Yongbiao Qian

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.

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.

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.

Fabrication of Capacitive Frisch Grid CZT Detector

The weighting potential distribution on a capacitive Frisch grid CZT detector and fabrication processing of the device have been investigated in this paper. The simulation results show that a bigger ratio of L/H helps to compress the weighting potential and the primary experimental results show that FWHM of the energy spectra of 241 Am increases by 4% when the L/H of the device increases from 50% to 100% and the capacitive Frisch grid can largely improve the detector performance, compared with the conventional planar geometry radiation detectors

Investigation of Passivation Layer of CdZnTe Detector

The process of surface passivation of CdZnTe(CZT) plays dominant role in detector performance, which can decrease the noise of the detector and improve the spectral energy resolution. The thickness of the passivation film has been measured by infrared spectroscopic ellipsometry in this paper. The relationship between thickness of the passivation films and the passivation time was obtained. The results show that the thickness of three samples passivated for 5 min, 10 min, 15 min are 15.669 nm, 17.288 nm and 24.434 nm, respectively