I6 line and the surface bound exciton emission. The free exciton emission and its phonon replicas dominate the near band edge emission between 40 and 295 K. For the film layer, the temperature-dependent Hall measurements showed that the conduction region is degenerate. In the conduction region, the carrier mobility is mainly limited by the grain boundary effect, which can be weakened by thermal annealing. The conduction mechanism in this region before and after annealing can be fitted by a uniform and a non-uniform conduction model, respectively. The results indicate that grain boundary effects strongly limit the mobility and consume large amounts of carriers by the trap states. Furthermore, we propose a qualitative model to explain the expansion of the conduction regions by annealing. It reveals a mechanism for the improvement of electrical properties of polycrystalline thin films by annealing treatments.

Photoemission spectroscopy study of oxygen spectrum and the chemical failure process of Alq3-based light-emitting devices

Tris (8-hydroxyquinolino) aluminum (Alq3) films and their chemical failure process are investigated using x-ray photoelectron spectroscopy. We make sure that the O 1s spectrum of the pristine Alq3 only has one component which is in contrast to the current controversy on this issue. Our experiments further indicate that the chemical failure process of Alq3 holds the critical role to understand this problem. The chemical failure process also shows the organic carbon contamination and the replacement reaction between Alq3 and water, ultimately resulted in the failure of the device. These fundamental results provide a basis understanding for future development of Alq3-based light emitting devices.

Key Points in Establishing a Model of Mouse Liver Transplantation

The explosion of interest in research into the mouse genome and immune system has meant that the mouse orthotopic liver transplantation (MOLT) model has become a popular means of studying transplantation immunity, organ preservation, ischemia-reperfusion injury, and surgical techniques, among others. Although numerous modifications and refinements of surgical techniques have simplified the operation, the relatively short duration of postoperative survival after MOLT remains an obstacle to longer-term follow-up studies. Here, we summarize the scientific basis of MOLT and our experience improving and refining the model in six key areas: anesthesia, operative technique, perfusion and preservation of the liver, cuff technique, anhepatic time, and the value of rearterialization for the liver graft. We also compare the characteristics of different surgical techniques, and give recommendations for the best means of tailoring technique to the objectives of a study. In doing so, we aim to assist other investigators in establishing and perfecting the MOLT model in their routine research practice.

A new method of restraining the Fabry-Perot resonance

In the paper, we present a new method of restraining the Fabry–Perot resonance. The method is to combine dip angle with taper angle in the structure of the device and avoids the process of antireflection coatings. The experimental results show that restraining effect is apparent. A high threshold current has been obtained for the sample with both dip angle and taper angle structure. It provides a new method to make traveling-wave optical amplifiers.