Post-growth Annealing of Cadmium Zinc Telluride Crystals for Room-Temperature Radiation Detectors

Yang

Nuclear Instruments and Methods in Physics Research Section A:

et al. 2015

a b s t r a c tBridgman-grown cadmium zinc telluride (CdZnTe or CZT) and cadmium manganese telluride (CdMnTe or CMT) crystals often have Te inclusions that limit their performances as X-ray-and gamma-raydetectors. We present here the results of post-growth thermal annealing aimed at reducing and eliminating Te inclusions in them. In a 2D analysis, we observed that the sizes of the Te inclusions declined to 92% during a 60-h annealing of CZT at 510 1C under Cd vapor. Further, tellurium inclusions were eliminated completely in CMT samples annealed at 570 1C in Cd vapor for 26 h, whilst their electrical resistivity fell by an order of 10 2 . During the temperature-gradient annealing of CMT at 730 1C and an 18 1C/cm temperature gradient for 18 h in a vacuum of 10 À 5 mbar, we observed the diffusion of Te from the sample, so causing a reduction in size of the Te inclusions. For CZT samples annealed at 700 1C in a 10 1C/cm temperature gradient, we observed the migration of Te inclusions from a lowtemperature region to a high one at 0.022 μm/s. During the temperature-gradient annealing of CZT in a vacuum of 10 À 5 mbar at 570 1C and 30 1C/cm for 18 h, some Te inclusions moved toward the hightemperature side of the wafer, while other inclusions of the same size, i.e., 10 mm in diameter, remained in the same position. These results show that the migration, diffusion, and reaction of Te with Cd in the matrix of CZT-and CMT-wafers are complex phenomena that depend on the conditions in local regions, such as composition and structure, as well as on the annealing conditions.

Section: Introductionmentioning

confidence: 99%

Post-growth annealing of Bridgman-grown CdZnTe and CdMnTe crystals for room-temperature nuclear radiation detectors

Yang

Nuclear Instruments and Methods in Physics Research Section A:

et al. 2015

“…This is close to a reduction of one order of magnitude in the resistivity. In CdZnTe annealed at 670 C for 50 hours in Cd vapor, it was reported that the resistivity of the material was reduced up to five orders of magnitude [15]. The reasons for these observations are changes caused by the annealing processes to the concentrations of deep-level Te anti-sites, Cd interstitials, and Cd vacancies, that are responsible for the high resistivity of CdZnTe [15]- [17], and in CdMnTe.…”

Section: Resultsmentioning

confidence: 99%

“…In CdZnTe annealed at 670 C for 50 hours in Cd vapor, it was reported that the resistivity of the material was reduced up to five orders of magnitude [15]. The reasons for these observations are changes caused by the annealing processes to the concentrations of deep-level Te anti-sites, Cd interstitials, and Cd vacancies, that are responsible for the high resistivity of CdZnTe [15]- [17], and in CdMnTe. For CdZnTe annealed in Cd vapor, it was suggested by Yang et al [13] that the electrical compensation was lost due to extra Cd interstitials from the Cd vapor, thus resulting in shifting of the Fermi level towards the bottom of the conduction band.…”

Section: Resultsmentioning

confidence: 99%

“…The resistivity of CdMnTe crystals could be increased during crystal growth by doping the material with indium [1]. The problem of reduction in resistivity after annealing CdZnTe in Cd vapor could be resolved by annealing in a combination of Cd-rich and Zn-rich atmosphere [15]. Thus, it will be worth investigating the annealing of CdMnTe wafers in a combination of Cd and Mn vapors.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Thermal Annealing of CdMnTe Material Being Developed for Nuclear Radiation Detection Applications

Adams¹,

Agbalagba²,

Jow³

et al. 2016

IOSR

Cadmium manganese telluride (CdMnTe) is one of the semiconductor materials with potential applications at room-temperature for nuclear and radiological detection. CdMnTe crystals grown by Bridgman technique are prone to tellurium inclusions and related defects that limit their performance as X-rays and gamma-rays detectors. The major reason for this is that they are grown in a tellurium-rich environment. These defects could trap charges that are generated by X-rays and gamma rays thereby degrading the charge transport properties of the detectors and reducing their carrier lifetime. This in turn leads to poor performance by the detector. One of the solutions to this problem is post-growth thermal annealing. In this paper we present experimental results of annealing a CdMnTe wafer at 720 o C and in cadmium vapor. The CdMnTe wafer and cadmium were sealed in a quartz ampoule at a vacuum of 10-5 mbar. We used a three-zone furnace that enabled us to adjust the three heating elements to get a flat region of 720 o C in the temperature profile where the wafer was annealed. Infrared transmission microscopy showed changes to the sizes and positions of the tellurium inclusions. There are reductions in the dimensions of the medium-size Te inclusions. Some Te inclusions were completely eliminated while others broke up to form much smaller inclusions. Current-voltage measurements showed that the resistivity of the CdMnTe wafer was reduced by 71 %, from 2.44 x 10 5 -cm to 7.17 x 10 4 -cm after annealing in Cd vapor.

“…Furthermore, the resistivity of CZT decreases with an increase in the dislocations. Yang et al [12] conducted thermal annealing under Zn-vapor after Cd-vapor annealing to determine the specific resistivity of CZT. Egarievwe et al [10] analyzed the thermal annealing conditions required to remove and reduce Te inclusions; they reported that long-term thermal annealing at a low temperature of 783 K is more effective in reducing thermal stresses and irregular Cd inclusions than short-term thermal annealing at a high temperature of ∼1,170 K.…”

Section: Introductionmentioning

confidence: 99%

Improvement of charge collection efficiency of the CdZnTe detectors by decreasing the Te inclusions

Choi¹,

Park²,

Chai³

2022

Mater. Res. Express

CdZnTe is a promising material for room-temperature radiation semiconductor detectors. However, their radiation response performance might be deteriorated owing to defects within the material such as Te inclusions. This study employs the Cd thermal annealing process to reduce the size of these Te inclusions. An ampoule containing Cd powder and CdZnTe was sealed under the vacuum conditions of 2.5 × 10−5 Torr for Cd-vapor annealing. Subsequently, the ampoule was annealed at 783 K for 64 h. An IR camera was used to observe the distribution of Te inclusions in the CdZnTe before and after annealing. As a second experiment, NH4F + H2O2 passivation was performed to suppress the increased leakage current due to Cd-vapor annealing. Then an 241Am radioisotope source was used to obtain a radiation response spectrum. The improved charge collection efficiency was about 35 %.