Yongbiao Bai

Corrosion behavior of biomedical Ti-24Nb-4Zr-8Sn alloy in different simulated body solutions

Corrosion behavior of a multifunctional biomedical titanium alloy Ti-24Nb-4Zr-8Sn (wt.%) in 0.9% NaCl, Hanks solution and artificial saliva at 37 °C was investigated using open circuit potential, impedance spectroscopy and potentiodynamic polarization techniques, and some results were compared with pure titanium and Ti-6Al-4V alloy. The results showed that the alloy exhibited good corrosion resistance due to the formation of a protective passive film consisting mainly of TiO2 and Nb2O5, and a little of ZrO2 and SnO2. Ca ions were detected in the passive film as the alloy immersed in Hanks and artificial saliva solutions and they have negative effect on corrosion resistance. The EIS results indicated that either a duplex film with an inner barrier layer and an outer porous layer or a single passive layer was formed on the surface, and they all transformed into stable bilayer structure as the immersion time increased up to 24h. The polarization curves demonstrated that the alloy had a wider passive region than pure titanium and Ti-6Al-4V alloy and its corrosion current density (less than 0.1 μA/cm(2)) is comparable to that of pure titanium.

Effect of Annealing on the Characteristics of Pd/Au Contacts to p-Type GaN/Al0.45Ga0.55N

The effect of annealing on the characteristics of Pd/Au contacts to p-type GaN/Al0.45Ga0.55N was investigated. The electrical characteristics of Pd/Au contacts and a p-GaN/AlGaN sample were measured after annealing at different temperatures from 550°C to 850°C. Changes in the surface electrical characteristic of p-GaN/AlGaN material were observed after each annealing step. It is indicated that the surface electrical characteristic of p-GaN/AlGaN material plays an important role in the current transport through Pd/Au pads. A possible reason for those changes is impurity contamination, most likely oxygen and carbon contamination introduced from processing. The microstructure of Pd on p-GaN/AlGaN was investigated by glancing-incidence x-ray diffraction (GXRD). The results of GXRD show that the AlPd2 and GaPd2 phases were formed at the interface after annealing, and the formation of these phases could be effective for forming ohmic contacts on p-GaN/AlGaN.

Performance improvement of c-Si solar cell by a combination of SiNx/SiOx passivation and double P-diffusion gettering treatment

SiN x /SiO x passivation and double side P-diffusion gettering treatment have been used for the fabrication of c-Si solar cells. The solar cells fabricated have high open circuit voltage and short circuit current after the double P-diffusion treatment. In addition to better surface passivation effect, SiN x /SiO x layer has lower reflectivity in long wavelength range than conventional SiN x film. As a consequence, such solar cells exhibit higher conversion efficiency and better internal quantum efficiency, compared with conventional c-Si solar cells.

Carbon agent chemical vapor transport growth of Ga2O3 crystal

Beta-type gallium oxide (β-Ga2O3) is a new attractive material for optoelectronic devices. Different methods had been tried to grow high quality β-Ga2O3 crystals. In this work, crystal growth of Ga2O3 has been carried out by chemical vapor transport (CVT) method in a closed quartz tube using C as transport agent and sapphire wafer as seed. The CVT mass flux has been analyzed by theoretical calculations based on equilibrium thermodynamics and 1D diffusional mass transport. The crystal growth experimental results are in agreement with the theoretical predictions. Influence factors of Ga2O3 crystal growth, such as temperature distribution, amount of C as transport agent used, have also been discussed. Structural (XRD) and optical (Raman spectroscopy, photoluminescence spectrum) properties of the CVT-Ga2O3 crystal are presented.

Electrical and optical property of annealed Te-doped GaSb

GaSb is the most suitable substrate in the epitaxial growth of mixed semiconductors of GaSb system. In this work, Te-doped GaSb bulk crystals with different doping concentration have been annealed at 550 ℃ for 100 h in ambient antimony. The annealed samples have been studied by Hall effect measurement, infrared (IR) optical transmission, Glow discharge mass spectroscopy (GDMS) and photoluminescence (PL) spectroscopy. After annealing, Te-doped GaSb samples exhibit a decrease of carrier concentration and increase of mobility, along with an improvement of below gap IR transmission. Native acceptor related electrical compensation analysis suggests a formation of donor defect with deeper energy level. The mechanism of the variation of the defect and its influence on the material properties are discussed.

Thermally induced native defect transform in annealed GaSb

Undoped p-type GaSb single crystals were annealed at 550–600 °C for 100 h in ambient antimony. The annealed GaSb samples were investigated by Hall effect measurement, glow discharge mass spectroscopy (GDMS), infrared (IR) optical transmission and photoluminescence (PL) spectroscopy. Compared with the as-grown GaSb single crystal, the annealed GaSb samples have lower hole concentrations and weak native acceptor related PL peaks, indicating the reduction of the concentration of gallium antisite related native acceptor defects. Consequently, the below gap infrared transmission of the GaSb samples is enhanced after the thermal treatment. The mechanism about the reduction of the native defect concentration and its influence on the material property were discussed.