INVESTIGATION OF POSSIBILITY OF THE MISFIT DISLOCATION DENSITY REDUCTION IN GE / SI FILMS WITH A BUFFER LAYER

В работе исследована возможность улучшения качества гетероэпитаксиальных структур Ge / Si с буферным слоем. Показано, что при использовании подготовительного слоя, состоящего из наноостровков, зарощенных низкотемпературным буферным слоем, возможно проявление так называемого эффекта аннигиляции дислокаций несоответствия в объеме буферного слоя Buf, что значительно улучшает приборное качество получаемых структур. Представлена зависимость морфологии поверхности слоя чистого Ge на буфере от времени роста наноостровков в интерфейсе Si / Buf . Выявлены оптимальные технологические параметры роста наноостровков для получения слоя Ge с минимальной значением шероховатости. Наилучших результатов удалось достичь при времени осаждения наноостровков 2 мин. При этом была достигнута минимальное значение шероховатости поверхности, равное 78 нм. Показано, что при дальнейшем увеличении размеров наноостровков, процесс аннигиляции дефектов замедляется, и рост низкотемпературного буферного слоя сменяется трехмерным островковым ростом, что увеличивает перепады рельефа поверхности выращиваемого слоя. The possibility of improving the quality of Ge / Si heteroepitaxial structures with a buffer layer is investigated. It is shown that when using a preparatory layer consisting of nanostructures overgrown with a low-temperature buffer layer, it is possible to manifest the so-called effect of annihilation of the misfit dislocations in the bulk of the buffer layer Buf , which significantly improves the quality of the resulting structures. The dependence of the morphology of the surface of the pure Ge layer on the buffer on the growth time of nanostructures in the Si / Buf interface is presented. The optimal technological parameters of the growth of nanostructures for obtaining a Ge layer with a minimum roughness value are revealed. The best results were achieved when the deposition time of nanostructures was 2 min. At the same time, the minimum surface roughness value of 78 nm was achieved. It is shown that with a further increase in the size of the nanostructures, the process of annihilation of defects slows down, and the growth of the low-temperature buffer layer is replaced by a three-dimensional island growth, which increases the differences in the relief of the surface of the grown layer.

Atomic-Scale Insights on Large-Misfit Heterointerfaces in LSMO/MgO/c-Al2O3

Understanding the interfaces in heterostructures at an atomic scale is crucial in enabling the possibility to manipulate underlying functional properties in correlated materials. This work presents a detailed study on the atomic structures of heterogeneous interfaces in La0.7Sr0.3MnO3 (LSMO) film grown epitaxially on c-Al2O3 (0001) with a buffer layer of MgO. Using aberration-corrected scanning transmission electron microscopy, we detected nucleation of periodic misfit dislocations at the interfaces of the large misfit systems of LSMO/MgO and MgO/c-Al2O3 following the domain matching epitaxy paradigm. It was experimentally observed that the dislocations terminate with 4/5 lattice planes at the LSMO/MgO interface and with 12/13 lattice planes at the MgO/c-Al2O3 interface. This is consistent with theoretical predictions. Using the atomic-resolution image data analysis approach to generate atomic bond length maps, we investigated the atomic displacement in the LSMO/MgO and MgO/c-Al2O3 systems. Minimal presence of residual strain was shown at the respective interface due to strain relaxation following misfit dislocation formation. Further, based on electron energy-loss spectroscopy analysis, we confirmed an interfacial interdiffusion within two monolayers at both LSMO/MgO and MgO/c-Al2O3 interfaces. In essence, misfit dislocation configurations of the LSMO/MgO/c-Al2O3 system have been thoroughly investigated to understand atomic-scale insights on atomic structure and interfacial chemistry in these large misfit systems.

In-Depth Experimental Analysis of Influence of Electroplated Gold Thickness on Thermal and Electro-Optical Properties of mid-IR AlInAs/InGaAs/InP Quantum Cascade Lasers

In this paper, we have examined the influence of electroplated gold thickness on the thermal and electro-optical properties of mid-IR AlInAs/InGaAs, InP QCLs. The experimental results show a significant reduction of the temperature of QCL active region (AR) with increasing gold layer thickness. For QCLs with 5.0 μm gold thickness, we observed a 50% reduction of the active region temperature. An improvement of key electro-optical parameters, that is, threshold current density and maximum emitted power for structures with thick gold, was observed. The results of micro-Raman characterization show that the electroplated gold layer introduces only moderate compressive strain in top InP cladding, which is well below the critical value for the creation of misfit dislocations.

A Review of the Reliability of Integrated IR Laser Diodes for Silicon Photonics

With this review paper we provide an overview of the main degradation mechanisms that limit the long-term reliability of IR semiconductor lasers for silicon photonics applications. The discussion is focused on two types of laser diodes: heterogeneous III–V lasers bonded onto silicon-on-insulator wafers, and InAs quantum-dot lasers epitaxially grown on silicon. A comprehensive analysis of the reliability-oriented literature published to date reveals that state-of-the-art heterogeneous laser sources share with conventional laser diodes their major epitaxy-related degradation processes, such as the generation of non-radiative recombination centers or dopant diffusion, while eliminating cleaved facets and exposed mirrors. The lifetime of InAs quantum dot lasers grown on silicon, whose development represents a fundamental step toward a fully epitaxial integration of future photonic integrated circuits, is strongly limited by the density of extended defects, mainly misfit dislocations, protruding into the active layer of the devices. The concentration of such defects, along with inefficient carrier injection and excessive carrier overflow rates, promote recombination-enhanced degradation mechanisms that reduce the long-term reliability of these sources. The impact of these misfits can be largely eliminated with the inclusion of blocking layers.

Impact of Long-Term Annealing on Photoluminescence from Ge1−xSnx Alloys

We report on the connection between strain, composition, defect density and the photoluminescence observed before and after annealing at 300 °C for GeSn samples with Sn content of 8% to 10%. Results show how the composition and level of strain influenced the separation between the indirect and direct optical transitions, while changes in the level of strain also influenced the density of misfit dislocations and surface roughness. The effect of annealing is observed to lower the level of strain, decreasing the energy separation between the indirect and direct optical transitions, while also simultaneously increasing the density of misfit/threading dislocations and surface roughness. The reduction in energy separation leads to an increase of photoluminescence (PL) emission, while the increase of misfit/threading dislocations density and surface roughness results in a decrease of PL. Consequently, the competition between these factors is observed to determine the impact of annealing on the PL. As a result, annealing increases the collected PL for small (≤40 meV) separation between the indirect to direct optical transitions in the as-grown sample while decreases the PL for larger (≥60 meV) separations. More generally, these numbers have a small dependence on the level of strain in the as-grown samples.