H. Q. Ni

The effects of thermal annealing on ZnO thin films grown by pulsed laser deposition

ZnO thin films were grown on silicon (100) by pulsed laser deposition. Highly textured crystalline ZnO thin films can be grown at 600u2009°C. The films were then annealed at 600u2009°C in oxygen. The effects of annealing on chemical composition of the ZnO films were investigated by x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The XPS spectra indicate that water has been adsorbed and then dissociated into H and OH groups. The surface properties of ZnO were studied both by scanning tunneling microscopy and scanning tunneling spectroscopy (STS). A narrow potential well has been formed on the surface of the ZnO thin films due to high density of surface states and negatively biasing the ZnO thin films during STS measurement. The discrete energy levels can be measured by STS.

Investigation of Li-doped ferroelectric and piezoelectric ZnO films by electric force microscopy and Raman spectroscopy

We have grown Li-doped ZnO films on silicon (100) using the rf planar magnetron sputtering method. The surface charges induced piezoelectrically by defect and by polarization can be observed by electric force microscopy. The Li-doped ZnO films have been proven to be ferroelectric. The Raman spectra of ZnO and Li-doped ZnO films have been measured.

Room temperature synthesis of c-AlN thin films by nitrogen-ion-assisted pulsed laser deposition

Cubic aluminum nitride (c-AlN) thin films have been deposited at room temperature on silicon substrates by nitrogen-ion-assisted pulsed laser ablation of a hexagonal AlN target. The deposited thin films exhibit good crystal properties with sharp x-ray diffraction peaks. The influences of the nitrogen ion energy on the morphological, compositional, and electronic properties of the AlN thin films have been studied. The nitrogen ions can effectively promote the formation of Al–N bonds and improve the crystal properties of the deposited thin films. A nitrogen ion energy of 400 eV is proposed to deposit high quality c-AlN thin films.

Quasiparticle band structures of wurtzite and rock-salt ZnO

Band structures of both wurtzite and rock-salt ZnO were investigated using the ab initio pseudopotential method with both local density approximation (LDA) and GW approximation. The error in approximating 3d electrons as core electrons was investigated for both LDA and quasiparticle calculations. The differences between the band structures obtained by the GW approximation and LDA were explained. The quasiparticle band structures were compared with experimental results. The spin–orbit splitting was calculated for both wurtzite and rock-salt ZnO with the LDA. The density of states was investigated with the GW approximation.

Growth of crystalline ZnO thin films on silicon (100) and sapphire (0001) by pulsed laser deposition

Zinc oxide thin films have been grown on silicon (100) and sapphire (0001) substrates by pulsed laser deposition. The thin films deposited at different processing parameters were evaluated by x-ray diffraction, Raman spectroscopy, and atomic force microscopy (AFM). The influences of substrate temperature and laser fluence on the properties of the deposited thin films were studied. The full width at half maximum of (0002) x-ray diffraction lines of the films deposited on silicon and sapphire substrates reach a value as small as 0.25° and 0.18°, respectively. The relationship between the intensities of the peaks at 438 and 579 cm−1 in ZnO Raman spectra and deposition temperature were also investigated. Average roughness and surface morphology of the ZnO thin films deposited on Si substrates were evaluated by AFM.

Optical and surface properties of ZnO thin films by PLD

ZnO films have been grown on silicon (100) and sapphire (0001) substrates by pulsed laser deposition (PLD). The influences of substrate temperature and laser fluence on the properties of the films were studied. The effects of annealing on the ZnO films were investigated by X-ray photoelectron spectroscopy (XPS). The surface properties of ZnO were studied by scanning tunneling spectroscopy (STS). The band edge emission properties of the ZnO films have been studied by the photoluminescence spectroscopy (PL).

Pulsed laser deposition of AlN thin films

Aluminium nitride thin films were deposited at room temperature on silicon substrates by nitrogen-ion-assisted pulsed laser ablation of a hexagonal AlN target. A KrF excimer laser with pulse duration of 23 ns and wavelength of 248 nm was used as a laser source for the ablation. With this technology, it is possible to independently control the energy of the AlN radicals in the ablated plasma and the nitrogen ions in the ion beam to improve the quality of the deposited thin films. Moreover, the nitrogen ion implantation can also compensate the loss of nitrogen species in the ablation process. X-ray diffraction (XRD), Raman spectrum and x-ray photoelectron spectroscopy (XPS) were used to characterize the deposited thin films. The deposited thin films exhibit good crystal properties with sharp XRD peaks. The influences of the nitrogen ion beam energy on the electronic and structural properties of the deposited thin films were studied. The nitrogen ions can effectively promote the formation of stable Al-N bonds and improve the crystal properties of the deposited thin films. A nitrogen ion energy of 400 eV is proposed.

Surface and optical properties of nanocrystalline GaN thin films on sapphire (0001) by pulsed laser deposition

GaN thin films have been grown on sapphire substrates by pulsed laser deposition. The thin films deposited at different substrate temperature have been evaluated by x-ray diffraction (XRD), photoluminescence spectroscopy (PL), and x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM). The influences of depositing temperature on surface and optical properties of the GaN thin films have been studied. The XRD result show that the lowest full width at half maximum of x-ray diffraction line of the GaN film was deposited at about 700 degrees C. The photoluminescence (PL) spectra were measured at 7 K. The quantum confinement effects of the nanocrystalline GaN films have been evaluated by the band edge PL peaks. The energy shift of the band edge PL peaks of GaN film deposited at 700 degrees C have been estimated by the effective mass approximation method. The chemical composition and the native oxide of the GaN film surface were investigated by the XPS spectra. Average roughness and surface morphology of the GaN thin films deposited on the sapphire substrates have been evaluated by AFM.

Carbon nitride thin films deposited by nitrogen-ion-assisted laser ablation of graphite

Carbon nitride thin films were deposited on silicon wafers by pulsed KrF Excimer (wavelength 248 nm, duration 23 ns) ablation of graphite. Different excimer fluences and pressures of the nitrogen atmosphere were used in order to achieve a high nitrogen content in the deposited thin films. In another case, a Kaufmann-type ion source was used to produce a nitrogen ion beam to assist the deposition process. X-ray photoelectron spectroscopes (XPS) were used to identify the binding structure and the content of the nitrogen species in the deposited thin films. The thin films deposited in nitrogen atmosphere had N/C ratio of 0.42, whilst those deposited with assistance of nitrogen ion beam bombardment had N/C equals 0.43. The dependence of the optical parameters of the deposited films, the refractive n and extinction coefficient k, were studied by Ellipsometry.

Deposition of boron-carbon-nitrogen ternary thin films by ion-beam-assisted excimer ablation of B4C target

Boron-Carbon-Nitrogen thin films were deposited by laser ablation of B4C target under nitrogen ion-beam bombardment. The deposited thin films were set for X-ray photoelectron spectroscopy (XPS) and ellipsometry measurements. The results showed that in the ternary thin films, boron, carbon and nitrogen species were chemically bound to each other instead of simle mixtures. The B-C bonds were broken by the introduced energetic nitrogen ions and, subsequently, C-N and B-N bonds can be formed. The ellipsometry measurement gave the optical band gap of 0.48 eV for the thin films deposited under 50 eV nitrogen ion beam bombardment. According to the analyses, the nitrogen ion beam energy should be lower than 100 eV in most cases.