E. Diéguez

Nature of compensating luminescence centers in Te-diffused and -doped GaSb

Diffusion of tellurium in undoped p‐GaSb has been carried out. Using the cathodoluminescence and photoluminescence techniques, the luminescence centers in Te‐diffused samples have been identified and compared with the Te‐doped bulk GaSb. Fundamental differences in the radiative levels are observed between the diffused and the as‐grown doped samples. Evidence for self‐compensating acceptor complexes are seen in diffused samples. With short and moderate diffusion times, a compensating acceptor complex VGaGaSbTeSb is observed. For long diffusion times, the dominant acceptor center has been attributed to the antisite defect GaSb or related complex. The reasons for the formation of various acceptor centers have been discussed.

Changes in the solid-liquid interface during the growth of Bi12SiO20, Bi12GeO20 and LiNbO3 crystals grown by the Czochralski method

Solid-liquid interfaces during automated Czochralski crystal growth are systematically studied for different oxide materials. The shape of the core in Bi12SiO20 and Bi12GeO20 is related to the interface curvature. Numerical calculations are performed in order to obtain temperature profiles and flow patterns for different melt heights. The experimental results widely confirm the theoretically predicted interface shapes at different stages of the growth process.

Flat interface in the growth of LiNbO3, Bi12SiO20 and Bi12GeO20 crystals from the melt

Abstract The influence of crystal rotation rate and axial temperature gradient was investigated in the growth of high quality LiNbO 3 , Bi 12 GeO 20 and Bi 12 SiO 20 crystals. The meniscus weight in the withdrawal of the crystals was used as a tool to know the shape of the interface. This interface shape was simulated for different values of the rotation rate at a constant axial temperature gradient, and compared successfully with the experimental interface shape. The optimal experimental conditions to obtain a flat interface are discussed.

Optical properties of Dy3+ doped yttrium–aluminium borate

A Dy3+ doped yttrium–aluminium borate (Dy:YAB) crystal has been optically characterized. The refractive indices at seven different wavelengths, ranging from the visible to the near infrared (IR), have been measured and the Sellmeier curves have been calculated. The polarized optical absorption spectra have been obtained at room temperature, and the Judd–Ofelt parameters have been calculated. The lifetime of the upper laser level 4F9/2 has been estimated and compared with the experimental value. Evidence of high luminescence quantum efficiency of the 4F9/2 state in YAB is provided by measured lifetimes.

Self-frequency doubling in Yb3+ doped periodically poled LiNbO3:MgO bulk crystal

Continuous-wave laser action from an Yb3+ doped periodically poled LiNbO3:MgO bulk crystal at 1.06 μm is reported. In addition, efficient and stable self-frequency-doubled laser action at 531 nm was obtained by quasiphase matching. Up to 10.5 mW of green output power is obtained from a total laser output power of 58 mW. The experiments were carried out by end pumping with a Ti:sapphire laser, as a surrogate source for a diode laser, at 980 nm. Laser operation was stable at room temperature. The results are compared with those corresponding to single-domain Yb-doped crystals.

Effect of thermal annealing on Te precipitates in CdTe wafers studied by Raman scattering and cathodoluminescence

A combination of Raman scattering and cathodoluminescence techniques has been used to study the spatial distribution of Te precipitates in the volume of CdTe wafers. Starting with the as‐grown crystals with random distribution of precipitates over the whole volume, improvement at different stages of thermal annealing is demonstrated. As‐grown p‐CdTe wafers were annealed at 500–600  °C either in Ga melt or in Cd vapor for 2 or 22 h. The kinetics of dissolution of Te precipitates was found to be similar for both the Ga melt and Cd vapor annealing processes. Short‐time annealing causes the disappearance of small Te precipitates, while the larger ones, 5–10 μm in size which decorate the extended structural defects, still remain. After a long‐time annealing, the complete disappearance of Te precipitates occurs in the wafers volume. Interestingly, it was observed that the disappearance of Te precipitates during annealing starts in the central part of the bulk wafer and is followed by a precipitate gettering at ...

SUBSTRATE EFFECT ON CDTE LAYERS GROWN BY METALORGANIC VAPOR PHASE EPITAXY

CdTe layers were grown by metalorganic vapor phase epitaxy (MOVPE) on different substrates like sapphire, GaAs, and CdTe wafers. The growth was carried out at the temperature 340 °C and time in the range of 2–4 h using dimethyl-cadmium and diisopropil-tellurium as precursors. The layers were studied by scanning electron microscopy, Rutherford backscattering spectroscopy, and high resolution low-temperature photoluminescence spectroscopy. The surface morphology and RBS and PL spectra of CdTe MOVPE layers are reported and the substrate effect on the layer properties is demonstrated.

Cathodoluminescence characterization of Ge‐doped CdTe crystals

Cathodoluminescence (CL) microscopic techniques have been used to study the spatial distribution of structural defects and the deep levels in CdTe:Ge bulk crystals. The effect of Ge doping with concentrations of 1017 and 1019 cm−3 on the compensation of VCd in CdTe has been investigated. Dependence of the intensity distribution of CL emission bands on the dopant concentration has been studied. Ge doping causes a substantial reduction of the generally referred to 1.40 eV luminescence, which is often present in undoped CdTe crystals, and enhances the 0.91 and 0.81 eV emissions.

Lattice Site of Iron in LiNbO3(Fe3+) by the PIXE/Channelling Technique

The lattice location of Fe in LiNbO3 single crystals has been investigated by PIXE-channelling techniques. For the first time, it has unambiguously shown that Fe (mostly as Fe3+) lies at or near the Li-site, although a small fraction sitting at the Nb or intrinsic vacant sites cannot be ruled out.

Bulk periodic poled lithium niobate crystals doped with Er and Yb

Periodic poled lithium niobate crystals have been prepared by the Czochralski technique using a non-symmetrical temperature field. Er and Yb ions have been added to the melt in different concentrations and its effect on the formation of the periodical structures has been studied. The periodical domain structures are improved for dopant concentrations lower than the solubility limit. The formation of the periodical domain structures is related with the dopant segregation coefficient value and with the temperature gradient in the interface.