N. V. Sochinskii

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 500–600u2009u2009°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 340u2009°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.

Effect of α-HgI2 epitaxial growth on the defect structure of CdTe:Ge substrates

The α-HgI2/CdTe:Ge heterostructures have been studied by cathodoluminescence (CL) in the scanning electron microscope. The α-HgI2 expitaxial growth was shown to cause an enhancement of the CL intensity in a layer of the substrate extending up to about 500 μm from the α-HgI2/CdTe:Ge interface. CL spectra of the layer reveal the appearance of a band related to tellurium vacancies as well as the decrease of the emission attributed to defect complexes involving Ge. The data obtained indicate that Ge-impurity gettering and VTe generation at the interface take place during α-HgI2 epitaxial growth.

Hg1−xCdxI2/CdTe heterostructures for nuclear radiation detectors: Effect of epitaxial growth on substrate properties

We demonstrate the possibility to fabricate nuclear radiation detectors operating at room temperature from CdTe substrates affected by the vapor phase epitaxy (VPE) growth of Hg1−xCdxI2 layers. The VPE layers with the thickness 10–30 μm were grown using an α-HgI2 polycrystalline source at 220u2009°C and time in the range of 30–100 h. The as-grown heterostructures were chemically etched to remove the epilayers, and Au–CdTe–Au detectors were made. The substrates were characterized by synchrotron x-ray topography before and after the VPE growth, and the current–voltage (I–V) and spectroscopic measurements of the detectors were carried out. The effect of the VPE growth on the substrates and detectors has been studied and on the basis of this it has been possible to fabricate γ-ray detectors with Ohmic I–V characteristic and good spectral response.

Low-pressure synthesis and Bridgman growth of Hg1−xMnxTe

To reduce Hg high pressure related to the high-temperature synthesis reaction between the components in elemental form, Hg 1-x Mn x Te bulk crystals were produced by a two-step procedure including (I) the alloy synthesis using HgTe crystals grown by the cold travelling heater method and elemental Mn and Te to complete the desired composition, followed by (II) the Bridgman growth. The growth was carried out at temperature in the range of 700-850°C and rate of 1 mm/h. The Hg 1-x Mn x Te crystals have been characterised by X-ray diffractometry, energy dispersive X-ray analysis, Fourier transformed infrared spectroscopy and Hall effect techniques. Although the distribution coefficient of Mn was found to be in the range of 3-3.5 in the first-to-freeze region, the crystals show a good axial composition uniformity throughout more than a half of the total length. The lattice parameter of Hg 1-x Mn x Te is reported for the studied composition range x = 0-0.15.

Structural properties of CdTe and Hg1 − xCdxTe epitaxial layers grown on sapphire substrates

Abstract Structural properties of CdTe and Hg 1 − x Cd x Te epitaxial layers have been investigated by X-ray topography, high resolution X-ray diffractometry and Rutherford backscattering spectrometry. CdTe 5–10 μm thick layers were grown on commercial sapphire (0001) substrates by metalorganic vapour phase epitaxy (MOVPE) at 340°C for 1–3.5 h using dimethyl-cadmium and diisopropyl-tellurium as precursors. Hg 1 − x Cd x Te 15–30 μm thick layers with an uniform composition x = 0.2 or 0.3 were obtained at 530–550°C for 70–120 h by vapour phase epitaxy (VPE) of HgTe on CdTe MOVPE layers which was followed by interdiffusion of Hg and Cd. Despite the strain originated by a big lattice mismatch at the layer/substrate interface, it was shown that the combination of X-ray and RBS/channelling characterization techniques provides the information on crystalline quality, composition and orientation throughout the thickness and area of the CdTe MOVPE and Hg 1 − x Cd x Te VPE layers. Our results are useful for the future progress in selective area epitaxy of CdTe and Hg 1 − x Cd x Te.

Laser-assisted recrystallization to improve the surface morphology of CdTe epitaxial layers

Laser-assisted recrystallization has been studied in order to improve the surface morphology of CdTe layers grown on sapphire substrates by metalorganic vapour phase epitaxy (MOVPE). The recrystallization was carried out by scanning the surface of as-grown CdTe MOVPE layers with an Ar ion laser beam ( = 514.5 nm) as the laser power varied in the 140 - 600 mW range. The irradiation time was in the range from 10 s to 5 min. The effect of the recrystallization layers surface procedure on the structure has been investigated by scanning electron microscopy, Rutherford backscattering spectrometry and spectroscopic ellipsometry. Depending on the laser power and irradiation time, the recrystallization was shown to occur either within the entire layer thickness or on the layer surface. Due to recrystallization, the surface microrelief of the layers has been improved all over the recrystallized area and the surface roughness has been uniformly decreased from 1.5 m to 0.2 m. The data obtained show that it might be possible to engineer CdTe MOVPE layers using post-growth laser-assisted recrystallization, making them more suitable for infrared applications.

Cathodoluminescence study of laser recrystallized CdTe layers

CdTe(100)/GaAs(100) and CdTe(lll)/CdTe(lll) layers grown by metalorganic vapor phase epitaxy (MOVPE) were investigated The layers were recrystallized to improve their morphology by scanning the surface with a 100 mu m diameter spot from an Ar ion laser beam (lambda=514.4 nm). Cathodoluminescence spectra from both as-grown and recrystallized CdTe MOVPE layers are used to monitor the effect of the recrystallization procedure. The laser recrystallization results in important changes on the spectral distribution of luminescence. Deep-level bands associated to different defects are shown to be very sensitive to the laser recrystallization procedure. The effect of the different substrates on the defect structure of the layers is also related to the changes observed in the cathodoluminescence spectra.

Vapor phase epitaxy of Hg1−xCdxI2 layers on CdTe substrates

Vapor phase epitaxy (VPE) has been studied to grow Hg1 − xCdxI2 epitaxial layers on CdTe bulk substrates. The effect of the VPE growth conditions on the morphology, composition and crystalline quality of Hg1 − xCdxI2CdTe heterostructures has been investigated. It has been shown that 10–30 μm thick Hg1 − xCdxI2 layers can be successfully grown using an α-HgI2 polycrystalline source under isothermal conditions at a temperature in the range 170–240°C for the time period 20–50 h. Interestingly, the VPE growth was found to consist of two successiv stages with different kinetics as follows: (1) a fast growth of an HgI2 platelet layer on the CdTe substrate surface and (2) a slow growth of an Hg1 − xCdxI2 layer on the surface of the platelet layer. The Hg1 − xCdxI2 layers exhibited single-crystalline structure when the layer composition has been varied in the wide range x = 0.24−0.67. The particular role of the HgI2 platelet layer morphology in controlling the composition uniformity throughout the thickness of the Hg1 − xCdxI2 layer has been demonstrated.