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We investigated the influence of deep levels on the electrical transport properties of CdZnTeSe (CZTS) radiation detectors by comparing experimental data with numerical simulations based on the simultaneous solution of drift-diffusion and Poisson equations, including the Shockley-Read-Hall model of the carrier trapping. We determined the Schottky barrier heights and the Fermi level position from I-V measurements. We measured the time evolution of the electric field and the electrical current after the application of a voltage bias. We observed that the electrical properties of CZTS are fundamentally governed by two deep levels close to the mid-bandgap—one recombination and one hole trap. We show that the hole trap indirectly increases the mobility-lifetime product of electrons. We conclude that the structure of deep levels in CZTS is favorable for high electrical charge transport. [ABSTRACT FROM AUTHOR]

Because of its excellent opto-electronic properties, CdZnTe (CZT) has been the material of choice for x- and gamma-ray detectors operable at room temperature. CZT is the leading commercially available room-temperature radiation detector material today. Although much progress has been made over the past three decades, today's CZT crystals still face certain challenges, especially the presence of the performance-limiting materials defects and the associated relatively high production cost. In this regard, CdxZn1−xTeySe1−y (CZTS) is emerging as a next-generation compound semiconductor, which overcomes some of the limitations of CZT technology for the stated applications. Here, we conducted a study to evaluate the crystalline quality of the traveling heater method grown CZTS with an optimized alloy composition, i.e., Cd0.9Zn0.1Te0.98Se0.02. The as-grown samples were evaluated by low-temperature photoluminescence (PL) spectroscopy and high-resolution x-ray diffraction using the synchrotron light source at Brookhaven National Laboratory. The full width at half maximum of both the PL and x-ray rocking curves was observed to be broadened due to the lattice disorder of the quaternary compound, eventually degrading the crystalline quality. This was consistent with density functional theory calculations. [ABSTRACT FROM AUTHOR]

In this research, we studied point defects induced in Bridgman-grown CdZnTe detectors doped with Indium (In), Aluminium (Al), Nickel (Ni), and Tin (Sn). Point defects associated with different dopants were observed, and these defects were analyzed in detail for their contributions to electron/ hole (e/h) trapping. We also explored the correlations between the nature and abundance of the point defects with their influence on the resistivity, electron mobility-lifetime (lμτe) product, and electron trapping time. We used current-deep level transient spectroscopy to determine the energy, capture cross-section, and concentration of each trap. Furthermore, we used the data to determine the trapping and de-trapping times for the charge carriers. In In-doped CdZnTe detectors, uncompensated Cd vacancies (VCd-) were identified as a dominant trap. The VCd- were almost compensated in detectors doped with Al, Ni, and Sn, in addition to co-doping with In. Dominant traps related to the dopant were found at Ev + 0.36 eV and Ev + 1.1 eV, Ec + 76 meV and Ev + 0.61 eV, Ev + 36 meV and Ev + 0.86 eV, Ev + 0.52 eV and Ec 0.83 eV in CZT:In, CZT:InþAl, CZT:InþNi, and CZT:InþSn, respectively. Results indicate that the addition of other dopants with In affects the type, nature, concentration (Nt), and capture cross-section (σ) and hence trapping (tt) and de-trapping (tdt) times. The dopant-induced traps, their corresponding concentrations, and charge capture cross-section play an important role in the performance of radiation detectors, especially for devices that rely solely on electron transport. [ABSTRACT FROM AUTHOR]

In this research, we assessed the abundance of point defects and their influence on the resistivity, the electron mobility-lifetime (μτe) product, and the electron trapping time in CdTeSe crystals grown under different conditions using the traveling heater method. We used current-deep level transient spectroscopy to determine the traps' energy, their capture cross-section, and their concentration. Further, we used these data to determine the trapping and de-trapping times for the charge carriers. The data show that detectors with a lower concentration of In-dopant have a higher density of A-centers and Cd double vacancies (VCd--). The high concentrations of VCd-- and A-centers, along with the deep trap at 0.86 eV and low density of 1.1 eV energy traps, are the major cause of the detectors' low resistivity, and most probably, a major contributor to the low μτe product. Our results indicate that the energy levels of point defects in the bandgap, their concentrations, capture cross-sections, and their trapping and de-trapping times play an important role in the detector's performance, especially for devices that rely solely on electron transport. [ABSTRACT FROM AUTHOR]

We have studied the effect of annealing (at temperatures 300, 400, and 500 °C) on nanoparticulate CdS film on silicon substrate deposited by hybrid Langmuir–Blodgett chemical bath deposition technique. Width, intensity, and the line shape of the longitudinal optical phonon in Raman spectra and photoluminescence (PL) spectra suggest that the annealing brings about coalescence of nanoparticles at 300 °C, increasing the size of the nanoparticles and also increases the red region PL related to surface states. Annealing at 400 °C leads to two different coexistent states, showing larger nanoparticles and bulklike film. On further annealing at 500 °C, PL shows a drastic redshift to PL of bulklike CdS. This is well brought out by resonance Raman measurements and later confirmed by scanning electron microscope data. Most interesting observation is that PL and Raman results together are indicative of phase transformation of nanoparticulate hexagonal CdS film to bulklike cubic CdS film on annealing at 500 °C, unlike cubic to hexagonal structural phase transition observed in bulk CdS films. [ABSTRACT FROM AUTHOR]

We report on the magnetic properties of epitaxial La0.7Ba0.3MnO3 and La0.7Sr0.3MnO3 films on Si (100) and Si (111) substrates using SrTiO3 template layer, which demonstrate magnetic and electrical properties at and above room temperature. The magnetization data show magnetic transition and magnetic hysteresis at and above room room temperature. The films show well-defined magnetic domains. The ferromagnetic resonance studies show anisotropic effects related to ferromagnetic properties of films. The smaller grain size of about 20 nm in manganite films on SrTiO3/Si may be one of the reasons to minimize the strain effect through strain relaxation at the interface between SrTiO3 and manganites through the formation of three-dimensonal islands. [ABSTRACT FROM AUTHOR]

AgGaSe2 crystals grown by the horizontal Bridgman technique were studied by room-temperature micro-Raman scattering and low-temperature photoluminescence (PL) spectroscopies. The most intense Raman line observed had the frequency of 177 cm-1, corresponding to the Γ1(W1) mode. The measurements were performed along the direction of growth of the boule and the line frequency was found to be almost constant within the experimental accuracy. The average full width at half maximum of the Γ1(W1) mode was found to be 4.6 cm-1 and its insignificant variation along the ingot suggests its structural and compositional uniformities. At low temperature (8 K), the main PL peak at 1.772 eV is due to donor-acceptor-pair recombination. A doublet in the excitonic peak, observed at that temperature, suggests a reduced inhomogeneous broadening and the better crystallinity of the sample, when compared with the previous literature. The dispersion of the various PL peaks along the length of the ingot was also found negligible, which indicates the compositional homogeneity and the uniform distribution of the intrinsic defects. [ABSTRACT FROM AUTHOR]

AgGaSe2 crystals grown by the horizontal Bridgman technique were studied by room-temperature micro-Raman scattering and low-temperature photoluminescence (PL) spectroscopies. The most intense Raman line observed had the frequency of 177 cm-1, corresponding to the Γ1(W1) mode. The measurements were performed along the direction of growth of the boule and the line frequency was found to be almost constant within the experimental accuracy. The average full width at half maximum of the Γ1(W1) mode was found to be 4.6 cm-1 and its insignificant variation along the ingot suggests its structural and compositional uniformities. At low temperature (8 K), the main PL peak at 1.772 eV is due to donor-acceptor-pair recombination. A doublet in the excitonic peak, observed at that temperature, suggests a reduced inhomogeneous broadening and the better crystallinity of the sample, when compared with the previous literature. The dispersion of the various PL peaks along the length of the ingot was also found negligible, which indicates the compositional homogeneity and the uniform distribution of the intrinsic defects. [ABSTRACT FROM AUTHOR]

We have reported the structural, thermal, microscopic, magnetization, polarization, and dielectric properties of BiFeO3 ceramics synthesized by a rapid liquid-phase sintering technique. Optimum conditions for the synthesis of single-phase BiFeO3 ceramics were obtained. Temperature-dependent magnetization and hysteresis loops indicate antiferromagnetic behavior in BiFeO3 at room temperature. Although saturated ferroelectric hysteresis loops were observed in single-phase BiFeO3 ceramic synthesized at 880 °C, the reduced polarization is found to be due to the high loss and low dielectric permittivity of the ceramic, which is caused by higher leakage current. [ABSTRACT FROM AUTHOR]

We report on the fabrication of highly epitaxial Y2O3:Eu3+ and Lu2O3:Eu3+ films on sapphire and Si single crystalline, and quartz substrates under different growth and optimization conditions using pulsed-laser deposition technique. The films were characterized using x rays, microstructure, and spectroscopic measurements. Our results demonstrate superior spectroscopic performance on the films grown on sapphire substrates due to the high quality and epitaxial nature of the film. The surface morphology of the epitaxial films controls the photoluminescence property of these phosphors film. [ABSTRACT FROM AUTHOR]

In this article, we report on the charge-transport characteristics of a new quaternary material Cd1-xZnxTe1-ySey (CZTS) grown by the Traveling Heater Method (THM). The as-grown CZTS material was found to possess fewer Te inclusions than CZT†. Moreover, high resistivity of ∼1-2x1010 ohm-cm was achieved, meeting the requirements of most gamma-ray detector applications. The mobility-lifetime product for electrons [(μτ)e] was measured to be ∼4x10-3 cm2/V. The energy resolution for the quasi-hemispherical detector fabricated from the as-grown CZTS ingot obtained was ∼2.8% (FWHM) at 662 keV. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the role of silicon and oxygen impurities in gallium antimonide grain boundary. Analysis of the electrical properties of adjacent grain of n-type and p-type samples; Discussion on the effect of hydrogen annealing on segregated impurities and barrier height; Factor which causes the barrier height.