Showing papers by "Michael Fiederle published in 2006"
TL;DR: The Frisch-ring detector as discussed by the authors is a bar-shaped CZT crystal with a geometrical aspect ratio of /spl sim/1:2, the side surfaces of the detector are coated with an insulating layer followed by a metal layer deposited directly upon the insulator.
Abstract: The performance characteristics of Frisch-ring CdZnTe (CZT) detectors are described and compared with other types of CZT devices. The Frisch-ring detector is a bar-shaped CZT crystal with a geometrical aspect ratio of /spl sim/1:2. The side surfaces of the detector are coated with an insulating layer followed by a metal layer deposited directly upon the insulator. The simple design operates as a single-carrier device. Despite the simplicity of this approach, its performance depends on many factors that are still not fully understood. We describe results of testing several detectors fabricated from CZT material produced by different vendors and compare the results with numerical simulations of these devices.
62 citations
01 Oct 2006
TL;DR: In this paper, the Bridgman method was used to grow a single crystal with diameters of 25 and 75 mm. The structural quality of the crystals was constantly improved to increase the single crystalline areas.
Abstract: (Cd,Zn)Te crystals were grown from the melt by the Bridgman method with diameters of 25 and 75 mm. The material was doped with indium. The structural quality of the crystals was constantly improved to increase the single crystalline areas. These improvements reduced the number of grains in the 25 mm and 75 mm diameter, respectively. The grown material with 25 m diameter are nearly single crystal. The crystals were characterized by electrical and optical methods for evaluation of the relation of structural quality and material properties. By the optimization of the crystal growth a reduction of the etch pitch density down to 2 times 103 1/cm2 could be achieved. The resistivity of the crystals was in the range of 2 times 109 up to 5 times 1010 Omegacm The detector performance was tested with different radiation sources. The product of mobility-lifetime of charge carriers was 3 times 10-3 cm2/V. The energy resolution for different radiation energies were measured for detector thickness of 1 mm and 10 mm.
21 citations
TL;DR: In this article, four CdTe ingots with gradually increased concentration of the Sn impurity have been grown by the vertical gradient freeze method and were characterized with glow discharge mass spectroscopy, photo-induced current transient spectrograms, resistivity, photoconductivity, and photoluminescence techniques.
Abstract: Four CdTe ingots with gradually increased concentration of the Sn impurity have been grown by the vertical gradient freeze method and were characterized with glow discharge mass spectroscopy, photoinduced current transient spectroscopy, resistivity, photoconductivity, and photoluminescence techniques. It was shown that the Sn impurity strongly influences resistivity and photoconductivity of the material. Concentration of Sn must be higher than the total concentration of residual acceptors to reach strong compensation. The middle-gap donor level pins the Fermi-level. Photoconductive high resistivity material can be prepared with Sn concentrations in the melt in the range 1018–1019 cm−3. In total, 6 electron traps and 3 hole traps were identified in the band gap by several complementary techniques.
13 citations
01 Oct 2006
TL;DR: In this paper, composite, polycrystalline, semiconductor, hexagonal BN alone or mixed with B4C or BMg2 and cubic LiF were embedded in an insulating matrix which acts as a binder and tested as alpha particle and neutron detectors.
Abstract: Composite, polycrystalline, semiconductor, hexagonal BN alone or mixed with B4C or BMg2 and cubic LiF were embedded in an insulating matrix which acts as a binder and tested as alpha particle and neutron detectors. The boron containing semiconductors have the natural abundance of 10B which is ~20%. In the case of LiF is the natural content of 6Li only 7.4%. The matrix binder further reduces the contents of 10B and 6Li to about one half. For alpha particles from a 241Am alpha source of ~105 cm-2s-1, 5.5 MeV gives the detector a wide peak in the spectrum. In the case of the thermal neutron detection, if the sources are very weak of only ~100 cm-2sec-1, the neutron counting is possible by subtracting the total signal from the noise. The resulting a signal to noise (S/N) ratio is of only ~2 and one needs a larger collection time of hours for a larger number of pulses to be collected. With a source of a higher neutron flux such as a nuclear reactor, which can offer flux of 107 cm-2s-1, is the S/N ratio of ~33. LiF composites with only 3.7% of 6Li could also detect very weak neutron sources, but the very low amount of 6Li produced a S/N ratio of ~1.4. Compared with widely used 3He detectors is the thermal neutron detection efficiency of the BN and LiF based detectors significantly higher for the same sizes of detectors. Even at a pressure of 3 atmospheres of an inch in diameter 3He detector is the detection efficiency 64% compared with ~72% of a 1 mm thick composite BN detector. Results of enriched 6LiF and mixed BN composite detector measurements with stronger neutron sources will be also reported.
4 citations
01 Oct 2006
TL;DR: In this article, 100 mum thick films of CdTe were grown on semi-insulating (100) GaAs substrates by physical vapor transport (PVT) in a modified molecular beam epitaxy facility.
Abstract: 100 mum thick films of CdTe were grown on semi-insulating (100) GaAs substrates by physical vapor transport (PVT) in a modified molecular beam epitaxy facility. The grown layers were highly oriented as revealed from X-ray pole figure measurements. Temperature- and intensity-dependent photoluminescence measurements were taken before and after the chemical removal of the substrate to determine the effect of the GaAs substrate and to estimate the crystallographic quality of the layers. Current-voltage characteristics were performed to obtain the resistivity of the layers with 108 Omegacm.
4 citations