Gu Shulin

Optical and Magnetic Properties of Fe-Doped GaN Diluted Magnetic Semiconductors Prepared by MOCVD Method

Fe-doped GaN thin films are grown on c-sapphires by metal organic chemical vapour deposition method (MOCVD). Crystalline quality and phase purity are characterized by x-ray diffraction and Raman scattering measurements. There are no detectable second phases formed during growth and no significant degradation in crystalline quality as Fe ions are doped. Fe-related optical transitions are observed in photoluminescence spectra. Magnetic measurements reveal that the films show room-temperature ferromagnetic behaviour. The ferromagnetism may originate from carrier-mediated Fe-doped GaN diluted magnetic semiconductors or nanoscale iron clusters and Fe-N compounds which we have not detected.

Effects of interface traps in silicon-quantum-dots-based memory structures

Abstract Effects of interface traps in silicon-quantum-dots(Si-QDs) based memory structures have been investigated using capacitance–voltage measurement. The observations demonstrate that both the interface traps at Si-QDs and the interface states at SiO 2 /Si-substrate have strong influences on the charge storage characteristics. The observed long-term charge retention behavior is analyzed in terms of direct charge-tunneling from deep trapping centers at Si-QDs to the interface states at SiO 2 /Si-substrate, considering three-dimensional quantum confinement and Coulomb charging effects.

High-quality ZnO growth, doping, and polarization effect

The authors have reported their recent progress in the research field of ZnO materials as well as the corresponding global advance. Recent results regarding (1) the development of high-quality epitaxy techniques, (2) the defect physics and the Te/N co-doping mechanism for p-type conduction, and (3) the design, realization, and properties of the ZnMgO/ZnO hetero-structures have been shown and discussed. A complete technology of the growth of high-quality ZnO epi-films and nano-crystals has been developed. The co-doping of N plus an iso-valent element to oxygen has been found to be the most hopeful path to overcome the notorious p-type hurdle. High mobility electrons have been observed in low-dimensional structures utilizing the polarization of ZnMgO and ZnO. Very different properties as well as new physics of the electrons in 2DEG and 3DES have been found as compared to the electrons in the bulk.

Roles of V/III ratio and mixture degree in GaN growth: CFD and MD simulation study

To understand the mechanism of Gallium nitride (GaN) film growth is of great importance for their potential applications. In this paper, we investigate the growth behavior of the GaN film by combining computational fluid dynamics (CFD) and molecular dynamics (MD) simulations. Both of the simulations show that V/III mixture degree can have important impacts on the deposition behavior, and it is found that the more uniform the mixture is, the better the growth is. Besides, by using MD simulations, we illustrate the whole process of the GaN growth. Furthermore, we also find that the V/III ratio can affect the final roughness of the GaN film. When the V/III ratio is high, the surface of final GaN film is smooth. The present study provides insights into GaN growth from the macroscopic and microscopic views, which may provide some suggestions on better experimental GaN preparation.

Synthesis of [100] Wurtzite InN Nanowires and [011] Zinc-Blende InN Nanorods

One-dimensional wurtzite InN nanowires and zincblende InN nanorods are prepared by chemical vapour deposition (CVD) method on natural cleavage plane (110) of GaAs. The growth direction of InN nanowires is [100], with wurtzite structure. The stable crystal structure of InN is wurtzite (w-InN), zincblende structure (z-InN) is only reported for 2D InN crystals before. However, in this work, the zincblende InN nanorods [011] are synthesized and characterized. The SEM and TEM images show that every nanorod shapes a conical tip, which can be explained by the anisotropy of growth process and the theory of Ehrlich?Schwoebel barrier.

Interfacial Properties of AlN/Si (111) Grown by Metal-Organic Chemical Vapour Deposition

We have studied the interfacial structures of AlN/Si (111) grown by metal-organic chemical vapour deposition. X-ray photoelectron spectroscopy and Auger electron spectroscopy were used to analyse the components and chemical structures of AlN/Si (111). The results indicated that a mix-crystal transition region, approximately 12nm, was present between the AlN film and the Si substrate and it was composed of AlN and Si3N4. After analysis we found that the existence of Si3N4 could not be avoided in the AlN/Si (111) interface because of strong diffusion at 1070°C. Even in AlN layer Si-N bonds, Si-Si bonds can be found.

Simulation and Suppression of the Gas Phase Pre-reaction in Metal-Organic Chemical Vapor Deposition of ZnO

The reaction mechanism and simulations of the metal-organic chemical vapor deposition reactor for ZnO film growth are presented, indicating the temperature of the reaction species. The gas phase pre-reaction can be modulated by several factors or conditions. Simulations verify the relationships between temperature and pyrolysis of precursors, and further reveal that the substrate temperature and flow rate of cooling water have great impacts on the temperature distribution. The experimental results agree with the simulations.

Crystal Tilts in Epitaxially Laterally Overgrown GaN Films Determined by Four-Circle X-Ray Diffraction

Crystal tilts in epitaxially laterally overgrown (ELO) GaN films via hydride vapour phase epitaxy (HVPE) on sapphire substrates have been investigated by using the four-circle x-ray diffraction method. Three diffraction peaks corresponding to the (0002) reflection of vertically epitaxial and tilted GaN domains are observable in the x-ray rocking curve. The angle separations Δω between the main peak and two lobes change with the azimuth angle . The dependence of Δω on and the crystal tilt angle θ has been calculated based on the standard kinetic x-ray diffraction model. The crystal tilt angle of a typical HVPE ELO GaN sample has been determined to be 2.379°.

Preparation of AlGaN/GaN Heterostructures on Sapphire Using Light Radiation Heating Metal-Organic Chemical Vapor Deposition at Low Pressure

AlGaN/GaN heterostructures on sapphire substrate were fabricated by using light radiation heating metalorganic chemical vapor deposition. Photoluminescence excitation spectra show that there are two abrupt slopes corresponding to the absorption edges of AlGaN and GaN, respectively. X-ray diffraction spectra clearly exhibit the GaN (0002), (0004), and AlGaN (0002), (0004) diffraction peaks, and no diffraction peak other than those from the GaN {0001} and AlGaN {0001} planes is found. Reciprocal space mapping indicates that there is no tilt between the AlGaN layer and the GaN layer. All results also indicate that the sample is of sound quality and the Al composition in the AlGaN layer is of high uniformity.

In-Plane Optical Anisotropy of a-Plane GaN Film on r-Plane Sapphire Grown by Metal Organic Chemical vapour Deposition

The in-plane optical anisotropic properties of the non-polar a-plane GaN films grown by metal organic chemical vapour deposition are investigated by using polarised photoluminescence (PL), optical transmission and Raman scattering measurements. Through polarised PL and transmission spectra, the in-plane optical anisotropic properties of a-plane GaN film are found, which are attributed to the topmost valance band (at Γ point) split into three sub-bands under anisotropic strain. The PL spectra also exhibit that the light hole band moves up more rapidly than the spin-orbit crystal-field spilt-off hole band with the increasing in-plane anisotropic compressive strain. Raman scattering spectra under different configurations further indicate the in-plane anisotropy and the hexagonal crystalline structure of these a-plane GaN films.