Ma Honglei

Optical and electronic properties of transparent conducting ZnO and ZnO:Al films prepared by evaporating method

Abstract Undoped and Aluminium-doped Zinc oxide films have been prepared by thermal evaporation of zinc acetate (Zn(CH3COO)2·2H2O] and aluminium chloride (AlCl3) onto a heated glass substrate. The structural, optical and electrical properties of the films have been studied. The effects of heat treatment for the as-deposited films in air and vacuum are investigated. Over 80% transmittance films with conductivity as low as 2×10 −3 Ω cm can be produced by controlling the deposition parameters. The electron carrier densities are in the range 0.2–7×10 19 cm−3 with mobilities of 22–58 cm2/Vs.

Thermal Decomposition Behaviour of Zn3N2 Powder

Thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) are employed to investigate the thermal decomposition behaviour of zinc nitride powder, which indicated that the thermal oxidation of zinc nitride powder in air follows the two-step reaction model. When the temperature is between 200 and 500 degrees C, compact ZnO or ZnxOyNz layers in the surface of zinc nitride powder will begin to form, and prevent the interior of zinc nitride powder from the thermal oxidation. When the temperature is higher than 500 degrees C, fast thermal oxidation occurs in the interior of zinc nitride powder. Over 750 degrees C, all the zinc nitride will turn into zinc oxide. The x-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) of the zinc nitride powder annealed at different temperature in air are consistent with the two-step reaction model.

Structure Properties of MgxZn1−xO Films Deposited at Low Temperature

MgxZn1−xO films (x = 0.23) have been prepared on silicon substrates by radio-frequency magnetron sputtering at 80 degrees C. The structure properties of MgxZn1−xO films are studied using x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy and Raman spectra. The analysis of XRD and HRTEM indicates that the MgxZn1−xO films have hexagonal wurtzite single-phase structures and a preferred orientation with the c axis perpendicular to the substrates. Raman spectra of ZnO and MgxZn1−xO films reveal that the MgxZn1−xO films have not only the hexagonal wurtzite structure but also higher crystalline quality than ZnO films.

Effect of high temperature annealing on strain and band gap of GaN nanoparticles

Black-coloured GaN nanoparticles with an average grain size of 50 nm have been obtained by annealing GaN nanoparticles under flowing nitrogen at 1200 °C for 30 min. XRD measurement result indicates an increase in the lattice parameter of the GaN nanoparticles annealed at 1200 °C, and HRTEM image shows that the increase cannot be ascribed to other ions in the interstitial positions. If the as-synthesised GaN nanoparticles at 950 °C are regarded as standard, the thermal expansion changes nonlinearly with temperature and is anisotropic; the expansion below 1000 °C is smaller than that above 1000 °C. This study provides an experimental demonstration for selecting the proper annealing temperature of GaN. In addition, a large blueshift in optical bandgap of the annealed GaN nanoparticles at 1200 °C is observed, which can be ascribed to the dominant transitions from the C(Γ7) with the peak energy at 3.532 eV.

Preparation and Properties of GaN Films on GaAs Substrates

High-quality gallium nitride (GaN) films were prepared on Si(111) substrates by sputtering post-an nealing-reaction technique. XRD, XPS, and SEM measurement results indicate that polycrystalline GaN with hexagonal structure was successfully prepared. Intense room-temperature photoluminescence that peaked at 354 nm of the films is observed. The bandgap of these films has a blueshift with respect to bulk GaN.

A new mechanism of light-induced reversible changes in a-Si:H p-i-n solar cells

Abstract Based on analysis of the experimental results of photoinduced changes and of transient photoresponse, a new mechanism for light-induced changes in a-Si:H p-i-n solar cells is suggested. This mechanism takes into account both the reversible changes of dangling bond density and the activation energy of annealing, commonly ranging from 1 eV to 1.5 eV. It is suggested that there is a stable density of T 3 + and of T 3 − in the annealed state, and that the transition T 3 + + T 3 − → 2T 3 0 is induced by light and the reversal 2T 3 0 → T 3 + + T 3 − by annealing.

Preparation and Characterization of GaN Nanowires

GaN Nanowires were prepared by the post-nitridation technique. The morphology and structure of GaN nanowires are investigated by transmission-electron microscopy and scanning electron microscopy. A strong blue photoluminescence is observed for room-temperature measurement, which attributes to electron transition from DX centre to valence band.

A low-energy photoluminescence peak in A-Si: H films

A 0.65-0.70eV luminescence peak in a-Si: H films after illumination is reported. It is found that exposure to light decreases total integrated intensity of luminescence and also produces two luminescence peaks, one is in the range 0.80-0.90eV, and the other is in 0.65-0.70eV. The former disapears by annealing at 190°C, but the latter can not be removed. Similar luminescence peaks are observed in a-Si: H films prepared under higher RF power without illumination.

Some Propreties of B-Doped Silicon Films

Some results of B-doped silicon films prepared by low pressure chemical vapor deposition (LPCVD) are reported, (l) The flow rate of gases is one of the important factors which affect the properties of the films, and there is an optimal flow rate. (2) The direct current conductivity (σ) of films depends on the growth temperature. X-ray diffraction and scanning-electron-microscope expertmeats show that the B-doped silicon films prepared at about 635°c have possibly amorphous and microcrystal structures, and σ is about 102 Ω-1 cm-1 under room temperature; And that the diffraction peaks in (lll) (220) are found for the films prepared at about and above 670°c, but not for that below 655°c. (3) The activation energy of both are 0.026ev and o.23ev respectively. (4) No hydrogen peaks are found from Infrared Absorption experiment.