Yinyue Wang

Structural and optical properties of ZnO films grown on the AAO templates

Abstract Structural and optical properties of ZnO films grown on Al substrate and anodic alumina oxide (AAO) templates by rf magnetron reactive sputtering deposition were investigated using X-ray diffraction (XRD), atomic-force microscope (AFM) and photoluminescence (PL). We found that ZnO thin films on Al substrate show good C-axis orientation, while the orientation of ZnO film on AAO templates is disordered, this due to the fact that the crystalline of ZnO is greatly influenced by surface morphology of substrates. PL measurements show a blue band in the wavelength range of 400–500 nm caused by the interstitial Zn in the ZnO films. The intensity of emission peak of ZnO films deposited on AAO templates increases compared with that on the Al substrate. Combining electrical resistivity and carrier concentration measurements, we found that that the blue emission intensity is consistent with the concentration for the interstitial zinc in the ZnO films.

Raman scattering and room-temperature visible photoluminescence from Ge nanocrystals embedded in SiO2 thin films

Germanium nanocrystals (nc-Ge) embedded in SiO2 glassy matrix have been prepared on glass substrates and silicon (100) wafers by an rf cosputtering technique and post-annealing treatment in vacuum atmosphere. Using Raman spectrometry, X-ray diffraction, and UV/VIS/NIR transmittance and reflectance measurements, we have investigated the structures and the optical properties of the Ge-SiO2 composite films. The results show that Ge nanocrystals could be formed in Ge-SiO2 composite films by thermal annealing. The growth of nc-Ge is associated with the thermodynamical breakup of GeO bonds and/or evacuation of oxygen atoms. As the size of nc-Ge reaches 4.6 nm, the efficient optical band gap of the Ge-SiO2 composite film is found to shift to higher energy. Furthermore, broad-band multi-peak photoluminescence (PL) spectra are observed at room temperature. It is found that there exist Ge nanocrystals only in the emitting samples, and the emitting energy is approximately 2.05 eV. The multi-peak PL spectrum is considered to result from the different local environments of Ge nanocrystals in annealed sample.

Ohmic contacts to boron-doped diamond

Abstract Two types of contacts, namely Au and Au/Ta, were fabricated on B-doped diamond films by rf sputtering deposition. I–V measurements show that our Au and Au/Ta contacts have exhibited good ohmic characteristics in their as-deposited states. Upon annealing, their ohmic behaviors were improved to different extent. Compared with Au contact, Au/Ta contact has lower specific contact resistance value and better adhesion. X-ray photoelectron spectroscopy (XPS) analyses indicate that there is an obvious interdiffusion between Au and diamond film in Au contact. The interdiffusion was enhanced by annealing. This interdiffusion layer may be the reason why Au contacts are ohmic in the as-deposited and annealed states. As for Au/Ta contacts, XPS analyses show the formation of TaC at the interface between Ta and diamond film in the as-deposited state, there is an increase of TaC in the annealed contact. The presence of TaC promotes our Au/Ta contacts to have better ohmic characteristic.

OHMIC CONTACTS ON DIAMOND BY R. F. SPUTTERING AND Ti-Au METALLIZATION

Low resistance ohmic contacts were fabricated on diamond films. A high boron concentration (~1020cm-3) was obtained on the surface by ion implantation. The initial film of Ti (20nm) followed by Au (100nm) was deposited by r. f. sputtering. I-V measurements showed that the as-deposited contacts were ohmic. Upon annealing, the ohmic characteristics of the contacts were improved significantly. The specific contacts resistivity decreased from 6.2 × 10-3 to 1.2 × 10-6Ωcm2 as a result of post-deposition annealing. The X-ray photoelectron spectroscopy analysis indicated the formation of titanium carbide at the Ti/diamond interface in the as-deposited and annealed states. A low oxygen concentration was observed.

Ohmic contacts on diamond by B ion implantation and Ta-Au metallization

Ohmic contacts on diamond have been achieved by B ion implantation and subsequent metallization with a Ta/Au bilayer. The pre-treatment of p-diamond film using boiling aqua regia was effective in reducing oxygen, which plays an important role in forming the Au/Ta/p-diamond ohmic contacts. Sputter deposition and implantation accelerate the interfacial reaction between Ta and diamond film. The formation of TaC makes our contacts to be ohmic in the as-deposited state. Upon annealing, the quantity of TaC increases and it makes the ohmic behavior be improved.

Ohmic contacts and interface properties of Au/Ti/p-diamond prepared by r.f. sputtering

The Au/Ti/p-diamond contacts were prepared by r.f. sputtering and I-V measurements showed that the as-deposited contacts were ohmic, Upon annealing at 500 degrees C for 10 min in a vacuum of 10(-4) Pa, the ohmic characteristics of the contacts were improved by 30%. The specific contact resistivity, which was calculated by the transmission line model (TLM), decreased from 2.9 x 10(-3) to 2.0 x 10(-3) Omega.cm(2) as a result of post-deposition annealing, Analysis by XPS indicated the formation of titanium carbide at the Ti/diamond interface in the as-deposited and annealed states. This gave the contacts their good ohmic characteristics. Copyright (C) 2000 John Whey & Sons, Ltd.

A study on photoluminescence from Si-rich silicon oxide films and Ge-containing silicon oxide films

Abstract Si-rich silicon oxide films and Ge-containing silicon oxide films were deposited using the RF magnetron sputtering technique with a Si–SiO 2 and a Ge–SiO 2 composite target, respectively. The percentage area ratio of Si to SiO 2 was 30%, and that of Ge to SiO 2 was 10%. These films were annealed in a N 2 ambient at 300°C, 600°C, 900°C, 1000°C or 1100°C for 30 min. All the PL spectra from the two types of films annealed at various temperatures have similar shapes with peak positions around 580nm (~2.1 eV). Annealing at 900°C or 1100°C, crystalline nanometer silicon particles (NSPs) in the Si-rich silicon oxide films and annealing at 900°C crystalline nanometer Ge particles (NGPs) in Ge-containing silicon oxide films can be observed using a high-resolution transmission electron microscope (HRTEM). The PL peak positions for Si-rich silicon oxide films do not show any correlation with the sizes of crystalline NSPs, and PL intensity does not show any correlation with the density of crystalline NSPs. The PL peak positions of both types of films do not show any shift when measurement temperature increases from 10 to 300 K. The PL mechanisms for the Si-rich silicon oxide films and Ge-containing silicon oxide films have been discussed.

Characterization of an ultra-low k SiO2 thin film prepared by molecular template

Using the molecular template method, we synthesized a nanoporous SiO2 thin film with ultra-low dielectric constant (k). Fourier transform infrared spectroscopy and differential thermal analysis were carried out to investigate the effect of n-hexane washing on the film properties before and after the surface modification process. The results showed the important role of the washing process, and revealed that –CH3bonds substituted for –OH bonds in the films modified by trimethylchlorosilane (TMCS)/n-hexane solution, which avoided the destruction of the network structure of the thin films. The nanometre pore size (10–20 nm), good network structure and thickness of SiO2 films were observed by scanning electron microscopy (SEM). The effects of the post-treatment conditions on the dielectric constant (1.5) and the porosity (78%) of the films were also investigated.

Formation of 6H–SiC due to subsequent annealing of sputtering a-SiC:H films

Abstract In this paper, the phase formation of 6H–SiC is studied through a 60 min isochronal annealing of a-SiC:H prepared at the substrate temperature of about 100°C by reactive rf sputtering. Infrared transmission, Raman scattering and X-ray diffraction analyses are employed to characterize the films before and after annealing. It shows that a-SiC:H deposited at higher rf power changes into 6H–SiC phase, along with the disappearance of silicon or carbon clusters existed in as-prepared films, at annealing temperature of 800°C, while 1000°C is required for the phase change of those deposited at lower rf power. It is suggested that the bombardment of energetic argon ions during deposition is responsible for the enhancement of 6H–SiC formation, decrease of hydrogen content, and homogeneity of the films.

Raman scattering and room‐temperature visible photoluminescence from Si nanocrystals embedded in SiO2 thin films

Silicon nanocrystals (nc-Si) embedded in SiO 2 glassy mixture have been prepared on glass substrates and silicon and germanium wafers by r.f. co-sputtering and post-annealing in a vacuum. Using Raman spectrometry, photoluminescence and electrical conductivity measurements, we have investigated the structures and the optical properties of the Si/SiO 2 composite films. The results show that Si nanocrystals could be formed in Si/SiO 2 composite films by thermal annealing. The growth of nc-Si is associated with annealing temperature and silicon content. As the size of nc-Si reaches 5 nm, the intensity of photoluminescence at room temperature is at a maximum and the emitting photon energy is 2.15 eV.