Photoluminescence characteristics of Cd1-xMnxTe single crystals grown by the vertical Bridgman method

In this paper, we report a systematic investigation of band-edge photoluminescence for Cd1-xMnxTe crystals grown by the vertical Bridgman method. The near-band-edge emissions of neutral acceptor-bound excitons (labeled as L1) were systematically investigated as a function of temperature and of alloy composition. The parameters that describe the temperature variation of the energy were evaluated by the semiempirical Varshni relation. From the temperature dependence of the full width at half maximum of the L1 emission line, the broadening factors Γ(T) were determined from the fit to the data. The activation energies of thermal quenching were obtained for the L1 peak from the temperature dependence of the bound exciton peaks and were found to decrease with increasing Mn concentration

Excitation‐Power Dependence of the Near Band‐Edge PL Spectra of CdMnTe with High Mn Concentrations

Temperature and excitation power dependences of photoluminescence (PL) measurements were studied for the CdMnTe crystal grown by the vertical Bridgman method. The near band‐edge and intra‐Mn2+Mn2+ emissions were investigated as a function of temperature. The observed band‐edge peak of the PL spectrum showed a clear blue‐shift with decreasing temperature. However, the peak energy of the intra‐Mn2+Mn2+ transition did not decrease monotonically with changing temperature, as can be seen above 70 K. With increasing the excitation power, the intensity of the emission peak was increased.ope

Optical and electronic properties of highly stable and textured hydrogenated ZnO:Al thin films

We have experimentally investigated the effects of hydrogen-annealing on the structural, electrical, and optical properties of Al-doped ZnO (ZnO:Al) thin films prepared by RF magnetron sputtering at room temperature. From the X-ray diffraction observations, the orientation of ZnO:Al films was found to be a c-axis in the hexagonal structure. We found that intentionally incorporated hydrogen plays an important role in n-type conduction as a donor, improving free carrier concentration and electrical stability. We simultaneously obtained improved optical transmission and enhanced absorption edge of the ZnO:Al film due to hydrogen-annealing. Our experimental data suggest the hydrogen-annealing process as an important role in the enhancement of electrical and optical properties, which is promising as a back reflector material for thin-film solar cells.ope

Impact of Cu substitution on structural, electronic, and optical properties of CdCuTe single crystals

We have experimentally investigated the effects of Cu substitution (0???x???0.03) on structural, electronic, and optical properties of bulk Cd1−xCuxTe, grown by Bridgman method, which is an important semiconductor for photovoltaic applications. A series of X-ray experiments unambiguously demonstrates high-quality Cd1−xCuxTe single crystals oriented along a (110) direction without clusters and/or secondary phases. Ultraviolet photoelectron spectroscopy reveals that the work function of Cd1−xCuxTe is only slightly smaller than that of CdTe. Although the Cu incorporation does not significantly alter the crystal structure, we find that the measured bandgap varies in the range from 1.474 to 1.461 eV at room temperature, which is suitable for photovoltaic applications. Together with the one-photon absorption coefficient, crucial optical parameters describing the temperature dependence of the bandgap are determined based on three analytical models.ope

Electronic and optical properties in ZnO:Ga thin films induced by substrate stress

The effects of biaxial stress in ZnO:Ga thin films on different substrates, e.g., sapphire(0001), quartz, Si(001), and glass have been investigated by X-ray diffraction, atomic force microscopy, and electrical transport and ellipsometric measurements. A strong dependence of orientation, crystallite size, transport, and electronic properties upon the substrate-induced stress has been found. The structural properties indicate that a tensile stress exists in epitaxial ZnO:Ga films grown on sapphire, Si, and quartz, while a compressive stress appears in films grown on glass. The resistivity of the films decreased with increasing biaxial stress, which is inversely proportional to the product of the carrier concentration and Hall mobility. The refractive index n was found to decrease with increasing biaxial stress, while the optical band gap E0 increased with stress. These behaviors are attributed to lattice contraction and the increase in the carrier concentration that is induced by the stress. Our experimental data suggest that the mechanism of substrate-induced stress is important for understanding the properties of ZnO:Ga thin films and for the fabrication of devices which use these materials.ope

Temperature Dependence of the Absorption Edge of Cd1-xMnxTe Crystals

The optical absorption of Cd 1-xMn xTe crystals grown by the Bridgman method was measured as a function of the temperature and the Mn composition x. It was found that the absorption coefficient photon energy depended exponentially, while the energy gap E g depended linearly, on the the Mn composition. With increasing x, the slope parameter ?? and the temperature parameter ?? decreased while the temperature parameter ?? increased. We explained these results in terms of the Mn 2+ ions substituted into the CdTe host material.ope

TEMPERATURE DEPENDENCE OF THE FUNDAMENTAL BAND GAP ENERGY OF Cd1−xCoxTe SINGLE CRYSTALS

Cd1-xCoxTe single crystals were grown by the vertical Bridgman method. The optical band gap energy of Cd1-xCoxTe(x=0,0.001,0.004, 0.008) were obtained as a function of temperature (12 ??? 300K) and cobalt composition x. The temperature variation of the energy gap could be well fitted by the empirical Varshni relation. The temperature coefficient at low temperature decreased with x, but was nearly constant at high temperature. The band gap energy decreased linearly with composition.ope

Structural, Optical, and Magneto-Optical Properties in Diluted Magnetic Semiconductors Cd0.63−yMn0.37CoyTe Single Crystals

We investigated the magneto-optical properties of diluted magnetic semiconductor Cd0.63-yMn0.37CoyTe single crystals grown using a vertical Bridgman method. From the temperature dependence of the band-gap energy, the Varshni temperature parameter alpha was found to increase linearly with increasing Co concentration y while beta decreased with y. The Faraday rotation as a function of photon energy with various Co compositions for CdMnCoTe in the temperature range of 10 to 300 K was measured. The Verdet dispersion curves were enhanced near the fundamental band gap energy. The Verdet constant becomes larger since because the effect of the sp-d exchange interaction is enhanced as the temperature is lowered. At 10 K, the Verdet constants of the Faraday rotation for the samples with y = 0, 0.01, 0.02, and 0.04 were observed to be -0.94, -1.41, -1.69, and -2.11 deg/G cm at 610 nm, respectively. The Verdet constant showed a maximum for the sample with y = 0.04, and the value was approximately 2.3 times larger than that of the Cd0.63Mn0.37Te crystal. The Faraday rotation increased as Co content was increased, and the origin of the enhancement of the Faraday rotation in CdMnCoTe crystals could be explained in terms of the magnetization.ope

Temperature dependence of Vickers hardness for Cd1-xMnxTe (0<x<0.82) single crystals

The Cd1-xMnxTe (0???x???0.82) single crystals were grown by the vertical Bridgman method. The Vickers hardnesses of the grown crystals were measured as a function of Mn composition and temperature for the first time. The activation energy was determined for the dislocation motion from the relation between temperature and hardness, and it was decreased as increasing x in Cd1-xMnxTe single crystals. Also, the Vickers hardness HV was decreased as increasing temperature and increased as Mn composition x.ope

Spectroscopic Ellipsometry Studies of Cd1&#8722;xMnxTe Films Grown on GaAs

Spectroscopic ellipsometry measurements of the complex dielectric function of a series of Cd1-xMnxTe (0 ??? x ??? 0.7) films grown on (100) GaAs by hot wall epitaxy have been performed in the 1.5-5.5 eV photon energy range at room temperature. The measured data were analyzed by fitting the second-derivative spectra (d2??/d??2) with a theoretical model, namely, the standard critical-point (SCP) line shapes. It was found that the SCP model explains the measured derivative spectra successfully. The composition dependence of the critical-point (CP) energies and Lorentzian broadening (??) was determined.ope