Wenbin Sang

The grain boundary related p-type conductivity in ZnO films prepared by ultrasonic spray pyrolysis

Intrinsic p-type ZnO thin film was fabricated on sapphire substrate by ultrasonic spray pyrolysis, the p-type ZnO film is achieved using O2 as the carrier gas, with a resistivity of 2.18 Ω cm−1, a carrier concentration of 1.10×1016 cm−3, and a high Hall mobility of 261 cm2/V s. The scanning capacitance microscopy images and annealing the p-type ZnO indicate that the absorbed oxygen in the grain boundary (GB) aroused the p-type conductivity, and the high Hall mobility of the p-type ZnO film own to the quasi-two-dimensional hole gas, which was induced by the negatively charged interface states in the GBs.

Electrical properties of contacts on P-type Cd0.8Zn0.2Te crystal surfaces

Abstract In this paper effects of surface treatments of p-type Cd0.8Zn0.2Te devices were studied by Atomic Force Microscopy (AFM), I–V measurements, and electrical properties as well as different contact technologies using Au, Al, In and electroless Au. It is shown that electroless Au film deposited by the chemical method can form a heavily doped p+ layer on a smooth surface, which is nearly ohmic on p-type material. Electroless Au gives better contact than evaporated Au, Al or In. A post-annealing treatment of electroless Au film improves the ohmic quality of contacts and enhances the adhesion between contact layer and the Cd0.8Zn0.2Te crystal surface.

Kinetics of the Coordination Transformation for Preparation of Nanosized ZnS in a PVA Film

Abstract This study was focused on the pervasion process of sulfion in a PVA–Zn2+ complex film. A diffusion equation for this process, based on the Fick first diffusion law, is suggested, which was in good agreement with the experimental results. The diffusion constant was 9.92 × 10−6 cm2/sec, calculated by combining the model and the experimental results.

Readout and signal processing electronics for 2×2 CZT detectors in parallel

In this paper, the readout system for 2×2 CdZnTe (CZT) detectors in parallel was designed and fabricated with analog electronics. The equivalent noise with this readout system was in the range of 223 electrons RMS for Cd=0 pF to 1785 electrons RMS for Cd=330 pF. The output signal of the preamplifier was about 130 mV, the signal duration was about 0.2 ms and the signal rise time was about 900 ns, when the CZT detector biased at -1250 V was exposed to the radiation source 137Cs (662 keV)with the shaping time of 2.2 us. The ratio of signal to noise (SNR) is about 27:1, after the signal through summing circuit.

Investigation of annealing on Au/p-CdZnTe Contact

The effects of annealing for different periods at 373K in air on the properties of the contact between Au and p-CdZnTe have been investigated by current-voltage (I-V), shear-off-test and scanning acoustic microscopy (SAM) in this paper. It is found that annealing at 373K in air for 2h can get lower Schottky barrier height, better ohmic contact property and can enhance the adhesion force by 27%, but the continuity of the contact interface is deteriorated, compared with that before annealing. However, annealing at 373K in air for 4h will greatly increase the leakage current, the reason for which might be that the stoichiometric proportion of CdZnTe crystal has been changed

Synthesis and Optical Properties of CdS Nanocrystals in Polyacrylonitrile Film

A novel process using polyacrylonitrile (PAN) containing well-distributed ligands as a medium for forming CdS nanocrystals by an ion coordination method is presented in this paper. PAN consists of a large number of repeat units, and each unit has a ligand or group like CN and CO. A metal ion with a strong capability of complexing, such as Cd, Zn, Mn, etc., can complex with the group in PAN, and the complexed metal ion will react with negative ionlike S2− to be transformed into semiconductor nanocrystals. This growth mechanism has been identified by the results of Infrared Spectroscopic Analysis. The typical morphologies observed by TEM show that the CdS nanocrystals are rather evenly distributed throughout the PAN film and the size is estimated to be about 1–10 nm in diameter, depending on the growth parameters. The results of x-ray diffraction show that the crystallites of CdS nanocrystals in PAN film might be a mixture of crystals including both α-hexagonal CdS and β-cubic CdS. Quantum-size effects at room temperature have been demonstrated using ultraviolet–visible absorption spectra, excitation, and emission spectra, respectively. A rather sharp and strong emission band peaked at about 610 nm was observed and its mechanism is also briefly discussed.

Dielectric Properties in Ferroelectric Optically Active Polyamides

A relationship between dielectric constant ε or dielectric loss tan δ and structure was studied for optically active polyamides. The samples of these polyamides exhibited a chiral smectic phase due to their asymmetric structures and strong hydrogen bonds. The dielectric parameters were significantly influenced by temperature, but were hardly affected by frequency in the high-frequency region. The hindered rotations of the mesogens, which affect the polarization, depended on the structures and the phase transitions.

Study on CdZnTe crystal growth parameters optimization

The factors influencing the shape of solid-liquid interface during the process of CdZnTe vertical Bridgman growth were investigated in this paper. The relationship between the temperature gradient and the solid-liquid interface parameter ¿ near the growth interface with different crucible dropping rate was obtained. Here ¿ represents the solid-liquid interfacial concave-convex extent. If ¿ is positive, the solid-liquid interface will be convex into solid phase region and if ¿ is negative, the solid-liquid interface will be convex into liquid phase region. Simulation results show that when the crucible dropping rate (Vp) was rather high (Vp = 50 mm/h), the value of ¿ dropped greatly with the increase of the solid-liquid interface temperature gradient, and when Vp was low (for example, Vp = 0.1 mm/h), the value of ¿ declined slowly and had a trend of turning positive value to negative value with the increase of temperature gradient. In particular, when Vp was about 1 mm/h, the solid-liquid interface tended to be flat with the increase of the temperature gradient. Therefore, it might be concluded that when the temperature gradient of solid-liquid interface was greater than 10 K/cm, and Vp was about 1 mm/h, rather flat solid-liquid interface during the process of crystal growth could be obtained. In addition, based on the simulation results, actual crystal growth experiments were implemented. The experimental results are roughly consistent with the simulation results.

Oxidized layer of CdZnTe studied by C-V characteristics

In this paper, the CZT oxidized layers on cadmium zinc telluride (CZT) wafer formed by two-step chemical passivation process (KOH-KCl + NH4F/H2O2) were investigated by using XRD, ED-XRF, SEM. The results show that the oxidized layer obtained by using this process has a very uniform and compact morphology and consists mainly of TeO2, TeO3 and CdTeO3. In particular, the thickness of the oxidized layer on the CZT was obtained by using C-V measurements for the first time. The dependence of the thickness of the oxidized layer on the passivation time was obtained and the main factors influencing the results of the C-V measurements were also discussed.

The study of ZnO thin film fabricated by low temperature wet chemical method and its optical properties

The optical properties of the nano-ZnO thin films were studied, which were prepared by low temperature wet chemical-method combined with ultrasonic treatment. The thin film could emit the strong UV and blue light. The blue emission was caught by the interstitial zinc (Zni), which could be confirmed by Raman spectrum. The relationship of the optical properties and processing parameters was also discussed. The reaction temperature, the reaction time and the different molar ratios of Zn2+ to TEA could affect on the intensities of the UV emission and the blue emission of the ZnO thin film, respectively. The mechanism of the phenomena was brought forward by analyzing the FTIR spectrum.