Study of CdZnTeSe Gamma-Ray Detector under Various Bias Voltages

Cadmium zinc telluride selenide (CdZnTeSe) is a new semiconductor material for gamma-ray detection and spectroscopy applications at room temperature. It has very high crystal quality compared to similar materials such as cadmium telluride and cadmium zinc telluride. The consistency of peak position in radiation detection devices is important to practical applications. In this paper, we have characterized a CdZnTeSe planar detector for bias voltages in the range of −20 V to −200 V and amplifier shaping time of 2, 3 and 6 μs. The peak position of the 59.6-keV gamma line of Am becomes more stable as the absolute value of the applied voltage increases. The best energy resolution of 8.5% was obtained for the 59.6-keV gamma peak at −160 V bias voltage and 3-μs shaping time. The energy resolution was relatively stable in the −120 V to −200 V range for a 6-μs shaping time. Future work will be focused on the study of the peak position and energy resolution over time.


Introduction
Cadmium zinc telluride selenide (CdZnTeSe or CZTS) has shown great promise DOI: 10.4236/msa.2020. 118036 554 Materials Sciences and Applications as a semiconductor material for fabricating cheaper gamma-ray detection and spectroscopy devices for applications at room temperature (i.e., without cryogenic cooling), compared to similar materials like cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe of CZT) [1] [2] [3] [4]. This advantage comes from the high crystal uniformity of CZTS compared to CdTe and CZT [2] [3]. A material with higher crystal uniformity and lesser defects will give more detector-grade wafers per volume of the as-grown ingot. Presently, CdTe and CZT have applications in gamma-ray spectroscopy, medical imaging, nuclear and radiological threat detection, and astrophysics. CZTS has the potential of reducing the cost of fabricating devices that could be used in these applications.
The stability of peak position and energy resolution in radiation detection devices are important for practical applications in radiation detection, spectroscopy, and imaging. Pérez et al. [5] studied the stability of CZT coplanar detectors over a period of four months. Shifts of about 0.5% in the photopeak positions were observed for the 662-keV gamma line of 137 Cs with the detectors maintained at a temperature of 22.5˚C ± 1.0˚C and electronic experimental parameters kept fixed [5]. Similar results were obtained for the 356-keV peak of 133 Ba and 1173-keV peak of 60 Co [5]. Degradation of energy resolution over time was observed, and fluctuations in the energy resolutions of the 356-keV peak of 133 Ba and 1173-keV peak of 60 Co were higher than that of the 137 Cs 662-keV peak [5].
It was concluded that increases in bias voltage and operating temperature led to a significant increase in noise, which had a greater effect on the low-energy peaks due to the smaller signal-to-noise ratio [5].
Egarievwe et al. [6] studied the detection and electrical properties of CZT at elevated temperatures, where the energy resolution of the 31-keV peak of 133 Ba was observed to be 16%, 18%, 28% and 38% at 24˚C, 30˚C, 40˚C and 50˚C respectively. The 31-keV peak position varied within 3 keV at 70˚C at an applied bias of 60 V. For bias voltages from 20 to 100 V, the fluctuation in the energy resolution was between 15% and 18% at 25˚C and between 22% and 38% at 50˚C. Studies involving cooling were carried out by Chun et al. [7] where an improvement of about 2% was recorded for the energy resolution from 30˚C to −40˚C for the 122-keV and 136-keV peaks of 57 Co. Maehlum et al. [8] studied 5 × 5 CZT detector modules under variations of temperature (20˚C -40˚C) and humidity (relative humidity 10% -70%), where they recorded an average photopeak variation of ±1 keV for the 122-keV peak of 57 Co over a period of 248 days.
In this paper, we present results on the study of the stability of the energy-peak position for a CdZnTeSe planar detector over an operating voltage range of −20 to −200 V. We also report on peak position changes based on the amplifier shaping time. by the traveler heater method [9]. The CZTS wafer was cut from the ingot using a diamond impregnated wire was. It was then polished using an 800-grit silicon carbide paper. This was followed by successively polishing with 100-grit and

Results
The current-voltage curve of the CZTS detector in the −200 to 200 V range is shown in Figure 1. The resistivity determined from the I-V curve is on the order of 10 10 Ω-cm.

Conclusion
CZTS has emerged as a very promising semiconductor material for producing cheaper gamma-ray and X-ray detectors for applications at room temperature without cryogenic cooling. The high crystal uniformity of CZTS and near ab-