Jiahua Min

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.

Carrier transport performance of Cd0.9Zn0.1Te detector by direct current photoconductive technology

In this paper, based on the derivation of the Hecht model and Many model, we establish a new theoretical model and deduce its mathematical equation by considering an even-distributed charged center of certain concentration under constant illumination. This model helps us deeply understand the carrier transport performance of Cd0.9Zn0.1Te (CZT) under various illuminations and non-uniform distribution of the internal electric field in CZT. In our research, direct current photoconductive technology (DCPT) is applied to assess the electrical transport properties of carriers in CZT crystals, which is verified by room temperature Am-241 alpha-particle responses and charge collection efficiency test. The mobility-lifetime product ( μτ) for carriers is extracted from fitting the Hecht model by DCPT for CZT radiated from the cathode and anode by a constant laser, respectively. Moreover, the carrier transport properties of CZT under various light intensities and during a wide range of temperatures are also taken an...

A CMOS charge sensitive preamplifier for CdZnTe detector

In this work, a low noise and low power charge sensitive preamplifier (CSA) based on CSMC 0.6 µm double poly mix CMOS technology was designed and simulated. In this design, two MOSFETs were used as a feedback resistor and a feedback capacitor respectively to replace an on-chip resistor in parallel and an on-chip capacitor in a conventional CSA. Simulation results show that this design can reduce the noise level of the CSA and the area of the layout. The noise of the CSA can be less than several electrons, which can be calculated from the simulation results, and the power consumption is about 2.2mW/channel. Four channels can be placed in a 0.6×0.6 mm2 chip.

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.

Study on Cd vacancy in CdZnTe Crystal by Positron Annihilation Technology

Cd vacancies in cadmium zinc telluride(CdZnTe) crystals have an important effect on the crystal properties. In this paper, position distribution and concentration change of Cd vacancy in CdZnTe crystal grown by the temperature gradient solution growth (TGSG) were investigated by positron annihilation technology (PAT), which was based on the potential energy distribution and probability density of the positron in the crystal. The results showed that, the density of Cd vacancy increased obviously from the first-to-freeze to stable growth of the ingots, while decreased along the radial direction of the ingots.

The research on the surface structure and conductivity of free-standing diamond films for photo-transistor applications

Free-standing polycrystalline diamond films with a thickness of about 200 μm were grown by microwave plasma chemical vapor deposition (MPCVD) method. Raman spectra indicated high quality diamond film of the nucleation surface. AFM result indicated the nucleation surface was quite smooth with a mean surface roughness (RMS) of about 10 nm. The sheet carrier densities and sheet resistivities of hydrogenated nucleation surfaces of diamond film under different annealing temperatures were investigated by Hall effect measurement. The sheet carrier density and sheet resistivity remained in a relatively stable range until the annealing temperature above 200 ºC, and the sheet carrier density dropped drastically and sheet resistivity rose sharply, achieving a sharp change at an annealing temperature of 250 °C. The ultra-violet Raman spectra and infrared spectra showed CHx stretching modes at the hydrogenated nucleation surface, whereas almost little hydrogen incorporation on annealed sample.

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.

Study of Te Inclusion and Related Point Defects in THM-Growth CdMnTe Crystal

This study establishes a model for describing the interaction between Te inclusions, dislocations and point defects in CdMnTe crystals. The role of the complex environment surrounding the formation of Te inclusions was analyzed. Images of Te inclusions captured by scanning electron microscope and infrared microscope were used to observe the morphology of Te inclusions. The morphology of Te inclusions is discussed in light of crystallography, from the crystal growth temperature at 900°C to the melting temperature of Te inclusions using the traveling heater method. The dislocation nets around Te inclusions were calculated by counting lattice mismatches between the Te inclusions and the bulk CdMnTe at 470°C. The point defects of Te antisites were found to be gathered around Te inclusions, with dislocation climb during the cooling phase of crystal growth from 470°C to room temperature. The Te inclusions, dislocation nets and surrounding point defects are considered to be an entirety for evaluating the effect of Te inclusions on CdMnTe detector performance, and an effective mobility-lifetime product (μτ) was obtained.