V. P. Martovitsky

Ge/GeSn heterostructures grown on Si (100) by molecular-beam epitaxy

The growth of GeSn layers by molecular-beam epitaxy on Si (100) wafers coated with a germanium buffer layer is investigated. The properties of the fabricated structures are controlled by reflection high-energy electron diffraction, atomic-force microscopy, X-ray diffractometry, Rutherford backscattering, and Raman scattering. It is shown that GeSn layers with thicknesses up to 0.5 μm and Sn molar fractions up to 0.073 manifest no sign of plastic relaxation upon epitaxy. The lattice constant of the GeSn layers within the growth plane is precisely the same as that of Ge. The effect of rapid thermal annealing on the conversion of metastable elastically strained GeSn layers into a plastically relaxed state is examined. Ge/GeSn quantum wells with Sn molar fraction up to 0.11 are obtained.

Silicon-germanium nanostructures with high germanium concentration

The impact of nucleation conditions on the quality of epitaxial layers of germanium and GeSi alloys containing a high Ge mole fraction grown on (100) silicon substrates using electron-beam epitaxy is considered. The GexS1-x/Ge superlattices are grown on a GeySi1-y (x > y) relaxed buffer layer. X-ray diffractometry, atomic force microscopy and Auger spectroscopy are the main techniques used to study the properties of the grown structures.

On the structure of the superconducting order parameter in high-temperature Fe-based superconductors

1 P.N. Lebedev Physical Institute RAS, 119991 Moscow, Russia 2 M.V. Lomonosov Moscow State University, 119991 Moscow, Russia 3 National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 115409 Moscow, Russia 4 International Laboratory of High Magnetic Fields and Low Temperatures, 53-412 Wroclaw, Poland 5 National University “Higher School of Economics”, 101000 Moscow, Russia

MBE GROWN ZnSSe/ZnMgSSe MQW STRUCTURE FOR BLUE VCSEL

ZnSSe/ZnMgSSe MQW structures were grown by molecular beam epitaxy on GaAs substrates. The band gap of ZnMgSSe barriers was approximately 3 eV at room temperature. Cathodoluminescence, X-ray diffraction, optical, scanning electron beam, and atomic force microscopy were all used for structure characterization. Decay of the ZnMgSSe solid solution in at least two phases was observed. Improvement in the quality of the crystal lattice and surface morphology was achieved by mismatching the ZnMgSSe from the GaAs substrate by increasing the lattice period by 0.24%.

Molecular Beam Epitaxy of Si–Ge–Sn Heterostructures for Monolithically Integrated Optoelectronic Devices Based on Silicon

Elastically strained metastable Ge1–xSnx layers with molar fractions of tin of up to 0.15 are grown on Si (001) substrates. To analyze the optical properties of the samples, photoluminescence (PL) spectra are measured at room temperature and IR transmission spectra are measured at the liquid helium temperature. The room temperature direct intrinsic absorption edge at 0.71–0.72 eV is visible in the spectra of the studied structures with tin contents of 12–13%.

Sn-enriched Ge/GeSn nanostructures grown by MBE on (001) GaAs and Si wafers

Elastically stressed metastable GeSn layers with a tin molar fraction as large as 0.185 are grown on (001) Si and GaAs wafers covered with a germanium buffer layer. A set of wafers with a deviation angle in the range 0°–10° is used. It is established that the GeSn crystal undergoes monoclinic deformation with the angle β to 88° in addition to tetragonal deformation. Misorientation of the wafers surface results in increasing efficiency of the incorporation of tin adatoms into the GeSn crystal lattice. Phase separation in the solid solution upon postgrowth annealing of the structures begins long before the termination of plastic relaxation of elastic heteroepitaxial stresses. Tin released as a result of GeSn decomposition predominantly tends to be found on the surface of the sample. Manifestations of the brittle–plastic mechanism of the relaxation of stresses resulting in the occurrence of microcracks in the subsurface region of the structures under investigation are found.

Layer structure of Zn1−xCdxSe films grown by vapor-phase epitaxy from metal-organic compounds on Cd0.92Zn0.08S(0001) substrates

The structure of Zn1−xCdxSe films, which were grown by vapor-phase epitaxy from metal-organic compounds on a Cd0.92Zn0.08S(0001) substrate, was investigated by X-ray diffractometry. For both cubic and hexagonal phases, asymmetric reflections were selected. These reflections make it possible not only to reliably determine the presence of these phases in the film, but also to estimate the dimensions of coherent X-ray scattering regions and (or) variation in the lattice parameters in the intergrowth plane. The ZnSe films preferentially consist of twinned interlayers of the cubic phase, 200–250 Å thick, and with a low content of the hexagonal phase. In contrast, the hexagonal phase with a small number of cubic interlayers predominates in CdSe films. The thickness of the interlayers of the cubic phase in Zn1−xCdxSe decreases, whereas the concentration of the hexagonal phase increases for low x values with an approximately identical development of both phases for x=0.15–0.20.

MBE Growth of II–VI Epilayers and QW Structures on Hexagonal ZnCdS and CdSSe Substrates

ZnTe, ZnSe layers and ZnCdTe/ZnTe, ZnCdSe/ZnSe quantum well structures were grown on hexagonal Zn 0.05 Cd 0.95 S(0001) and CdS 0.85 Se 0.15 (1120) by molecular beam epitaxy and studied by cathodoluminescence (CL), photoreflection, and X-ray diffraction. The structures grown on the (1120) substrates had rough surface while the structures grown on the (0001) substrate were mirror-like. All structures were cubic. In the ZnSe based structures, the (111) and (110) lattice directions of epilayers coincided with the (0001) and (1120) directions of CdZnS(0001) substrate, respectively. High mismatching leaded to a lattice relaxation of these epilayers by introduction of misfit dislocations. This was the reason of low CL intensity. In spite of higher mismatching, the ZnTe based epilayers grown on (0001) substrates had more perfect lattice structure and more intense CL than ZnSe based epilayers. Cubic lattice of ZnTe was found to be rotated approximately by 15° around the (111) direction coincided with the (0001) direction of the (0001) substrate. It was proposed that a geometrical lattice matching took place at epitaxy of ZnTe on the CdZnS(0001).

Investigation of the thermal stability of metastable GeSn epitaxial layers

A stack of five elastically strained metastable GeSn layers with a thickness of 200 nm each separated by Ge spacer layers with a thickness of 20 nm is grown on a (001) Si/Ge virtual substrate. The molar fraction of Sn in the GeSn layers is 0.005, 0.034, 0.047, 0.072, and 0.10. After growth the structure is subjected to thermal annealing for 2 min at a temperature of 400°C. It is demonstrated that during the course of annealing the GeSn alloy, along with plastic relaxation, undergoes phase separation; this phase separation begins before the end of plastic relaxation. The structural degradation of the GeSn layers increases with increasing concentration of Sn accumulated on the structure surface in the form of an amorphous layer.