Evaluation of CdZnTeSe as a high-quality gamma-ray spectroscopic material with better compositional homogeneity and reduced defects

Abstract

X- and gamma-ray detectors have broad applications ranging from medical imaging to security, non-proliferation, high-energy physics and astrophysics. Detectors with high energy resolution, e.g. less than 1.5% resolution at 662 keV at room temperature, are critically important in most uses. The efficacy of adding selenium to the cadmium zinc telluride (CdZnTe) matrix for radiation detector applications has been studied. In this paper, the growth of a new quaternary compound Cd_0.9Zn_0.1Te_0.98Se_0.02 by the Traveling Heater Method (THM) is reported. The crystals possess a very high compositional homogeneity with less extended defects, such as secondary phases and sub-grain boundary networks. Virtual Frisch-grid detectors fabricated from as-grown ingots revealed ~0.87-1.5% energy resolution for 662-keV gamma rays. The superior material quality with a very low density of defects and very high compositional homogeneity heightens the likelihood that Cd_0.9Zn_0.1Te_0.98Se_0.02 will be the next generation room-temperature detector material.

Figure 1

(a) As-grown Cd_0.9Zn_0.1Te_0.98Se_0.02 ingot with 52-mm diameter, grown by the THM, (b) Variation of Zn and Se (atomic %) along the length of the ingot, (c) Calculated band-gap along the length of the ingot. The inset shows the wafer cut along the length of the as-grown Cd_0.9Zn_0.1Te_0.98Se_0.02 ingot, and the map of PL peak energy positions at 7 K for the as-grown Cd_0.9Zn_0.1Te_0.98Se_0.02 wafer cut perpendicular to the growth axis, (d) (A°, X) peak mapping and (e) (D°, X) peak mapping. The mapping area is ~2.8 × 3.0 cm².

Figure 2

X-ray topographic image of an as-grown Cd_0.9Zn_0.1Te_0.98Se_0.02 sample. Exposed area: ~5.5 × 5.5 mm².

Figure 3

(a) Plot of the charge collection versus applied bias for the as-grown CZTS planar detector at room temperature. The 59.6-keV line was used from an ²⁴¹Am source. The solid line indicates the Hecht fitting to extract the µτ value for electrons, the inset in Fig. 1a shows the IR transmission image of the whole sample of dimensions ~6.65 × 5.7 × 1.86 mm³, (b–d) high magnification IR transmission microscopic images of an as-grown CZTS sample showing triangular Te inclusions.

Figure 4

Current-voltage characteristics and gamma response for the Frisch grid detector fabricated from an as-grown CZTS ingot at room temperature. (a) Dark I–V characteristics of the detector sample at room temperature, (b) Detector response (energy resolution at 662 keV) at different shaping times, (c) Pulse height spectrum for the Frisch grid detector from a ¹³⁷Cs source, the inset shows the photograph of the detector, (d) Pulse height spectrum for the Frisch grid detector for a ²²Na source, (e) Zoomed version of the same spectrum to enhance the high energy peak, (f) Pulse height spectrum for the Frisch grid detector for a ¹³³Ba source, (g) Zoomed version of the same spectrum to enhance the high energy peaks, and (h) Pulse height spectrum for the Frisch grid detector for a ⁶⁰Co source showing very well resolved high energy gamma lines at energies of ~1.17 MeV and 1.33 MeV. The detector dimensions are: ~4.5 × 4.5 × 10.8 mm³.