Home – Home – Jornals – Avtometriya 2020 number 5

Three modes of the kinetics of the Si(111) surface etching by a selenium molecular beam have been distinguished by in situ ultrahigh vacuum reflection electron microscopy. At low temperatures (≲650 °C, depending on the Se deposition rate), the etching kinetics is limited by the energy of SiSe2 molecule formation and desorption, and the surface is completely covered with an impurity-induced “1×1”-Se phase of silicon selenide. In the temperature range of ~700-1100 °C, the etching rate is limited by the deposited Se flux and does not depend on the temperature, surface structure, and etching mechanism (step flow or periodic 2D island nucleation). At high temperatures (≳1150 °C), sublimation of Si atoms starts to make the major contribution to the silicon flux from the surface. We have formulated a theoretical model that describes the temperatures and the kinetics of the transitions between the etching modes.

An overview of the current state, problems and their solutions, as well as the potential for the development of the molecular beam epitaxy (MBE) technology for obtaining CdHgTe structures on various substrates for infrared detectors is proposed. The data on ultra-high vacuum MBE sets and equipment for monitoring the growth processes for different substrates, preparation of surface substrates, growth of buffer layers on alternative substrates, and growth and doping of CdHgTe layers are reported. Basic structural defects, such as dislocations and macrodefects, and the minimum achieved levels of their concentration, which limit the quality of the detectors, are presented. The data on the problems of external doping of CdHgTe layers and resultant electrophysical parameters of such layers are considered. The photovoltaic parameters of IR detectors are presented; they are close to theoretical predictions and show that the MBE technology is ready for production of CdHgTe/Si structures on substrates six inches in diameter. The results of research and development of the growth and doping processes of CdHgTe structures on GaAs and Si substrates 76.2 mm in diameter at the Rzhanov Institute of Semiconductor Physics SB RAS are demonstrated.

This paper presents the results of a study of the formation of stressed nanoheterostructures based on compounds of group 4 materials (Ge, Si, and Sn). The mechanisms of diffusion of silver, tin, and lead atoms over the surface are established, and the temperature dependences of the diffusion coefficients of these elements are derived. It is shown that the diffusion of silver, tin, and lead atoms proceeds by the mechanism of solid-phase spreading with the formation of surface phases. Experimental data that indicate the predominant role of edge dislocations and edge-type dislocation complexes in relaxation of the Ge/Ge_0,5Si_0,5/Si(001) heterostructure are presented. Tin-rich islands with a Si pedestal on a Si(100) substrate are obtained by molecular beam epitaxy. Initially, an Sn film is applied to the Si surface. During subsequent annealing, an array of Sn islands is formed, which are used as catalysts for the growth of nanoobjects. The tin-rich islands with a Si pedestal are formed after silicon deposition at temperatures of 300-450ºC on the surface with Sn islands. The growth of the islands with the pedestal occurs by the vapor-liquid-solid mechanism. Intense photoluminescence is detected from the tin-rich islands with the Si pedestals in the wavelength range of 1.3-1.7 microns.

In new pHEMT heterostructures with donor-acceptor doping, the confinement of the two-dimensional electron gas is enhanced by increasing potential barriers. In turn, this makes it possible to practically double the concentration of 2DEG in the QW without the emergence of parasitic parallel conductivity and to increase the saturated drift velocity in a high electric field by a factor of 1.2-1.3. As a result, the output power density of the transistors could be increased by more than 50% as compared to the best values.

The present study deals with the structurally perfect high-resistance GaN layer growth ability by the ammonia molecular beam epitaxy technique. The results allow forming SiN/Al (Ga)N/GaN heterostructures for transistors with high electron mobility. In this work, the conditions for growing GaN layers with a smooth surface morphology (RMS ~ 2 nm) suitable for creating sharp heterojunctions are determined, and a possibility of improving the GaN layer crystal perfection is demonstrated using a high-temperature (growth temperature more than 940 °С) buffer AlN layer. It is shown that in situ passivation of the Al(Ga)N/GaN heterostructure surface with an ultrathin SiN layer results in the formation of normally closed transistors with low competitive values of the current collapse (~ 1%).

The influence of various Hg_1-xCd_xTe surface treatments prior to Al₂O₃ atomic layer deposition (ALD) on the interface charge density has been investigated. MIS structures with different surface pretreatments have been fabricated. The voltage-capacitance current-voltage characteristics have been measured, and the interface charge density has been calculated. Films with the surface composition х=0.22 with natural oxide have a nonuniform charge distribution over the surface varying within (0.8÷1.8)×10^-8 Q/cm², which can cause inversion of the conductivity type near the surface. Treating MCT films with Hg vapor at room temperature causes negative charge formation in the interval (0.4÷1.6) ×10^-8 Q/cm².

The influence of the growth rate (flux density of In atoms) on the composition of InAs_xSb_1-x(100) solid solutions during molecular beam epitaxy (MBE) with As₂ and Sb₄ fluxes is experimentally investigated. It is found that an increase in the growth rate at constant ratios of the As₂ to Sb₄ fluxes and of the In atoms flux to the total flux of the V group molecules leads to a decrease in the arsenic fraction in the solid solution. It is shown that the growth rate is an independent parameter of the MBE process, which determines the composition of InAs_xSb_1-x solid solutions. A mechanism for the formation of the solid solution composition is proposed, which explains the role of the growth rate.

This paper provides an overview of recent results and new data on the study of the optical response of semiconductor nanocrystals obtained using plasmon-enhanced optical spectroscopies, including the surface-enhanced Raman scattering (SERS) and surface-enhanced IR absorption (SEIRA). These methods are based on enhancement of the phonon response of semiconductor nanocrystals placed in the field of localized surface plasmon resonance (LSPR) of metal nanostructures. Due to a proper choice of a certain morphology of metal nanostructures, the LSPR energy coincides with the laser excitation energy and/or the energy of optical phonons in nanocrystals. The resonant conditions provide a significant increase in local electric fields and, as a result, a sharp increase in the Raman signal and IR absorption at the frequencies of surface optical phonons of nanocrystals. Enhancement of the optical response makes it possible not only to detect monolayer coatings of nanocrystals, but also to study their crystal structure, phase and elemental composition, and internal mechanical stresses. Utilization of the Raman spectroscopy in combination with atomic force microscopy has opened up new possibilities for analyzing the vibrational and electronic spectra of nanocrystals with nanometer spatial resolution.

A brief overview of experimental and theoretical studies on using single neutral atoms trapped in arrays of optical dipole traps as qubits of a quantum computer is presented. Methods of loading and detection of atoms in the traps and of implementing two-qubit quantum gates via dipole-dipole interaction at short-term laser excitation of atoms to Rydberg states are discussed.

The paper describes the operating principles of subminiature semiconductor emitters and offers the research results on the performance for those emitters that were developed and manufactured at the Rzhanov Institute of Semiconductor Physics of the Siberian Branch of the Russian Academy of Sciences over the last three years. A single photon emitter based on Al_xIn_1-xAs/Al_yGa_1-yAs quantum dots has been developed. Results of developing single-mode vertical-cavity surface-emitting lasers with a wavelength of 794.8 nm oriented for future application in the chip-scale atomic clock and operating at the transition 5S1/2→5P1/2 of Rb⁸⁷ atoms are reported.

The paper presents a review of the design and manufacturing technology, methods and results of studying the optical spectra and reflection kinetics of coupled quantum wells A₃B₅ with thin barriers, as well as the results of using optical shutters developed on their basis to synchronize the modes of a Yb³⁺:KY(WO₄)₂ femtosecond laser with a high (about 1 GHz) pulse repetition rate.

It is shown that investigations of self-organization and morphological rearrangements on an atomically clean Si(111) surface by in situ ultrahigh vacuum reflection electron microscopy ensure understanding of fundamental processes that can be applied in metrology. By means of high-resolution electron microscopy, a natural oxide formed on the Si(111) surface under ambient conditions is shown to replicate the height of an atomic step with high accuracy. Based on this fact, we have developed methods for creating measures of vertical dimensions in the 0.31-31 nm range with an error of less than 0.05 nm in the entire measurement range. It is shown that it is possible to create extremely wide “atomically smooth” surfaces (up to 230 μm) and to use them as reference mirrors in interferometric microscopes. Crystalline samples containing a verified number of monoatomic steps and “atomically smooth” surface areas are included into the State Secondary Standard as a measure of height and flatness in the angstrom range.

A review of recent research performed at the Laboratory of Theoretical Physics of the Rzhanov Institute of Semiconductor Physics of the Siberian Branch of the Russian Academy of Sciences is presented. Two directions of research are discussed: the transport properties of two-dimensional excitonic systems and transport of electrons in two-dimensional topological insulators. Significant attention is paid to excitonic systems in the regime of the Bose-Einstein condensation and to the theory of electrical conductivity in two-dimensional topological insulators with the close-to-critical sample thickness, which is induced by the branched network of edge states penetrating through the sample.

The characteristics of MIS structures based on insulating PbSnTe:In films grown by molecular beam epitaxy (MBE) with compositions near the band inversion are studied. It is shown that a number of their features can be induced by a ferroelectric phase transition with the Curie temperature in the range of 15-20 K. The injection and detection of spin-polarized electrons in PbSnTe:In are studied by using ferromagnetic contacts Co and Co₄₀Fe₄₀B₂₀. A spin-valve effect is discovered by measuring the magnetoresistance in local geometry at a distance of more than 30 μm from ferromagnetic contacts. The presence of a surface spin-polarized state with a linear dispersion law is demonstrated by means of the photoemission with angular and spin resolution.