Room-temperature semiconductor detectors, such as cadmium zinc telluride (CdZnTe), often are subjected to surface damage during fabrication, thus reducing their performance in detecting X-rays and gamma-rays. In this study, we compared two surface-passivation chemical solutions: Ammonium fluoride in hydrogen peroxide (NH ₄ F + H ₂ O ₂ + H ₂ O) and potassium hydroxide in hydrogen peroxide (0.1 g of KOH + 10 ml of 30% H ₂ O ₂ ). X-ray photoelectron spectroscopic analysis showed that the NH ₄ F-based solution is more effective at converting Te species on the CdZnTe surfaces into a more stable TeO ₂ layer, attaining values of 4.90 and 5.34 for the Te3d _3/2 O ₂ /Te3d _3/2 and Te3d _5/2 O ₂ /Te3d _5/2 peak-height ratios respectively, compared to the KOH-based solution with 1.25 and 1.19, respectively. The current-voltage measurements showed an increase in the bulk leakage current for freshly passivated samples compared to those of mechanically polished samples. However, within a period of about three to 14 days, their leakage currents reduced to values in the range of the mechanically polished samples. The resistivity of the CdZnTe samples is on the order of 1010 Ω-cm. The NH ₄ F-based chemical contributed less to the leakage current. Its leakage current at 60 V is 6.3 times that of the mechanically polished sample, compared to 30.5 for the sample passivated with the KOH-based solution. Analysis of the 59.5-keV peak of Am-241 showed that the sample passivated with the NH ₄ F-based solution has a better energy resolution compared to the one passivated with the KOH-based solution.

Cadmium zinc telluride selenide (Cd_1−xZn_xTe_1−ySe_y or CZTS) is one of the emerging CdTe-based semiconductor materials for detecting X- and gamma-ray radiation at or near room temperature (i.e., without cryogenic cooling). Potential applications of CZTS sensors include medical imaging, X-ray detection, and gamma-ray spectroscopy. Chemical passivation of CZTS is needed to reduce the conductivity of Te-rich surfaces, which reduces the noise and improves the device performance. In this study, we focus on the effect of surface passivation of CZTS using a 10% aqueous solution of ammonium fluoride. The effects of the chemical treatment were studied on the leakage current, charge transport measured as the electron mobility-lifetime (µτ) product, and the spectral resolution measured as the full-width at half-maximum (FWHM) of specific peaks. After passivation, the leakage current increased and began to decrease towards pre-passivation levels. The energy resolutions were recorded for eight applied voltages between −35 V and −200 V. The results showed an average of 25% improvement in the detector’s energy resolution for the 59.6 keV gamma peak of Am-241. The electron µτ product was unchanged at 2 × 10⁻³ cm²/V. These results show that ammonium fluoride is effective for chemical passivation of CZTS detectors.

Wide bandgap semiconductor materials capable of detecting X-rays and gamma-rays at room temperature without cryogenic cooling have great advantages that include portability and wide-area deployment in nuclear and radiological threat defense. Additional major applications include medical imaging, spectroscopy, and astrophysics. Most current room-temperature ionizing radiation detector devices are fabricated from cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe). Cadmium zinc telluride selenide (CdZnTeSe or CZTS) can be grown with high crystal yield compared to CdTe and CdZnTe. Thus, CZTS has the advantage of lowering the cost of room-temperature nuclear detectors. Thick CdTe-based detectors are prone to the trapping of charge carriers, thus limiting energy resolution and efficiency. A Frisch-Grid configuration helps to solve this problem. This research is focused on optimizing the Frisch-grid configuration for a CZTS detector. The CZTS was grown by traveling heater method. Infrared images of the CZTS matrix largely showed the absence of tellurium inclusions. The resistivity of the CZTS obtained from a current-voltage plot is of the order of 1010 Ω.cm. The charge-transport characterized by measuring the electron mobility-lifetime product is 4.7 x 10-3 cm2/V. Detector resolution was measured for various Frischring widths. For a 4.8 × 4.9 × 9.7 mm3 detector, the best Frisch-ring widths were found to be 3-4 mm. A detector resolution of 1.35% full-width-at-half-maximum was obtained for the 3-mm width at -2300 V bias voltage for the 662-keV gamma peak of 137Cs. A resolution of 1.36% was obtained for the 4-mm width at -1800 V applied bias.

Radiation detectors have been fabricated from Cd_1-xZn_xTe crystals and their performance has been studied with respect their Cd_1-xZn_xTe surface preparation. Energy resolution, leakage current, resistivity, ohmicity as well as surface roughness of the detectors were measured and compared for various chemical treatments. Etching in lactic acid has been found to lead to better ohmic contract, a rougher surface and higher leakage current. Bromine is effective in removing the damaged layer and when added to 20 percent lactic acid in ethylene glycol leads to a lower leakage current and consequently a better energy resolution. The best detector performance was obtained with a two step treatment consisting of a standard etchant (5 percent Br in methanol) followed by 2 percent Br in'20 percent lactic acid in ethylene glycol'. The results clearly demonstrate the important of surface chemical treatments in the fabrication of Cd_1-xZn_xTe radiation detectors.

We studied two separate as-grown CdMnTe crystals by Infrared (IR) microscopy and Pockels effect imaging, and then developed an algorithm to analyze and visualize the electric field within the crystals' bulk. In one of the two crystals the size and distribution of inclusions within the bulk promised to be more favorable in terms of efficiency as a detector crystal. However, the Te inclusions were arranged in characteristic 'planes'. Pockels imaging revealed an accumulation of charges in the region of these planes. We demonstrated that the planes induced stress within the bulk of the crystal that accumulated charges, thereby causing non-uniformity of the internal electric field and degrading the detector's performance.