Plasma Parameters in the Reactor with Simultaneous Magnetron Discharge and Inductive Radio-Frequency Discharge in the Presence of External Magnetic Field

A plasma reactor that contains vacuum–arc and magnetron sputtering sources and radio-frequency discharge that generates high-density plasma in the presence of external magnetic field is developed, constructed, and optimized. The reactor can be used for deposition of various functional coatings with ion stimulation. The parameters of the inductive radio-frequency discharge generated in the presence of external magnetic field that serves as a source of assisting ions are optimized. It is shown that the working interval of the induction of external magnetic field corresponds to the resonant excitation of the coupled helicon and Trivelpiece–Gold waves. The effect of magnitude and configuration of magnetic field on the parameters of gas-discharge plasma and ion current in the substrate region is studied in the presence of separately and simultaneously initiated magnetron and inductive discharges. The effect of ion flux that is incident on the films in the course of growth on the structure of functional coatings is analyzed.     

Total external x-ray reflection and infrared spectroscopy study of porous silicon and its aging

Study of p-type porous silicon has been carried out by x-ray reflectometry for the first time. Its critical total-external-reflection angle and its reflection coefficient in the subcritical angle range are much smaller than for c-Si, which was grown by the Czochralski method. The critical angle decreases with increase of the porosity. The critical angle and the reflection coefficient increase with aging. These results are attributable to the much smaller electron density of porous silicon in comparison with c-Si, to the microgeometry of its surface, and to changes in both of these factors attendant to aging due to an increase in the concentration of atmospheric constituents observed in the infrared absorption spectra. As the porosity increases, the concentration of atmosmopheric impurities also increases, and in high-porosity material in addition to chemically adsorbed oxygen, carbon and water seem to contribute appreciably. Fiz. Tekh. Poluprovodn. 31, 957–960 (August 1997)     

Layer-by-layer composition and structure of silicon subjected to combined gallium and nitrogen ion implantation for the ion synthesis of gallium nitride

The composition and structure of silicon surface layers subjected to combined gallium and nitrogen ion implantation with subsequent annealing have been studied by the X-ray photoelectron spectroscopy, Rutherford backscattering, electron spin resonance, Raman spectroscopy, and transmission electron microscopy techniques. A slight redistribution of the implanted atoms before annealing and their substantial migration towards the surface during annealing depending on the sequence of implantations are observed. It is found that about 2% of atoms of the implanted layer are replaced with gallium bonded to nitrogen; however, it is impossible to detect the gallium-nitride phase. At the same time, gallium-enriched inclusions containing ～25 at % of gallium are detected as candidates for the further synthesis of gallium-nitride inclusions.     

Influence of the doping type and level on the morphology of porous Si formed by galvanic etching

The formation of porous silicon (por-Si) layers by the galvanic etching of single-crystal Si samples (doped with boron or phosphorus) in an HF/C₂H₅OH/H₂O₂ solution is investigated. The por-Si layers are analyzed by the capillary condensation of nitrogen and scanning electron microscopy (SEM). The dependences of the morphological characteristics of por-Si (pore diameter, specific surface area, pore volume, and thickness of the pore walls), which determine the por-Si combustion kinetics, on the dopant type and initial wafer resistivity are established.     

Formation of carbon nanotubes on an amorphous Ni<Subscript>25</Subscript>Ta<Subscript>58</Subscript>N<Subscript>17</Subscript> alloy film by chemical vapor deposition

It is shown that it is possible to grow carbon nanotubes on the surface of an amorphous Ni–Ta–N metal alloy film with a low Ni content (~25 at %) by chemical deposition from acetylene at temperature 400–800°C. It is established that the addition of nitrogen into the Ni–Ta alloy composition is favorable for the formation of tantalum nitride and the expulsion of Ni clusters, which act as a catalyst of the growth of carbon nanotubes, onto the surface. From Raman spectroscopy studies, it is found that, as the temperature of synthesis is raised, the quality of nanotubes is improved.     

Thermodynamics of the formation of catalyst clusters for carbon nanotube growth

A fundamental thermodynamic model of formation of catalyst clusters for growing carbon nanotubes has been developed and model predictions have been compared with the experimental data. An expression for the size distribution function of clusters, depending on the conditions of their formation, is obtained. It is shown that surface tension plays an important role in the cluster formation. The surface tension coefficient for iron clusters at 950°C is determined.     

Nonalloyed ohmic contacts for high-electron-mobility transistors based on AlGaN/GaN heterostructures

A microwave field-effect transistor with nonalloyed ohmic contacts is fabricated using the technique of regrowing a heavily doped region under the contact metallization by molecular beam epitaxy through a preliminarily formed dielectric mask. The fabricated field-effect transistor with a gate length of 0.18 µm and a total width of 100 µm has a current–amplification cutoff frequency of 66 GHz and ohmic contact resistivity of 0.15-0.18 Ω mm.     

Features of the selective manganese doping of GaAs structures

The effect of technological parameters on the selective manganese doping of arsenide–gallium heterostructures fabricated by a combination of methods of MOS-hydride epitaxy and pulsed-laser deposition is investigated. As these parameters, the impurity content in the manganese δ layer and the structureformation temperature are used. It is established that the prepared structures demonstrate the highest electrical activity and have ferromagnetic properties at a growth temperature of ~400°C and an impurity content of no higher than 0.2–0.3 monolayers. Studying the grown structures by the methods of reflection spectroscopy, high-resolution transmission electron microscopy, and secondary-ion mass spectrometry shows that use of the above conditions in the case of pulsed laser deposition makes it possible to obtain arsenide–gallium structures, which have good crystalline quality, and manganese is concentrated in them within a thin (7–8 nm) layer without substantial diffusion-induced spreading and segregation.     

Laser-Printed Plasmonic Metasurface Supporting Bound States in the Continuum Enhances and Shapes Infrared Spontaneous Emission of Coupled HgTe Quantum Dots

In order to advance the development of quantum emitter-based devices, it is essential to enhance light-matter interactions through coupling between semiconductor quantum dots with high quality factor resonators. Here, efficient tuning of the emission properties of HgTe quantum dots in the infrared spectral region is demonstrated by coupling them to a plasmonic metasurface that supports bound states in the continuum. The plasmonic metasurface, composed of an array of gold nanobumps, is fabricated using single-step direct laser printing, opening up new opportunities for creating exclusive 3D plasmonic nanostructures and advanced photonic devices in the infrared region. A 12-fold enhancement of the photoluminescence in the 900–1700 nm range is observed under optimal coupling conditions. By tuning the geometry of the plasmonic arrays, controllable shaping of the emission spectra is achieved, selectively enhancing specific wavelength ranges across the emission spectrum. The observed enhancement and shaping of the emission are attributed to the Purcell effect, as corroborated by systematic measurements of radiative lifetimes and optical simulations based on the numerical solution of Maxwell's equations. Moreover, coupling of the HgTe photoluminescence to high quality factor modes of the metasurface improves emission directivity, concentrating output within an ≈20° angle.     

Influence of optical losses on the dynamic characteristics of linear arrays of near-infrared vertical-cavity surface-emitting lasers

The effect of the level of internal and external optical losses on the dynamic characteristics of vertical-cavity surface-emitting lasers (VCSELs) in the spectral region of 850 nm is studied. It is shown that an increase in optical losses leads to a decrease in the speed of laser response and to the predominance of thermal effects, while a decrease in losses for the output of radiation brings about an increase in the response speed of the laser and the dominance of damping of the effective modulation frequency. Linear matrix emitters with the 1 × 4 format based on fast-response VCSEL with individual element addressing are produced and studied. Individual laser emitters with a current-aperture diameter of 5–7 μm provide lasing in the continuous-wave mode at room temperature in the region of 850 nm with threshold currents no higher than 0.5 mA, a differential efficiency no lower than 0.6 W/A, a modulation frequency as high as 20 GHz, and a MCEF factor of ～10 GHz/mA^1/2.