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The transmission and reflection spectra of a CdSiP2 single crystal are measured in the temperature interval from 80 to 300 K using the terahertz (THz) pulsed and infrared Fourier spectroscopy methods. A significant influence of postgrowth defects on the absorption in the THz frequency range is revealed. This absorption is found to depend weakly on temperature compared to that observed previously for other chalcopyrite crystal with substantially lower concentration of defects. Upon cooling, intrinsic absorption mechanisms are minimized, and the contribution of defects to absorption is separated. [ABSTRACT FROM AUTHOR]

The temperature and polarization behaviors of four absorption bands in p-type CdGeAs2 bulk crystals have been studied from 5 to 300 K. One band, peaking near 0.22 eV (5.5 μm), is the V2→V1 intervalence band transition, and its intensity taken with E∥c is about 2.8 times larger than that taken with E⊥c. Three additional absorption bands can be separately resolved below 200 K. A broad band peaking near 0.38 eV is present only with E∥c. A second broad band peaking near 0.52 eV is detected using E⊥c. These two bands are assigned to transitions from the top two valence bands to a deep acceptor. Infrared photoluminescence studies of a 0.35 eV emission confirm the presence of the deep acceptor. A third absorption band peaking near 0.56 eV is detected using E∥c. This band is assigned to transitions from a shallow 120 meV acceptor to shallow donor states and/or conduction band states. At room temperature, the normally observed broad absorption feature extending from the band edge to beyond 0.2 eV is a result of the superposition of the four bands. These absorption bands presently limit the use of p-type CdGeAs2 crystals as nonlinear optical materials in infrared high-power laser systems. [ABSTRACT FROM AUTHOR]

A photoluminescence (PL) study has been performed from 5 to 200 K on a series of p-type bulk CdGeAs2 single crystals. Within our large set of samples, the peak position of an emission band at 5 K was observed to vary from about 0.54 to 0.58 eV when using 1064 nm excitation with a power density of 2.5 W/cm2. The variations of the PL peak position with excitation power and sample temperature have been measured and are consistent with donor-acceptor pair (DAP) recombination in the presence of potential fluctuations. We find that the position of the DAP emission in a particular crystal depends on the hole carrier concentration and the level of compensation. Thermal quenching activation energies of 14 and 120 meV are determined for the donor and acceptor states, respectively. The acceptor defect involved in this radiative recombination is the primary center responsible for the commonly observed room-temperature absorption band at 5.5 μm in p-type CdGeAs2 crystals. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) has been used to investigate chromium ions in single crystals of CdGeAs[sub 2] grown by the horizontal gradient freeze technique. Signals from Cr[sup 2+] and Cr[sup 4+] ions were observed near 12 K. The Cr[sup 2+] ions have the 3d[sup 4] configuration with S=2 and substitute at the cadmium sites, while the Cr[sup 4+] ions have the 3d[sup 2] configuration with S=1 and substitute at the germanium sites. As a result, each impurity represents a neutral center. Both EPR spectra display the tetragonal symmetry of the lattice, which suggests that the centers most likely are not perturbed by nearby defects. The ratio of Cr[sup 2+] ions to Cr[sup 4+] ions in a particular CdGeAs[sub 2] crystal depends on the growth conditions and stoichiometry. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An optical absorption investigation from 10 to 296 K has been performed on bulk crystals of ZnGeP[sub 2] grown by the horizontal-gradient-freeze method. We identify three broad absorption bands in the spectral range from 1 to 4 μm that are due to native defects. At low temperature, a band peaking near 1.2 μm and another band peaking near 2.2 μm have intensities that correlate. The strength of these two absorption bands can be increased or decreased by illuminating the crystal with selected laser wavelengths. The 2.2 μm band is strongly polarized, with its greatest intensity occurring when E is parallel to the c axis of the crystal. A third absorption band, peaking near 2.3 μm and extending from 1.5 μm to beyond 4 μm, was observed at low temperature, during and immediately after illumination. Comparison of photoinduced changes in absorption with photoinduced changes in electron paramagnetic resonance spectra allowed specific defects to be associated with each of the three absorption bands. Both the 1.2 and the 2.2 μm bands involve the singly ionized zinc vacancy. The third band at 2.3 μm involves neutral phosphorus vacancies. Specific models for the optical transitions are discussed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]