Jianyong Teng

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

The research of package for CdZnTe detector based on the capacitive Frisch grid structure

In this paper, the design and fabrication of a capacitive Frisch grid structure for CdZnTe (CZT) detector were investigated. The aging tests were first used to investigate the degradation of the mechanical and electrical characteristics of the CdZnTe detector based on the capacitive frisch grid structure. The effects of the degradation on the performance of CdZnTe detectors were investigated by scanning acoustic microscopy (SAM) test, current-voltage test, and multichannel pulse-height spectrum analysis. In particular, a passivation layer obtained by a two-step passivation processing, combined with a Teflon tape, was used as an insulated layer of the capacitive Frisch grid detector, improving its stability effectively at high voltages. However, further improvements in material and device fabrication (including insulated layer) were required to realize the potential of CZT detectors with the capacitive Frisch grid structure.

Investigation on the two-step passivation process for CdZnTe detectors

In this paper, the composition, morphology and electrical properties of the passivation layer for CdZnTe detectors were investigated. A two-step passivation was performed under different conditions, including passivation time, temperature and NH4F/H2O2 concentration. The obtained passivation layers were characterized by XRD, SEM, XRF and I-V methods. The results showed that the best passivation condition was with the NH4F/H2O2 concentration of 10wt%, passivation time of 40min and temperature of 20ºC. Under this condition, the passivation layer was purely oxidized and compact, and the surface leakage current of CZT crystals was most effectively reduced.

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