Na Fu Wang

A novel cross-shape DGS applied to design ultra-wide stopband low-pass filters

This letter presents a novel low-pass filter with an ultra-wide stopband. The proposed filter is comprised of a new cross-shape defected ground structure (CSDGS). By using this structure, the filter not only supports conventional DGS performances with a sharp rejection, but also exhibits an ultra-wide stopband. For the deigned low-pass filter, an insertion loss of less than 2dB from dc to 3.5GHz and the rejection is better than 20dB from 4.3 to 15.8GHz. Predicted performances show widened and deepened stopband beyond the low passband. Furthermore, it is confirmed by measurement.

IMPROVED FORMATION OF SILICON DIOXIDE FILMS IN LIQUID PHASE DEPOSITION

This work is to reveal the novel technique of liquid phase deposition silicon dioxide (SiO2) films which will increase the deposition rate and also improve the film quality. It is well known that deposition at a lower temperature without residual OH− on the substrate is difficult to achieve. Therefore, it is important to treat the substrate wafer before deposition. The substrate surface dipped into hydrofluoric acid (HF) is usually terminated with hydrogen (H) and has hydrides (Si–H) which react with water so that hydroxyls (Si–OH) can be obtained. No silicon dioxide can be grown on a clean Si substrate without native oxide. Therefore, a model is proposed to show that native oxide growth with chemical pretreatment of HF and ultrapure deionized water has rich hydroxyl (OH) molecules on surface in order to grow silicon dioxide. Another constant parameter, the growth rate of SiO2 is found to increase linearly with the time of reaction with ultrapure deionized water. At the same concentration of boric acid an...

Extremely low temperature formation of silicon dioxide on gallium arsenide

This article demonstrates the growth of silicon dioxide (SiO2) on a gallium arsenide (GaAs) substrate by use of the liquid phase deposition (LPD) method at extremely low temperature (∼40 °C). This method cannot only grow SiO2 but it can also obtain good quality and reliability due to the suppression of interdiffusion in such a low temperature process. The deposition rate of LPD-SiO2 on GaAs is up to 1265 A/h. The refractive index of the LPD-SiO2 film on GaAs is about 1.42 with growth at 40 °C. When the LPD-SiO2 film on the GaAs substrate is used to fabricate a metal–oxide–semiconductor capacitor with a device area of 0.3 cm2, the surface charge density (Qss/q) is about 3.7×1011 cm−2 and the leakage current is 43.3 pA at −5 V. A proposed mechanism for the LPD of SiO2 on GaAs is also presented.

Porous SiO 2 /MgF 2 broadband antireflection coatings for superstrate-type silicon-based tandem cells

The purpose of this study is to reduce the glass substrate reflectivity over a wide spectral range (400-1200 nm) without having high reflectivity in the near-infrared region. After making porous SiO₂/MgF₂ double-layer antireflection (DLAR) thin film structure, the superstrate-type silicon-based tandem cells are added. In comparison to having only silicon-based tandem solar cells, the short-circuit current density has improved by 6.82% when porous SiO₂/MgF₂ DLAR thin film is applied to silicon-based tandem solar cells. This study has demonstrated that porous SiO₂/MgF₂ DLAR thin film structure provides antireflection properties over a broad spectral range (400-1200 nm) without having high reflectivity at near-infrared wavelengths.

Bond Structure in Porous SiOCH Low-k Film Fabricated by Ultraviolet Irradiation

Using an advanced ultraviolet irradiation (UV curing) process, a high performance porous low-k film of k=2.57, whose Youngs modulus is larger than 8 GPa, now is developed to improve the mechanical properties of a film by the reconstruction of Si–O network structure from cage-like Si–O bonds, suboxide structures and Si–CH3 bonds. It was found that the UV curing process can efficiently strengthen the mechanical properties of porous low-k film, and reduce its dielectric constant value by removing hydrocarbon bonds to form porosities. As a result, the key features of this optimal SiOCH material, high elastic modulus and a low dielectric constant, provide promising properties for future integrated schemes.

Near Room-Temperature Growth of SiO2 Films for p-HgCdTe Passivation by Liquid Phase Deposition

We first propose a low temperature process (35° C–45° C) for the growth of high-quality SiO2 layer on p-HgCdTe by liquid phase deposition (LPD). In this new formation technology, the surface of HgCdTe substrates was treated with suitable ammonia solution to enhance the generation of OH- radicals which is favorable to the formation of SiO2 films. The refractive index of the SiO2 films is close to 1.465 under the typical growth conditions. The leakage current, surface charges density, and dielectric breakdown strength of the test samples, measured at 77 K, are found to be 0.356 nA (at -5 V), -7.04×1010/ cm2, and 650 kV/cm, respectively which are comparable to other techniques. The film quality demonstrates its potential in fabricating infrared devices.

DEPOSITION OF HIGH QUALITY SILICON DIOXIDE ON HG1-XCDXTE BY LOW-TEMPERATURE LIQUID PHASE DEPOSITION METHOD

A low temperature (35–45 °C) process of liquid phase deposition (LPD) for the growth of silicon dioxide (SiO2) on Hg1−xCdxTe is proposed. To enhance the formation of SiO2, the HgCdTe surface has to be treated by ammonia solution before LPD. A thin native oxide which is formed by previous surface treatment involving OH− radicals greatly enhances the SiO2 deposition on HgCdTe. Thus, SiO2 films with a high refractive index (1.465) and a low p-etching rate (34 A/s) were obtained. Auger electron spectroscopy depth profile shows less interdiffusion of constituent atoms between the SiO2 layer and the HgCdTe substrate. Electrical properties of the SiO2/p-HgCdTe interface are also characterized at 77 K. It is found that the p-HgCdTe surface is accumulated and the effective surface charge density is estimated to be −2.25×1010 cm−2. The leakage current and dielectric breakdown strength are also found to be 0.356 nA (at −5 V) and above 650 KV/cm, respectively. Furthermore, the growth mechanism of LPD-SiO2 on HgCdTe i...

CO2 Laser Annealing on Fluorinated Silicon Oxide Films

CO2 laser annealing of fluorinated silicon oxide films grown by liquid-phase deposition (LPD) is proposed to improve the properties of the as-deposited films. It is found that the fluorinated silicon oxide films after laser annealing become much denser and that the effective surface charge density (QSS/q) is reduced significantly. However, the properties of the fluorinated silicon oxide films after laser annealing depended on the power density of the laser beam. It is also found that the effect of laser annealing is most prominent when the power density of the laser beam is controlled at 12 KW/cm2. Based on the experimental results, it may be expected that the structure of a fluorinated LPD-SiO2 film following CO2 laser annealing is similar to those of the thermally grown layers. Thus, CO2 laser annealing is the best candidate for improving the properties of LPD oxide films.

Effect of fluorine concentration on the metal-insulator-semiconductor (MIS) solar cell output performance by liquid phase deposition

Metal-insulator-semiconductor (MIS) solar cells with the insulating layer fabricated by liquid phase deposition (LPD) method has been shown to have good output performance in various literature published. In this paper, a high quality insulating layer is developed via LPD method with the fluorine content controlled by the growth solution concentration. The addition of fluorine to enhance the solar cell efficiency is first discussed. Then an optimum fluorine content is suggested at the end of this paper. The value of the fluorine content is controlled by growth solution concentration. Solar cells with thin fluorinated oxide film reveals good performance in the illuminated characteristics. And thus novel fluorinated thin oxide film is a good candidate for the replacement of existing MIS junction I-layer.

Effects of substrate preheating for the growth of ZnxCd1 - XTe/(1 0 0)GaAs by MOCVD

A process for the growth of ZnCdTe(100)GaAs heteroepitaxial films using metalorganic chemical vapor deposition (MOCVD) has been developed. It is found that substrate baking pretreatment deeply affects the characteristics of ZnxCd1 − xTe(x < 0.09) on (100)GaAs substrate (such as ZnCdTe film orientations, the Zn composition in the ZnCdTe compound alloys and the quality of ZnCdTe epilayer). We compared measurements on the same set of samples by photoreflectance (PR) and photoluminescence (PL). It was found that baking temperature (or baking time) may affect the relative contribution of each transition, resulting in a shift of the transition energy. We speculate that (100)GaAs substrates may undergo decomposition at a high baking temperature, leading to the GaAs surface change from As-stabilized surface to Ga-stabilized surface, resulting in better film PL quality and different film orientation. At higher baking temperature (or baking time), the ZnCdTe epilayer tends towards a (1 1 1) orientation and the film quality is obviously improved. Up to a temperature of around 640°C, the quality begins to decline sharply due to the destruction surface.