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The Faraday effect in Cd{sub 0.57}Mn{sub 0.43}Te in high magnetic field

Description: The experimental results of Faraday rotation (FR) measurements in dilute magnetic semiconductors in high magnetic field are presented (Dirac Series--Los Alamos). The magnetic field is produced by an explosive-driven flux-compression generator (150 T). Measurements have been carried with samples of Cd{sub 1{minus}x}Mn{sub x}Te with x = 0.43 using 633 nm light at liquid helium temperature. The FR increases in such samples when the magnetic field exceeds 60 T. Interband exchange interaction and the direct influence of the external magnetic field on the exchange interaction must be considered to interpret the experimental results.
Date: March 26, 1997
Creator: Platonov, V.V.; Tatsenko, O.M. & Bykov, A.I.
Partner: UNT Libraries Government Documents Department

Pressure Effects on Magneto-Optical Properties in Cadmium Telluride/(Cadmium, Manganese) Telluride Single Quantum Well with High Manganese Concentration

Description: The pressure effect on the magnetic field induced type I-type II transition is studied in a CdTe/Cd<sub>1-x</sub>Mn<sub>x</sub>Te (x=0.24) single quantum well (SQW). Photoluminescence (PL) measurements under hydrostatic pressures up to 1.07 GPa and long pulsed magnetic fields up to 60 T with a pulse duration of 2 sec are reported. The pressures were generated in a plastic diamond anvil cell (DAC). A bend toward lower energies (additional red shift) is observed above 28.5 T in magnetic field dependence of the exciton energy for a 13 Aring thick quantum well. We attribute this red shift to a phenomenon preceding the type I-type II transition after a comparison with a simple quantum mechanical calculation. The onset field of the additional red shift increases by 3.4 T by applying a pressure of 1.07 GPa. Spin-spin coupling between the exciton and the Mn ion in the interface region is also investigated and found to be enhanced by pressure.
Date: November 9, 1998
Creator: Yokoi, H.; Tozer,S.; Kim, Y.; Rickel, D.; Kakudate, Y.; Usuba, S. et al.
Partner: UNT Libraries Government Documents Department

Effect of chemical etching on the surface roughness of CdZnTe and CdMnTe gamma radiation detectors

Description: Generally, mechanical polishing is performed to diminish the cutting damage followed by chemical etching to remove the remaining damage on crystal surfaces. In this paper, we detail the findings from our study of the effects of various chemical treatments on the roughness of crystal surfaces. We prepared several CdZnTe (CZT) and CdMnTe (CMT) crystals by mechanical polishing with 5 {micro}m and/or lower grits of Al{sub 2}O{sub 3} abrasive papers including final polishing with 0.05-{micro}m particle size alumina powder and then etched them for different periods with a 2%, 5% Bromine-Methanol (B-M) solution, and also with an E-solution (HNO{sub 3}:H{sub 2}O:Cr{sub 2}O{sub 7}). The material removal rate (etching rate) from the crystals was found to be 10 {micro}m, 30 {micro}m, and 15 {micro}m per minute, respectively. The roughness of the resulting surfaces was determined by the Atomic Force Microscopy (AFM) to identify the most efficient surface processing method by combining mechanical and chemical polishing.
Date: August 11, 2008
Creator: Hossain,A.; Babalola, S.; Bolotnikov, A.E.; Camarda, G.S.; Cui, Y.; Yang, G. et al.
Partner: UNT Libraries Government Documents Department

CdMnTe in X-ray and Gamma-ray Detection: Potential Applications

Description: CdMnTe can be a good candidate for gamma-ray detection because of its wide band-gap, high resistivity, and good electro-transport properties. Further, the ability to grow CMT crystals at relatively low temperatures ensures a high yield for manufacturing detectors with good compositional uniformity and few impurities. Our group at Brookhaven National Laboratory is investigating several CMT crystals, selecting a few of them to make detectors. In this paper, we discuss our initial characterization of these crystals and describe our preliminary results with a gamma-ray source.
Date: August 11, 2008
Creator: Cui,Y.; Bolotnikov, A.; Hossain, A.; Camarda, G.; Mycielski, A.; Yang, G. et al.
Partner: UNT Libraries Government Documents Department

High hydrostatic pressure effects on the exciton spin states in CdTe/Cd{sub 1-x}Mn{sub x}Te single quantum wells

Description: Photoluminescence (PL) was measured in a CdTe/Cd{sub 0.76}Mn{sub 0. 24}Te single quantum well structure under hydrostatic pressure up to 2.68 GPa and magnetic fields up to 30 T at 4.2 K. Pressure coefficients of exciton energies were found to be well width dependent. Magneto-PL experiments revealed negative pressure dependence of N{sub 0}({alpha}-{beta}) in barriers and saturation of T{sub 0} by the pressure.
Date: October 1, 1996
Creator: Yokoi, H.; Kakudate, Y.; Schmiedel, T.; Tozer, S.; Jones, E. D.; Takeyama, S. et al.
Partner: UNT Libraries Government Documents Department

Investigations of Cadmium Manganese Telluride Crystals for Room-Temperature Radiation Detection

Description: Cadmium manganese telluride (CMT) has high potential as a material for room-temperature nuclear-radiation detectors. We investigated indium-doped CMT crystals taken from the stable growth region of the ingot, and compared its characteristics with that from the last-to-freeze region. We employed different techniques, including synchrotron white-beam X-ray topography (SWBXT), current-voltage (I-V) measurements, and low-temperature photoluminescence spectra, and we also assessed their responses as detectors to irradiation exposure. The crystal from the stable growth region proved superior to that from the last-to-freeze region; it is a single-grain crystal, free of twins, and displayed a resistivity higher by two orders-of-magnitude. The segregation of indium dopant in the ingot might be responsible for its better resistivity. Furthermore, we recorded a good response in the detector fabricated from the crystal taken from the stable growth region; its ({mu}{tau}){sub e} value was 2.6 x 10{sup -3} cm{sup 2}/V, which is acceptable for thin detectors, including for applications in medicine.
Date: October 6, 2009
Creator: Yang, G.; Bolotnikov, A.; Camarda, G.; Cui, Y.; Hossain, A.; Kim, K. et al.
Partner: UNT Libraries Government Documents Department

Cadmium Manganese Telluride (Cd1-xMnxTe): A potential material for room-temperature radiation detectors

Description: Cadmium Manganese Telluride (CdMnTe) recently emerged as a promising material for room-temperature X- and gamma-ray detectors. It offers several potential advantages over CdZnTe. Among them is its optimal tunable band gap ranging from 1.7-2.2 eV, and its relatively low (< 50%) content of Mn compared to that of Zn in CdZnTe that assures this favorable band-gap range. Another important asset is the segregation coefficient of Mn in CdTe that is approximately unity compared to 1.35 for Zn in CdZnTe, so ensuring the homogenous distribution of Mn throughout the ingot; hence, a large-volume stoichiometric yield is attained. However, some materials issues primarily related to the growth process impede the production of large, defect-free single crystals. The high bond-ionicity of CdMnTe entails a higher propensity to crystallize into a hexagonal structure rather than to adopt the expected zinc-blend structure, which is likely to generate twins in the crystals. In addition, bulk defects generate in the as-grown crystals due to the dearth of high-purity Mn, which yields a low-resistivity material. In this presentation, we report on our observations of such material defects in current CdMnTe materials, and our evaluation of its potential as an alternative detector material to the well-known CdZnTe detectors. We characterized the bulk defects of several indium- and vanadium-doped Cd1-xMnxTe crystals by using several advanced techniques, viz., micro-scale mapping, white-beam x-ray diffraction/reflection topography, and chemical etching. Thereafter, we fabricated some detectors from selected CdMnTe crystals, characterized their electrical properties, and tested their performance as room-temperature X- and gamma-ray detectors. Our experimental results indicate that CdMnTe materials could well prove to become a viable alternative in the near future.
Date: July 11, 2010
Creator: Hossain, A.; Cui, Y.; Bolotnikov, A.; Camarda, G.; Yang, G.; Kim, K-H. et al.
Partner: UNT Libraries Government Documents Department

Charge transport properties of CdMnTe radiation detectors

Description: Growth, fabrication and characterization of indium-doped cadmium manganese telluride (CdMnTe)radiation detectors have been described. Alpha-particle spectroscopy measurements and time resolved current transient measurements have yielded an average charge collection efficiency approaching 100 %. Spatially resolved charge collection efficiency maps have been produced for a range of detector bias voltages. Inhomogeneities in the charge transport of the CdMnTe crystals have been associated with chains of tellurium inclusions within the detector bulk. Further, it has been shown that the role of tellurium inclusions in degrading chargecollection is reduced with increasing values of bias voltage. The electron transit time was determined from time of flight measurements. From the dependence of drift velocity on applied electric field the electron mobility was found to be n = (718 55) cm2/Vs at room temperature.
Date: April 11, 2012
Creator: K., Kim; Rafiel, R.; Boardman, M.; Reinhard, I.; Sarbutt, A.; Watt, G. et al.
Partner: UNT Libraries Government Documents Department

High efficiency cadmium and zinc telluride-based thin film solar cells

Description: Polycrystalline Cd{sub 1-x}Zn{sub x}Te and Cd{sub 1-x}Mn{sub x}Te films with a band gap of 1.7 eV were successfully grown on glass/SnO{sub 2}/CdS substrates by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD), respectively. Polycrystalline Cd{sub 1-x}Zn{sub x}Te films grown by MBE resulted in uniform composition and sharp interfaces. However, polycrystalline Cd{sub 1-x}Mn{sub x}Te films grown by MOCVD showed nonuniform compositions and evidence of manganese accumulation at the Cd{sub 1-x}Mn{sub x}Te/CdS interface. We found that manganese interdiffuses and replaces cadmium in the CdS film. By improving the CdTe/CdS interface and, thus, reducing the collection function effects, the efficiency of the MOCVD CdTe cell can be improved to about 13.5%. MBE-grown CdTe cells also produced 8%--9% efficiencies. The standard CdTe process was not optimum for ternary films and resulted in a decrease in the band gap. Recent results indicate that CdCl{sub 2} + ZnCl{sub 2} chemical treatment may prevent the band-gap reduction, and that chromate etch (rather than bromine etch) may provide the solution to contact resistance in the ternary cells.
Date: October 1, 1990
Creator: Rohatgi, A.; Summers, C.J.; Erbil, A.; Sudharsanan, R. & Ringel, S. (Georgia Inst. of Tech., Atlanta, GA (USA). School of Electrical Engineering)
Partner: UNT Libraries Government Documents Department