Li Qing-Shan

White Light Emission from the Composite System of ZnO/Porous Si

We report that the composites of ZnO/porous Si (PS) can exhibit intensively white photoluminescence (PL) under proper excitation wavelength. The PS sample is formed by electrochemical anodization of n-type (111) silicon. ZnO films are then deposited on the PS surface by pulsed laser deposition (PLD). ZnO is transparent in the visible region, so the red PL from PS can be transmitted through the ZnO films. White PL from the ZnO layer on PS can be obtained, which consists of blue-green emission from ZnO and red emission from PS. The x-ray diffraction (XRD) pattern shows that the ZnO films deposited on PS surface are non-crystalline. Due to the roughness of the PS surface, some cracks appear in the ZnO films, which could be seen from the scanning electron microscopy (SEM) images.

Optical and Electrical Properties Evolution of Diamond-Like Carbon Thin Films with Deposition Temperature

Optical and electrical properties of diamond-like carbon (DLC) films deposited by pulsed laser ablation of graphite target at different substrate temperatures are reported. By varying the deposition temperature from 400 to 25° C, the film optical transparency and electrical resistivity increase severely. Most importantly, the transparency and resistivity properties of the DLC films can be tailored to approaching diamond by adjusting the deposition temperature, which is critical to many applications. DLC films deposited at low temperatures show excellent optical transmittance and high resistivity. Over the same temperature regime an increase of the sp3 bonded C content is observed using visible Raman spectroscopy, which is responsible for the enhanced transparency and resistivity properties.

Structural, Optical and Electrical Properties of ZnS/Porous Silicon Heterostructures

ZnS films are deposited by pulsed laser deposition on porous silicon (PS) substrates formed by electrochemical anodization of p-type (100) silicon wafer. Scanning electron microscope images reveal that the surface of ZnS films is unsmoothed, and there are some cracks in the ZnS films due to the roughness of the PS surface. The x-ray diffraction patterns show that the ZnS films on PS surface are grown in preferring orientation along cubic phase β-ZnS (111) direction. White light emission is obtained by combining the blue-green emission from ZnS films with the orange–red emission from PS layers. Based on the I–V characteristic, the ZnS/PS heterojunction exhibits the rectifying junction behaviour, and an ideality factor n is calculated to be 77 from the I–V plot.

Optical absorption and photoluminescence of unhydrogenated amorphous carbon films

Abstract Unhydrogenated amorphous carbon (a-C) films were prepared by a laser beam technique. Optical absorption, photoluminescence (PL) and the dependence of PL spectra on the incident laser intensity were studied. The optical gap, peak energy of the PL spectrum and band tail width change with preparation bias voltage. At room temperature PL spectra exhibit a superlinear behaviour at lower incident intensity, linear behaviour at higher intensities, and a large blue shift of peak energy with increasing excitation intensity. These results can be qualitatively explained in the light of the distribution of gap states and tail state population.

Effects of Substrate Temperature and Nitrogen Pressure on Growth of AlN Films by Pulsed Laser Deposition

Highly oriented aluminium nitride (AlN) films are grown on p-Si (100) substrates by pulsed laser deposition, and their characteristics of structure and composition are studied by x-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. The results show that the deposited films exhibit good crystalline properties with a sharp x-ray diffraction peak at 2θ = 33.15° corresponding to AlN h100 crystalline orientation. The influences of substrate temperature and ambient nitrogen (N2) pressure on the crystallinity of AlN films are remarkable. At room temperature, when the ambient N2 pressure arises from 5×10−6 Pa to 5 Pa, the crystallinity of the film becomes better. When the substrate temperature is 600°C, the film has the best crystallinity at 0.05 Pa. Furthermore, the effects of substrate temperature and ambient N2 pressure on the combination of Al-N bonds and surface morphology of AlN films are also studied.

Improvement in electroluminescence performance of n-ZnO/Ga2O3/p-GaN heterojunction light-emitting diodes

n-ZnO/p-GaN heterojunction light-emitting diodes with and without a Ga2O3 interlayer are fabricated. The electroluminescence (EL) spectrum of the n-ZnO/p-GaN displays a single blue emission at 430 nm originating from GaN, while the n-ZnO/Ga2O3/p-GaN exhibits a broad emission peak from ultraviolet to visible. The broadened EL spectra of n-ZnO/Ga2O3/p-GaN are probably ascribed to the radiative recombination in both the p-GaN and n-ZnO, due to the larger electron barrier (ΔEC = 1.85 eV) at n-ZnO/Ga2O3 interface and the much smaller hole barrier (ΔEV = 0.20 eV) at Ga2O3/p-GaN interface.