A. A. Sushkov

Bio: A. A. Sushkov is an academic researcher from N. I. Lobachevsky State University of Nizhny Novgorod. The author has contributed to research in topics: Silicon & Epitaxy. The author has an hindex of 5, co-authored 10 publications receiving 108 citations.

Monolithically integrated InGaAs/GaAs/AlGaAs quantum well laser grown by MOCVD on exact Ge/Si(001) substrate

Abstract: We report on realization of the InGaAs/GaAs/AlGaAs quantum well laser grown by metallorganic chemical vapor deposition on a virtual Ge-on-Si(001) substrate. The Ge buffer layer has been grown on a nominal Si(001) substrate by solid-source molecular beam epitaxy. Such Ge buffer possessed rather good crystalline quality and smooth surface and so provided the subsequent growth of the high-quality A3B5 laser structure. The laser operation has been demonstrated under electrical pumping at 77 K in the continuous wave mode and at room temperature in the pulsed mode. The emission wavelengths of 941 nm and 992 nm have been obtained at 77 K and 300 K, respectively. The corresponding threshold current densities were estimated as 463 A/cm2 at 77 K and 5.5 kA/cm2 at 300 K.

Deep UV narrow-band photodetector based on ion beam synthesized indium oxide quantum dots in Al2O3 matrix

Abstract: Semiconductor quantum dots have attracted tremendous attention owing to their novel electrical and optical properties as a result of their size dependent quantum confinement effects. This provides the advantage of tunable wavelength detection, which is essential to realize spectrally selective photodetectors. We report on the fabrication and characterization of a high performance narrow band ultraviolet photodetector (UV-B) based on Indium oxide (In2O3) nanocrystals embedded in aluminium oxide (Al2O3) matrices. The In2O3 nanocrystals are synthesized in an Al2O3 matrix by sequential implantation of In+ and ions and post-implantation annealing. The photodetector exhibits excellent optoelectronic performances with high spectral responsivity and external quantum efficiency. The spectral response shows a band-selective nature with a full width half maximum of ~60 nm, and a responsivity reaching up to 70 A W−1 under 290 nm at 5 V bias. The corresponding rejection ratio to visible region was as high as 8400. The high performance of this photodetector makes it highly suitable for practical applications such as narrow-band spectrum-selective photodetectors. The device design based on ion-synthesized nanocrystals could provide a new approach for realizing a visible-blind photodetector.

Light-emitting 9R-Si phase formed by Kr+ ion implantation into SiO2/Si substrate

Abstract: Light-emitting layers of hexagonal 9R silicon were synthesized by ion implantation into SiO2/Si substrates. Using cross-sectional transmission electron microscopy, the formation of a 9R phase in a cubic silicon substrate near the interface with silicon dioxide under irradiation with Kr+ ions (80 keV) and subsequent annealing at 800 °C is demonstrated. Arguments explaining how the new phase is formed through hexagonalization of the initial cubic silicon are presented. The synthesized 9R-Si layers are characterized by a low-temperature photoluminescence line with the maximum at a wavelength around 1240 nm. First-principles calculations of the 9R-Si electronic band structure showed that this material is an indirect-gap semiconductor with the bandgap value of 1.06 eV, which is in good agreement with the spectral position of the experimentally observed photoluminescence line. Believing that the proposed approach can be extended to other semiconductors, we calculated the electronic band structure of 9R germanium and predicted that the hexagonalization converts cubic Ge into a direct-gap semiconductor with the bandgap of 0.48 eV.Light-emitting layers of hexagonal 9R silicon were synthesized by ion implantation into SiO2/Si substrates. Using cross-sectional transmission electron microscopy, the formation of a 9R phase in a cubic silicon substrate near the interface with silicon dioxide under irradiation with Kr+ ions (80 keV) and subsequent annealing at 800 °C is demonstrated. Arguments explaining how the new phase is formed through hexagonalization of the initial cubic silicon are presented. The synthesized 9R-Si layers are characterized by a low-temperature photoluminescence line with the maximum at a wavelength around 1240 nm. First-principles calculations of the 9R-Si electronic band structure showed that this material is an indirect-gap semiconductor with the bandgap value of 1.06 eV, which is in good agreement with the spectral position of the experimentally observed photoluminescence line. Believing that the proposed approach can be extended to other semiconductors, we calculated the electronic band structure of 9R germaniu...

Electrically pumped InGaAs/GaAs quantum well microdisk lasers directly grown on Si(100) with Ge/GaAs buffer.

Abstract: In this work we report, to the best of our knowledge, the first quantum well electrically-pumped microdisk lasers monolithically deposited on (001)-oriented Si substrate. The III-V laser structure was epitaxially grown by MOCVD on silicon with an intermediate MBE-grown Ge buffer. Microlasers with an InGaAs/GaAs quantum well active region were tested at room temperature. Under pulsed injection, lasing is achieved in microlasers with diameters of 23, 27, and 31 µm with a minimal threshold current density of 28 kA/cm2. Lasing spectrum is predominantly single-mode with a dominant mode linewidth as narrow as 35 pm.

Stochastic resonance in a metal-oxide memristive device

Abstract: The stochastic resonance phenomenon has been studied experimentally and theoretically for a state-of-art metal-oxide memristive device based on yttria-stabilized zirconium dioxide and tantalum pentoxide, which exhibits bipolar filamentary resistive switching of anionic type The effect of white Gaussian noise superimposed on the sub-threshold sinusoidal driving signal is analyzed through the time series statistics of the resistive switching parameters, the spectral response to a periodic perturbation and the signal-to-noise ratio at the output of the nonlinear system The stabilized resistive switching and the increased memristance response are revealed in the observed regularities at an optimal noise intensity corresponding to the stochastic resonance phenomenon and interpreted using a stochastic memristor model taking into account an external noise source added to the control voltage The obtained results clearly show that noise and fluctuations can play a constructive role in nonlinear memristive systems far from equilibrium

Noise-assisted persistence and recovery of memory state in a memristive spiking neuromorphic network

Abstract: We investigate the constructive role of an external noise signal, in the form of a low-rate Poisson sequence of pulses supplied to all inputs of a spiking neural network, consisting in maintaining for a long time or even recovering a memory trace (engram) of the image without its direct renewal (or rewriting). In particular, this unique dynamic property is demonstrated in a single-layer spiking neural network consisting of simple integrate-and-fire neurons and memristive synaptic weights. This is carried out by preserving and even fine-tuning the conductance values of memristors in terms of dynamic plasticity, specifically spike-timing-dependent plasticity-type, driven by overlapping pre- and postsynaptic voltage spikes. It has been shown that the weights can be to a certain extent unreliable, due to such characteristics as the limited retention time of resistive state or the variation of switching voltages. Such a noise-assisted persistence of memory, on one hand, could be a prototypical mechanism in a biological nervous system and, on the other hand, brings one step closer to the possibility of building reliable spiking neural networks composed of unreliable analog elements.

Ultra-low threshold InAs/GaAs quantum dot microdisk lasers on planar on-axis Si (001) substrates

Abstract: Monolithic integration of efficient III–V light-emitting sources on planar on-axis Si (001) has been recognized as an enabling technology for realizing Si-based photonic integrated circuits (PICs). The field of microdisk lasers employing quantum dot (QD) materials is gaining significant momentum because it allows massive-scalable, streamlined fabrication of Si-based PICs to be made cost effectively. Here, we present InAs/GaAs QD microdisk lasers monolithically grown on on-axis Si (001) substrate with an ultra-low lasing threshold at room temperature under continuous-wave optical pumping. The lasing characteristics of microdisk lasers with small diameter (D) around 2 μm and sub-wavelength scale (D∼1.1 μm) are demonstrated, with a lasing threshold as low as ∼3 μW. The promising lasing characteristics of the microdisk lasers with ultra-low power consumption and small footprint represent a major advance towards large-scale, low-cost integration of laser sources on the Si platform.

Designing a bidirectional, adaptive neural interface incorporating machine learning capabilities and memristor-enhanced hardware

Abstract: Building bidirectional biointerfaces is one of the key challenges of modern engineering and medicine, with dramatic potential impact on bioprosthetics. Two of the major challenges of biointerface design concern signal stability and power efficiency. The former entails: a) ensuring that biosignal inputs corresponding to the same ground truth (e.g. patient “intentions”) are recorded and interpreted consistently and b) maintaining the mapping from biointerface stimulation outputs to behavioral outputs (e.g. muscle movements). In this work we demonstrate how machine learning techniques, state-of-art nanoelectronics and microfluidics can combine forces to build and test low-power, adaptable biointerfaces that address both key challenges. Specifically, we demonstrate that: 1) we can emulate the input/output transfer characteristics of a structure biological neural network (BNN) with an artificial one (ANN), 2) it is possible to translate the resulting, “ideally trained” ANN into a hardware network using RRAM devices as synapses without significant loss of accuracy, despite concerns in the community about RRAM device reliability and 3) using a very simple mechanism of shifting the active stimulation electrode can fully restore functionality after the initial stimulation site degrades, prolonging the usable lifetime of the biointerface significantly. In this manner we place a key stepping stone towards building self-adjusting, low-power biointerfaces, themselves a foundational stepping stone towards adaptable, low-power bioprostheses.