Subjects
The Center is having carried out the basic and applied research in the following directions 4.7 “Hardware components for microelectronics, nanoelectronics, and quantum computers. Materials for micro- and nanoelectronics. Nano- and micro-system engineering. Solid state electronics” and 4.10 “Nanotechnologies, nanobiotechnologies, nanosystems, nanomaterials, nanodiagnostics, nanoelectronics, and nanophotonics” of the Nanotechnology and IT Department of the Russian Academy of Sciences, in accordance with the Program on Basic Research of the Presidium of the Russian Academy of Sciences no. 21 “Grounds of Basic Research of Nanotechnologies and Nanomaterials”, the Research Program of the St. Petersburg Scientific Center of the Russian Academy of Sciences, State Contracts with the Ministry of Science and Higher Education as well as according to commercial contracts and scientific collaboration agreements.
Recent Research Areas and Advantages:
1
Research of mechanisms of the growth of nanostructures in AlInGaN based wide-band compounds by the metal-organic chemical vapor deposition as well as study of their structural and optical properties.
The theoretical grounds of the synthesis of InGaN/(Al)GaN quantum dots in the active region of light-emitting devices have been developed. The epitaxial growth technique of InGaN/AlGaN heterostructures for high-efficiency blue, green, and near UV LEDs has been produced. The structural and optical properties of LED heterostructures with the active region based on super-thin InGaN quantum wells limited by short-period InGaN/GaN superlattices have been suggested and studied. It has been shown that a use of variband short-period superlattices as restrictive layers makes it possible to substantially enhance the quantum efficiency. The optical properties of the structures have been studied under the optical and injection pumping. The pilot LED structures with single super-thin InGaN layers in the active region have been grown and the possibility to obtain appreciable quantum efficiency up to a wavelength of 560 nm has been demonstrated.
2
ИStudy of the light generation and reemission in AlInGaN nanoheterostructures with a set of the quantum wells with various depths. Development of light-emitting nanoheterostructures for UV, blue, and green LEDs as well as for monolithic white LEDs.
Comprehensive studies including the choice of an optimal internal design of a blue LED heterostructure (sequence, thickness, composition of separate layers, and doping profiles) for implementation of the maximum internal quantum efficiency and effective light extraction from a chip have been carried out to obtain effective LED heterostructures that can operate at high working current densities. The performed experiments to optimize the design of heterostructures were based on the comprehensive numerical simulations of their electrical and optical properties. Light-emitting nanoheterostructures for near UV (350-380 nm) LEDs have been optimized using the GaN quantum wells in the AlGaN matrix. This allowed us to obtain the active regions of LED heterostructures with a wavelength less than 365 nm. The LED heterostructure with the active region based on super-thin InGaN quantum wells restricted by short-period InGaN/GaN superlattices from both sides has been suggested for high-power blue (440-470 nm) LEDs.
The pilot LED heterostructures containing single super-thin InGaN layers with a high content of In has been grown and the possibility to obtain radiation with high efficiency up to deep green range of 540-560 nm has been shown.
The nanoheterostructures with two InGaN quantum wells that are separated by the short-period InGaN/GaN superlattice and emit in the blue and green spectral range have been produced. The experimental samples of monolithic dichromic white light sources have been fabricated using these heterostructures.
3
Study of the mechanisms to form narrow-gap band nanoheterostructures based on InP, GaSb, InAs, InSb, and their solid solutions by the MOCVD.
The processing techniques of growth of heterostructures by the MOCVD have been developed to fabricate optoelectronic devices that can operate in the near and middle IR spectral range (1.0–4.5 µm). These devices can be used as photodetectors for infrared imagers and thermal photo transducers as well as for conversion of long-wavelength light in the inverters of solar cell arrays, which will allow one to increase the total efficiency up to 35%. Moreover, laser diodes and lasers can be fabricated using the developed heterostructures.
The processing procedures to grow SiC epitaxial layers on SiC and Si substrates are studied. The technique for growth of Si and SiC powders has been developed. These powders can be used as luminescent markers in medicine research since they are chemically inert in biological environment.
4
Development of the diagnostics of thermal processes in high-power micro- and optoelectronic nanoheterostructure based devices by the IR microscopy. Simulations and experimental study of the thermal processes in high-power light-emitting devices based on semiconductor nanoheterostructures.
The method to obtain digital IR (2.5–3 µm) imagers of semiconductor heterostructures with a high spatial resolution has been developed. The considerable thermal gradients over the p-n-junction area were registered using the IR microscopy in high-power LEDs based on InGaN quantum-well heterostructures. The local overheating can be much more than the mean temperature of the active region, which is determined using the shift of electrical or spectral characteristics. The numerical model has been developed to calculate the current density distribution over the p-n-junction area in high-power LED flip-chips. The model is based on the calculations of potentials and currents in the 3D net of resistances by means of solving the system of linear Kirchhoff equations. The thermal processes in high-power LEDs have been experimentally studied using the temperature dependences of electrical and spectral characteristics as well as the direct temperature mapping. A strong correlation between the experimental distributions of temperature fields and calculated current density distributions in the vertical and flip-chip InGaN LEDs has been revealed.
5
Comprehensive study of the degradation mechanisms in high-efficiency LEDs based on the quantum-well nanoheterostructures.
The structural properties of nanomaterials have been studied using the diffraction analysis, transmission electron microscopy, and multifractal parameterization. It has been revealed that the system of extensive defects, which includes dislocations, their agglomerations as well as dilatation and dislocation interfaces, is the main channel of nonradiative loss. The recombination properties of this system change with increasing the concentration of non-equilibrium carriers, which gives a contribution into the external quantum efficiency droop at current densities higher than 10 A/cm2. It has been shown the validity of the low-frequency noise theory for InGaN/GaN LEDs. It has been found that the dependences of spectral density (S) of low-frequency noise on the current density (I) provide the information on the behavior and status of a defect system (DS) in InGaN/GaN LEDs during their operation and can be used for development the methods of detection of failure-prone LEDs.
