Bridgman-Grown (Cd,Mn)Te and (Cd,Mn)(Te,Se): A Comparison of Suitability for X and Gamma Detectors

This study explores the suitability of (Cd,Mn)Te and (Cd,Mn)(Te,Se) as room-temperature X-ray and gamma-ray detector materials, grown using the Bridgman method. The investigation compares their crystal structure, mechanical and optical properties, and radiation detection capabilities. Both crystals can yield large-area single crystal samples measuring approximately 30 × 30 mm2. In low-temperature photoluminescence analysis, both materials showed defect states, and annealing in cadmium vapors effectively eliminated donor–acceptor pair luminescence in (Cd,Mn)Te but not in (Cd,Mn)(Te,Se). Moreover, harder (Cd,Mn)(Te,Se) exhibited a higher etch pit density compared to softer (Cd,Mn)Te. X-ray diffraction examination revealed uniform lattice constant distribution in both compounds, with variations at a part per million level. (Cd,Mn)Te crystals demonstrated excellent single crystal properties with narrower omega scan widths, while (Cd,Mn)(Te,Se) exhibited a high contribution of block-like structures with significantly larger misorientation angles. Spectroscopic evaluations revealed better performance of a pixelated (Cd,Mn)Te detector, in comparison to (Cd,Mn)(Te,Se), achieving a mean full width at half maximum of 14% for the 122 keV gamma peak of Co-57. The reduced performance of the (Cd,Mn)(Te,Se) detector may be attributed to deep trap-related luminescence or block-like structures with larger misorientation angles. In conclusion, Bridgman-grown (Cd,Mn)Te emerges as a more promising material for X-ray and gamma-ray detectors when compared to (Cd,Mn)(Te,Se).

The addition of selenium to (Cd,Mn)Te increased the compound's hardness.However, (Cd,Mn)(Te,Se) exhibited one order of magnitude higher etch pit density compared to (Cd,Mn)Te.
Photoluminescence analysis at low temperatures revealed the presence of defect states in both materials, characterized by shallow and deep donor-acceptor pair transitions (DAP).Annealing in cadmium vapors effectively eliminated DAP luminescence in (Cd,Mn)Te but not in (Cd,Mn)(Te,Se).Spectroscopic performance assessments indicated that the (Cd,Mn)Te detector outperformed the (Cd,Mn)(Te,Se) detector in responding to a Co-57 source.The reduced performance in the latter case may be attributed to either the presence of a deep trap related to deep DAP luminescence, minimally affected by annealing, or the dominant presence of block-like structures in the samples, as indicated by X-ray
In our laboratory, we regularly conduct investigations on high resistivity (Cd,Mn)Te, which material did we propose for X-ray and gamma detectors [40] and which has proven to be a promising Xray and gamma radiation detector [41].Furthermore, for crystal growth, we employ the Bridgman method, enabling the relatively fast production of large (≥ 1.5 in.) crystals with a crystal growth rate of several mm per hour, as compared to methods such as the traveling heater method (THM), where the crystal growth rate is 3-5 mm per day [42,43].Our motivation to study compounds alloyed with selenium, specifically (Cd,Mn)(Te,Se), stemmed from the literature findings.In the field of X-ray and gamma-ray detectors, there is currently a heated debate regarding the use of selenium-alloyed CdTe crystals.In this article, we present new data and express our position on this matter.
According to previous research on (Cd,Zn)Te and (Cd,Zn)(Te,Se) [8,44], the presence of selenium plays a crucial role in inhibiting the development of sub-grain boundary networks, and increases the hardness of the quaternary material (Cd,Zn)(Te,Se).Additionally, selenium significantly reduces the concentration of tellurium inclusions [43].Subsequently, it can be inferred from UV-Vis absorbance data that changes in the bandgap values along the growth direction (reduced length of 0.1 to 0.9 of the ingot) in Cd 0.9 Zn 0.1 Te crystals amount to 31 meV, whereas in Cd 0.9 Zn 0.1 Te 0.98 Se 0.02 , they are only 21 meV [45].This indicates that in (Cd,Zn)(Te,Se) crystals, a more uniform difference of bandgap values along the growth direction is achieved due to reduced segregation effects.A homogeneous distribution of the energy bandgap in crystals is important because it influences the distribution of other properties, such as resistivity and absorption edge [39].
In this work, instead of the more commonly investigated (Cd,Zn)Te, we utilize (Cd,Mn)Te due to several advantages of Mn-alloyed CdTe over Zn-alloying.Firstly, the segregation coefficient of Mn in CdTe is close to unity, specifically 0.95 [46], whereas the segregation coefficient of Zn in CdTe is 1.3 [47].This results in a more homogeneous distribution of Mn in CdTe, whereas in (Cd,Zn)Te, there is a higher concentration of Zn at the first-to-freeze part of the ingot.However, there are reports that the addition of Se to (Cd,Zn)Te reduces Zn segregation in the ingot, and a homogeneous chemical composition can be achieved in the axial and radial directions in 90% of the volume of (Cd,Zn)(Te,Se) crystals obtained by the THM method [43].Secondly, for a detector to operate at room temperature, the semiconductor material should have an appropriate energy bandgap, ranging from 1.5 to 2.2 eV [39].
Achieving the desired energy bandgap involves adding a larger quantity of Zn to CdTe in comparison to introducing Mn to CdTe.This is because the energy bandgap of (Cd,Zn)Te undergoes a slower transformation with the addition of Zn, changing at a rate of 6.7 meV per atomic percent of Zn [48].
Conversely, introducing Mn to CdTe alters the energy bandgap by 13 meV for every atomic percent of Mn [49].Furthermore, the addition of Se to CdTe reduces the energy bandgap in crystals typically chosen for X-ray and gamma-ray detector applications, specifically those containing less than or equal to 2% Se.
In CdTe 1−x Se x crystals, the energy gap decreases as x increases, at a rate of approximately 4 meV per atomic percent of Se for x ≤ 0.1.This rate decreases for 0.1 ≤ x ≤ 0.4, reaches its minimum at x ≈ 0.4, and then begins to increase as x continues to rise [50].This consideration is significant.Restricting the quantity of the third or fourth alloying component helps limit the formation of new defects within the crystal structure.Thirdly, it has been experimentally observed that larger grains can be obtained in (Cd,Mn)Te than in (Cd,Zn)Te, enabling the production of larger volume detector plates from such a crystal.
In this study, we investigate two compounds grown by the Bridgman method: (Cd,Mn)Te and (Cd,Mn)(Te,Se), and we compare their suitability for X-ray and gamma-ray detectors.The research involves examining the hardness and employing the etch pit density technique to determine if harder materials display fewer detrimental sub-grain boundaries and their networks.We conducted microstructure imaging using infrared microscopy.Subsequently, we conduct a detailed characterization of the crystalline structure of selected large-surface-area single crystal samples, such as 30×30 mm 2 .We draw lattice constant and omega scan maps for these compounds.The photoluminescence of the as-grown samples is investigated, and by comparing the results with samples annealed in Cd and Se vapors, we discuss the presence of defects in the as-grown crystals.Finally, we present the energy spectrum from a Co-57 source recorded using our selected and optimized crystal.

Materials and methods
Crystals of Cd 1−x Mn x Te and Cd 1−x Mn x Te 1−y Se y were grown using the low-pressure Bridgman method, with x set at either 5% or 7%, and y at 2%.The growth process employed high-purity materials, specifically 7N Cd, 7N Te, 6N Mn, and 6N Se.These crystals had diameters of either 2 or 3 in.Hardness investigations were carried out on a Cd 0.95 Mn 0.05 Te 0.98 Se 0.02 crystal as the primary sample, while Cd 0.93 Mn 0.07 Te 0.98 Se 0.02 crystals were utilized in other measurements.In the context of (Cd,Mn)Te crystals, those with a 5% Mn composition were consistently examined.The crystal growth process was performed under Te-rich conditions, involving the addition of 30 mg to 100 mg of extra Te per 100 g of material.For compensation, a co-doping of indium or vanadium was used.The concentration of indium was 1×10 17 cm −3 (for Cd 0.95 Mn 0.05 Te), or 5×10 16 cm −3 (for Cd 0.95 Mn 0.05 Te 0.98 Se 0.02 ), or 1×10 14 cm −3 (for Cd 0.93 Mn 0.07 Te 0.98 Se 0.02 ), while that of vanadium was 1×10 13 cm −3 for all crystals.To visualize the grain boundaries in the crystals, they were etched using the Durose solution [51].Next, the samples were mechano-chemically polished using a 2% bromine solution in methanol and ethylene glycol.
Annealing processes were carried out for 168 hours in vacuum-sealed quartz ampoules in Cd vapors at the temperature of 800 °C or in Se vapors at 350 °C.
Mechanical properties were tested by measuring the microhardness of the polished samples on the cadmium side, i.e. (111)A plane, using a Vickers indenter with a load of 50 g for 15 s.For the purpose of comparison, one CdTe crystal, one Cd(Te,Se) crystal with a 5% Se composition, and two (Cd,Zn)Te crystals with 5% and 12% Zn, respectively, were also utilized in these studies.
The etch pit density was examined using the E-Ag1 Inoue solution, which consists of 0.5 parts AgNO 3 and 10 parts solution E. Solution E is composed of 5 parts HNO 3 , 10 parts H 2 O, and 2 parts K 2 Cr 2 O 7 [52].The etching time was equal to 90 s.The (111)A side was observed.For microscopic observations, an Olympus BX51 microscope equipped with an Olympus XC10 CCD camera was utilized, either in reflection or infrared transmission mode, depending on the purpose.
In the diffraction studies, a high-resolution Philips X'Pert MRD diffractometer was employed, featuring a monochromatized source of CuK α1 radiation (λ = 1.5406Å) and further equipped with a homemade mask and slit.This homemade mask was responsible for reducing the dimensions of the X-ray beam to 0.5×1.0mm 2 , enabling the collection of diffraction data from the samples point by point and line by line.X-ray scans were performed on sample areas measuring 18×20 mm 2 .Bragg angle measurements were carried out, with a focus on the 333 reflex, to generate maps of lattice constant variations within the samples.Omega curve measurements, depicting the intensity of the diffracted beam on the crystal as a function of the omega angle, ω, which is the angle between incident X-ray beam and the surface of the sample, were conducted to create delta omega maps and full width at half maximum (FWHM) maps.Both Bragg angle and omega curve measurements were carried out with a step size of 1 mm for X and 2 mm for Y.
Omega curve measurements were conducted in either double-axis mode (DA) or triple-axis mode (TA).In the TA mode, an analyzer was utilized to enhance the resolution, reducing it from 18 arcsec (DA) to 8 arcsec (TA), as determined by a measurement of a Si(111) reference sample.In the DA mode the detector was fully opened.The omega angle measured with the analyzer is referred to as ω TA , while without the analyzer, it is denoted as ω DA .
The omega angle was determined at the peak of the curve or, in cases of multiple peaks, at the extreme peaks.Delta omega, ∆ω, was then calculated by subtracting these values from each other.In instances where only one peak was present on the curve, it was assumed that delta omega equaled zero.This data was utilized to generate delta omega maps.
The photoluminescence (PL) studies were carried out on the cleaved samples and the excitation energy was equal to 2.33 eV.The PL spectra were obtained at 5 K in a continuous flow cryostat with a photomultiplier.
The spectroscopic response at room temperature of the pixelated detectors was checked using a Co-57 source and the Spectroscopic Pixel Mapping machine by Eurorad.For this purpose, electrical contacts, made of a gold-palladium alloy in an 80:20 ratio, were deposited using the Quorum Sputter Coater Q150T.Pixels on the anode, which crystallographically represents the cadmium side, were produced using the photolithography method.The cathode remained planar.The detector received radiation from the cathode side and was maintained at a bias voltage of −400 V.The shaping time was set to 1 μs.

Results and discussion
In our laboratory, by properly doping with In, V, or both In and V, we can obtain (Cd,Mn)Te and (Cd,Mn)(Te,Se) crystals with average resistivity on the order of 10 9 Ω cm and a mobility-lifetime product on the order of 10 −3 cm 2 V −1 [41].We are also capable of producing large single crystal plates, as depicted in Fig. 1.Fig. 1a shows a sliced (Cd,Mn)Te plate, which was cut perpendicular to the growth axis from a 2-in.ingot, ground, and then etched with Durose solution to reveal grain boundaries.It is evident that the plate is monocrystalline.On the other hand, Fig. 1b shows a (111)-oriented polished plate that has been prepared for detector fabrication, i.e., for the application of electrical contacts.This plate is also monocrystalline and has large dimensions of approximately 30×30 mm 2 .Visual examination of the obtained crystals yielded satisfactory results.These results provide an excellent basis for further research, as the field of room-temperature X-ray and gamma semiconductor detectors demands high-resistivity (>10 9 Ω cm), defect-free, monocrystalline, large (more than 5-8 cm 2 ), and sufficiently thick (>3 mm) plates for effective operation, i.e., to ensure effective interactions between high-energy radiation and the detector material.In Subsection 3.2, we will present more advanced studies on the crystal structure.

Hardness
The influence of Mn and Se additives on the hardness of the formed CdTe-based compounds was examined.As shown in Fig. 2, a five percent addition of manganese or selenium to CdTe increases the hardness of the compound, with the influence of selenium being stronger.The hardness of CdTe alloyed with manganese (5%) and selenium (2%), i.e., (Cd,Mn)(Te,Se) compound, falls between the hardness of (Cd,Mn)Te (Mn 5%) and Cd(Te,Se) (Se 5%).For comparison, we also investigated two crystals of (Cd,Zn)Te with different Zn contents, namely 5% and 12%.The crystals with Zn exhibited the highest hardness among all the samples examined, and a higher Zn content resulted in increased hardness, which is consistent with the literature data [53].In the comparison, we included the hardness result for CdTe crystal both alloyed with Zn and Se, measured by other authors [11].The addition of 2% Se to (Cd,Zn)Te further hardened the material.The result maintains the same trend.Despite the greater hardness of (Cd,Zn)Te crystals, the focus of this study lies on (Cd,Mn)Te crystals because, as mentioned in Section 1, it is easier to attain larger grains in the latter.
The addition of some additional elements to the CdTe matrix, like Mn, Se, or Zn, alters its structure.These changes can make it more challenging for atoms and dislocations to move within the lattice, resulting in material hardening.Additionally, by introducing an additional element to the CdTe matrix, the bond lengths, like Cd-Te, Mn-Te, Zn-Te, Cd-Se, are changed, leading to the formation of strong and stable atomic connections [54].These bonds can hinder atom movement and impede material deformation.
Fig. 2. Hardness of the selected CdTe-based compounds measured on the (111)A cadmium side.

Etch pit density
A test was conducted to examine whether higher hardness values translate into a smaller population of sub-grain boundaries, which are often encountered in CdTe-based compounds produced using the Bridgman method and pose a significant issue in detector performance.Typically, sub-grain boundaries are investigated using the White Beam X-ray Diffraction Tomography method [8,[55][56][57][58][59].We employed an etching method to reveal etch pits using the Inoue solution, as the Nakagawa solution [60] yielded no results on our samples.Sub-grain boundaries, which have a small misorientation angle, are formed by dislocation clusters.Sub-grain sizes are on the order of hundreds of micrometers [56].Hence, if we observe any clusters of etch pits, which form on the crystal surface at the location where dislocations initiate, it could suggest the presence of sub-grain boundaries in the investigated crystal.The formation of etch pits related to dislocations occurs due to the interplay between the stress field caused by dislocations and the surface energy [61].The CdTe and (Cd,Mn)(Te,Se) samples exhibit a high density of etch pits, on the order of 10 5 cm −2 .
However, in the CdTe sample, the average size of etch pits is significantly larger compared to (Cd,Mn)(Te,Se), measuring approximately 40 μm and 5 μm, respectively.The density of etch pits is the lowest in the (Cd,Mn)Te sample, namely 10 4 cm −2 , and their size ranges between 3 and 5 μm.The larger size of the etch pits in CdTe than in (Cd,Mn)Te and (Cd,Mn)(Te,Se) may be attributed to the larger stress fields generated by dislocations in that region.Observations of the etch pits revealed their uniform distribution, without the formation of clusters resembling small-angle boundaries.This suggests the absence of sub-grain boundaries in each of the investigated compounds, although this cannot be conclusively determined by this method.However, it is certain that the (Cd,Mn)Te sample exhibited the smallest dislocation density on its surface and demonstrated the best quality among the samples examined.

Lattice constant
We conducted a lattice constant mapping on monocrystalline samples of (Cd,Mn)Te (Fig. 4a) and (Cd,Mn)(Te,Se) (Fig. 4b).The lattice constant changes, denoted in Fig. 4 as ∆a/<a>, are expressed as in Eq. 1: where: alocal value of lattice constant, <a>the arithmetic mean value of all local values a determined at different locations along the sample.
The average value of lattice constant for Cd 0.95 Mn 0.05 Te is 6.47658 Å, and for Cd 0.93 Mn 0.07 Te 0.98 Se 0.02 is 6.46411 Å, both with a standard deviation of 0.00008 Å.In Fig. 4

Presence of blocks/grains and their mutual misorientation
Delta omega maps were prepared to check the presence of blocks/grains in our samples and, if they were present, to determine their mutual misorientation.Delta omega map of the (Cd,Mn)Te sample is depicted in Fig. 5a.A non-zero delta omega value indicates the presence of blocks (consisting of two or more) that exhibit misorientation relative to each other, with the delta omega value representing the maximum misorientation between these blocks.Conversely, a delta omega value of zero signifies that, at that specific measurement point, only a single peak was recorded, indicating the absence of blocks or grains.
In Fig. 5a, a delta omega value of zero is found in the majority of measurement points.Out of the 220 points on the delta omega map, only 5 points show an omega scan curve with two peaks, indicating the presence of two misoriented blocks.This indicates that in 215 measurement points, which accounts for approximately 98% of the 18×22 mm 2 area of this (Cd,Mn)Te sample, a single peak was recorded, implying the absence of grains or blocks with different orientations.Consequently, it can be concluded that a well-defined monocrystal is observed within the resolution limits of our measurement method.
The map in Fig. 5b illustrates how the intensity (signal strength) of specific omega angles is varied in this (Cd,Mn)Te sample.This map was created using data from 20 omega curves collected at 20 points in the sample, along the Y = −8 line, with an X step of 1 mm.The aim of this was to visualize variations in the omega angle at different points (X, −8) within the sample.Here, the value of the omega angle should be determined based on the angle corresponding to the highest intensity, which signifies the peak of the signal.The choice of the Y = −8 line was motivated by the presence of several points with notably higher deviations, as clearly indicated in Fig. 5a, where the Y = −8 line is marked by a red dashed line.
In Fig. 5b, it is evident that the omega angle, depicted as points with the highest intensity, i.e., corresponding to the maximum of the omega curve, remains constant in the range from X = −10 to X = 0.5.At X = 0.5, a shift of the X-ray beam from one block (grain) to another is observed.Subsequently, from X = 2 to X = 9, the omega angle is once again maintained at a near-constant value.The maximum misorientation angle between these two blocks is measured at 50 arcsec.It can be observed that in the (Cd,Mn)Te sample, despite selecting a line along the Y-axis in the sample with poorer X-ray results for the creation of the map in Fig. 5b, the omega angles remain nearly constant.Fig. 6a depicts the delta omega map of a (Cd,Mn)(Te,Se) sample.This map was also measured in triple axis mode.In the case of the (Cd,Mn)(Te,Se) crystal, a higher number of measurement points with non-zero values of delta omega are observed, indicating the presence of multiple blocks or grains.
Furthermore, the maximum misorientation between these blocks, represented by the delta omega value, is significantly larger compared to (Cd,Mn)Te, on the order of 100 arcsec (with a maximum of 800 arcsec), whereas for (Cd,Mn)Te, it was on the order of 10 arcsec (with a maximum of 90 arcsec).
The changes of the intensity of omega angle values in the omega scans of a (Cd,Mn)(Te,Se) sample conducted along the Y = −10 line are depicted in Fig. 6b.In the case of the (Cd,Mn)(Te,Se) crystal, similar to (Cd,Mn)Te (Fig. 5b), the map was generated based on 20 omega scans along the Y-axis, and a Y line was chosen where a greater number of measurement points with higher (worse) delta omega values were encountered.Here, a significant dispersion of omega angle values is evident.Fig.6b is on the same angular scale as Fig. 5b.The variation in these values between the red areas from Fig. 6b, those with the highest intensity, is 720-1080 arcsec (0.2-0.3 degrees).Let us recall that in the worst location of the (Cd,Mn)Te sample, Y = −8, variations in the omega angle were at the level of 50 arcsec (Fig. 5b).
Although the (Cd,Mn)(Te,Se) sample etched with Durose's solution appeared to be monocrystalline to the naked eye, X-ray studies revealed the presence of misoriented blocks within it.This is clearly visible in Fig. 6a, where monocrystalline regions, preferred for X and gamma radiation detectors, are highlighted in white and represent a small portion of the sample.The majority of the sample consists of blocks, which are less desirable in the aforementioned application because crystal structure defects serve as scattering or recombination centers for charge carriers.
Omega scans for selected points X, Y: (−7, −6) and (6, −2) are presented in Fig. 6c and Fig. 6d, respectively.In Fig. 6c, four maxima can be observed, signifying a block-like or sub-grain structure of the sample.The FWHM value taken from the extreme maxima is 300 arcsec.Meanwhile, in Fig. 6d, a single, very narrow peak with an FWHM of 15 arcsec is seen, indicating a monocrystalline structure of the sample at that particular location.In this paper, we observed the same issues that our (Cd,Mn)(Te,Se) crystals had previously encountered [37].Although the sample appeared to be monocrystalline during visual observation of the Durose-etched surface, revealing no grains and twins, it is, in fact, composed of misoriented blocks with a significant mosaic component (areas with a surface on the order of square millimeters).structure of the sample at that particular location.It is worth noting that the scale of the X axis for Fig. 6c and d is identical.In the (Cd,Mn)(Te,Se) sample, there are areas with block-like structures (Fig. 6c) as well as perfectly monocrystalline regions (Fig. 6d).
According to Darwin's model [62], a monocrystal is composed of a mosaic (blocks) with sizes ranging from 10 nm to 1 µm, slightly misoriented with respect to each other.The angle of misorientation between blocks typically ranges from a few arcseconds to a few minutes, in exceptional cases a few degrees.These small-angle boundaries are formed by a set of dislocations.
Micro-mosaic is present in practically every crystal.However, delta omega maps of our (Cd,Mn)Te (Fig. 5a) and (Cd,Mn)(Te,Se) (Fig. 6a) samples indicate a significantly higher contribution of block-like structure in the second one.Furthermore, in the (Cd,Mn)(Te,Se) crystal, the maximum misorientation between the blocks, ∆ω TA , is 10 times larger than in the (Cd,Mn)Te crystal.Therefore, the results of omega scans suggest a more perfect crystalline structure in the crystal without selenium alloying, i.e., (Cd,Mn)Te.

FWHM of Omega Scans
Now, let us consider the (Cd,Mn)Te crystal once again.In Fig. 7a, a map of the FWHM obtained from the omega scans at consecutive points of the sample is presented.This map was obtained in tripleaxis mode.Several (five) points with worse (higher) FWHM values are located in the lower-right corner, which corresponds well to Fig. 5a, where the presence of two blocks was recorded in that area.Apart from these exceptions, in the monocrystalline region of the sample, the FWHM of the omega scan is consistently better than ~50 arcsec.
In Fig. 7b, a selected omega scan for the measurement point X = −1, Y = −6, chosen from the map in Fig. 7a, has been presented.When measured in double-axis (DA) mode, meaning without the use of an analyzer, the FWHM of this rocking curve is 38 arcsec.However, when an analyzer is employed, i.e., in triple-axis mode, the FWHM is reduced to 20 arcsec.
An FWHM map is not presented for the (Cd,Mn)(Te,Se) crystal because the omega scans resulted in curves with multiple maxima (indicating the presence of blocks/grains in the sample).Therefore, it is challenging to arbitrarily determine which FWHM value should be included in the map.
For comparison, high-resolution rocking curve measurements of THM-grown (Cd,Zn)(Te,Se) crystals resulted in an FWHM value of 30.8 arcsec, and no mosaic structure was observed [63].This outcome can be attributed to the THM method's slower growth rate compared to the Bridgman method, mentioned in Section 1, which leads to fewer structural defects and, consequently, the achievement of a low FWHM value.On the other hand, when examining rocking curve studies of Bridgman-grown crystals, a broad spectrum of reported FWHM values for omega scans in the case of (Cd,Zn)Te exists, ranging from 8 to over 400 arcsec [64][65][66].For as-grown (Cd,Mn)Te crystals, previous research has reported FWHM values of 68 arcsec [67] or 72 arcsec [68].In contrast, our (Cd,Mn)Te crystal demonstrates superior performance, featuring an FWHM value for the omega scan that is almost two times smaller (in double-axis mode).Our X-ray examinations suggest a better crystal structure in (Cd,Mn)Te crystals compared to (Cd,Mn)(Te,Se) crystals.The distribution of lattice constant in both samples was very good, exhibiting minimal changes at the ppm level.However, omega scans revealed a significant presence of block/grainlike structures in (Cd,Mn)(Te,Se) crystals, much higher than in (Cd,Mn)Te crystals, and displayed a higher degree of misorientation.Both X-ray studies and EPD (Etch Pit Density) measurements suggest that (Cd,Mn)Te crystals are more suitable for X-ray and gamma detectors compared to crystals with selenium addition.

Impact of grain boundaries and twins
The influence of grain boundaries and twins on the FWHM of the omega curve measurement was investigated in (Cd,Mn)Te crystals.Specifically for this purpose, a (Cd,Mn)Te plate with both grain boundary and twin was examined.Studying grain boundaries and twins is crucial in CdTe-based materials for X-ray and gamma-ray detectors because understanding the structure of grain boundaries and twins can lead to improvements in the detector manufacturing process and the quality of X-ray and gamma-ray radiation detection, including the energy resolution of the detector.

Photoluminescence of as-grown and annealed crystals
Fig. 10a and 10b depict low-temperature photoluminescence (PL) spectra of (Cd,Mn)Te and (Cd,Mn)(Te,Se) samples, respectively.These spectra exhibit common features with the PL spectra of (Cd,Zn)Te.In both the (Cd,Mn)Te and (Cd,Mn)(Te,Se) samples we investigated, we can identify excitonic luminescence, donor-acceptor transitions, and defect-related bands, similar to what is observed in (Cd,Zn)Te [39].
In both of the as-grown materials, there are excitonic transitions, including D 0 X (exciton bound to a neutral donor) and A 0 X (exciton bound to a neutral acceptor), as well as two donor-acceptor pair transitions (DAP).In some instances, these transitions are accompanied by their phonon replicas, with energies approximately 20 meV lower.Specifically, shallow (s) and deep (d) DAP transitions are located about 70 meV and 200 meV below the exciton lines, respectively.
Bridgman-grown (Cd,Mn)Te and (Cd,Mn)(Te,Se) crystals naturally exhibit a high concentration of Cd vacancies, which act as acceptors.This is a consequence of the insufficient Cd content at high temperature during crystal growth (~1100 °C), caused by the high partial pressure of Cd.To reduce the concentration of cadmium vacancies, we applied annealing to both crystals, with and without selenium, in a cadmium-rich environment.
Consequently, in (Cd,Mn)Te crystals, the intensity of the A 0 X and DAP s PL lines was reduced, and emission from a DAP d transition was eliminated, as demonstrated in Fig. 10a.Thus, it can be inferred that the concentration of acceptors is lower in the Cd-annealed sample compared to the as-grown one.
Previous studies have shown that annealing in Cd vapors effectively eliminates the PL peak associated with the DAP s transition in our (Cd,Mn)Te samples, as well (Figs. 9 and 10 in [71]).

Detector response
Finally, a comparison was made between the detector response of two materials, (Cd,Mn)Te and (Cd,Mn)(Te,Se).The performance of the detectors at room temperature was assessed using a Co-57 point source.An example image of a (Cd,Mn)Te pixelated detector, which was prepared in our laboratory, is shown in Fig. 11a.
Our as-grown (Cd,Mn)Te detector is capable of distinguishing 122 keV gamma-rays from Co-57 with an energy resolution ranging from 8% to 17%.The spectroscopic performance of a selected (Cd,Mn)Te detector pixel, featuring an FWHM of 14%, is presented in Fig. 11b.
Conversely, our (Cd,Mn)(Te,Se) detector only detects X-rays from Co-57 at 7 keV with an energy resolution of approximately 45%, along with a minor trace of gamma-rays at 14.

Conclusions
We conducted a comparative analysis of two CdTe-based compounds, (Cd,Mn)Te and (Cd,Mn)(Te,Se), both grown using the Bridgman method, focusing on their crystal structure, hardness, luminescence properties, and their effectiveness as X-ray and gamma-ray detectors.
X-ray examinations of visually identified monocrystalline samples revealed very uniform lattice constants in both crystals, with minimal variations at the ppm level.However, omega curve measurements unveiled a significant presence of block-like structures within (Cd,Mn)(Te,Se) crystals, resulting in delta omega values, corresponding to the maximum misorientation between blocks, on the order of 100 arcsec (with a peak at 800 arcsec).In contrast, (Cd,Mn)Te crystals exhibited nearly perfect monocrystalline structures, with block-like features observed in only 2% of the 18×20 mm 2 area.Additionally, the misorientation angles between blocks in (Cd,Mn)Te were approximately ten times smaller than those observed in the selenium-containing crystals.Etching the crystals with Inoue solution further emphasized this contrast, displaying one order of magnitude fewer etch pits in (Cd,Mn)Te compared to (Cd,Mn)(Te,Se).The study also highlighted the detrimental influence of grain boundaries and the negligible impact of twins on the crystal structure quality of our samples.
We find that (Cd,Mn)Te shows greater promise as a material for X-ray and gamma-ray detectors.
It exhibits the ability to distinguish 122 keV gamma-rays from a Co-57 source with an energy resolution of 8-17%.Conversely, our (Cd,Mn)(Te,Se) detectors exhibited poor responses to X-and gamma-rays, potentially due to the presence of a deep trap involved in DAP d luminescence, which cannot be eliminated through annealing in Cd vapors, unlike in the case of (Cd,Mn)Te.Additionally, the significant contribution of block-like structures in selenium-containing crystal samples, accompanied by notably larger misorientation angles between these blocks compared to (Cd,Mn)Te, may contribute to the bad performance.

Fig. 1 .
Fig. 1.The image of the single crystal (Cd,Mn)Te samples.(a) Crystal plate cut from the 2-in.ingot and

Fig. 3
Fig. 3 illustrates microscopic images of the ~(111)A surface of three investigated by us

Fig. 5 .
Fig. 5. Cd 0.95 Mn 0.05 Te results.(a) Delta omega map of Cd 0.95 Mn 0.05 Te in the triple axis mode.(b) The map of the intensity of omega values, ω TA , obtained from 20 omega scans conducted along the Y = −8 line, with a 1 mm X step.The Y = −8 line is marked in Fig. 5a with a red dashed line.

Fig. 6 .
Fig. 6.Cd 0.93 Mn 0.07 Te 0.98 Se 0.02 results.(a) Delta omega map of Cd 0.93 Mn 0.07 Te 0.98 Se 0.02 in the triple axis mode.(b) The map of the intensity of omega values, ω TA , obtained from 20 omega scans conducted along the Y = −10 line, with a 1 mm X step.(c) Omega scan for measurement point X, Y: (−7, −6).Four distinct

Fig. 9a displaysFig. 9 .
Fig.9adisplays an IR image of a twin in (Cd,Mn)Te.This twin is decorated with tellurium

Fig. 10 .
Fig. 10.Photoluminescence spectra at the temperature of 5 K. (a) Cd 0.95 Mn 0.05 Te sample.Annealing in Cd vapors eliminated the DAP d luminescence.(b) Cd 0.95 Mn 0.05 Te 0.98 Se 0.02 sample.Annealing in Cd or Se vapors did not eliminate the DAP s and DAP d luminescence.