A. S. Jaroshevich

Bio: A. S. Jaroshevich is an academic researcher from Russian Academy of Sciences. The author has contributed to research in topics: Electron & Band gap. The author has an hindex of 8, co-authored 22 publications receiving 566 citations.

Long term operation of high quantum efficiency GaAs(Cs,O) photocathodes using multiple recleaning by atomic hydrogen

Abstract: Atomic hydrogen, produced by thermal dissociation of H2 molecules inside a hot tungsten capillary, is shown to be an efficient tool for multiple recleaning of degraded surfaces of high quantum efficiency transmission-mode GaAs photocathodes within an ultrahigh vacuum (UHV) multichamber photoelectron gun. Ultraviolet quantum yield photoemission spectroscopy has been used to study the removal of surface pollutants and the degraded (Cs,O)-activation layer during the cleaning procedure. For photocathodes grown by the liquid-phase epitaxy technique, the quantum efficiency is found to be stable at about 20% over a large number of atomic hydrogen cleaning cycles. A slow degradation of the quantum efficiency is observed for photocathodes grown by metal-organic chemical vapor deposition, although they reached a higher initial quantum efficiency of about 30%–35%. Study of the spatial distributions of photoluminescence intensity on these photocathodes proved that this overall degradation is likely due to insertion o...

Preparation and performance of transmission-mode GaAs photocathodes as sources for cold dc electron beams

Abstract: Photoemission from GaAs cathodes with negative electron affinity (NEA) is applied for producing electron beams with very low longitudinal and transverse velocity spread. GaAs transmission-mode cathodes were activated with Cs and either O2 or NF3 in an extremely high vacuum setup (base pressure below 10−12 mbar). Quantum efficiencies of 20%–25% (at 670 nm) and long dark lifetimes (about 1000 h) could be achieved for both types of activation in a reproducible way. Using a method based on the adiabatic transverse expansion of an electron beam in a spatially decreasing magnetic field, the mean transverse energy (MTE) of the photoemitted electrons was measured systematically, recording longitudinal energy distribution curves. Both the MTE and the longitudinal energy spread strongly depend on the value of NEA and the position of the extracted distribution relative to the bulk conduction band minimum. Electrons with energies above the conduction band minimum are thermalized with the lattice temperature of the cathode, while electrons with energies below this level show a non-Maxwellian distribution with enhanced transverse energies. Thus, when extracting all electrons in a current limited emission mode, the MTE increases with the absolute value of NEA and reaches values up to ≈100 meV. By cutting off the low energy electrons with an external potential barrier, the longitudinal as well as transverse energy spread of the extracted electron ensemble are reduced. The MTE could be reduced down to about 28 meV at room temperature and to about 14 meV at liquid nitrogen temperature. The behavior of the MTE was found equivalent for (Cs, O) and for (Cs, F) activation layers on the same cathode. Conclusions about energy loss and scattering in the emission of photoelectrons from NEA GaAs cathodes are discussed.

Determination of built-in electric fields in delta-doped GaAs structures by phase-sensitive photoreflectance

Abstract: Built-in interface electric fields in MBE-grown delta-doped and other layered structures were studied by a modification of photoreflectance spectroscopy, which allowed us to separate contributions originating from various regions of the structures. The modification explores differences in temporal responses of photoreflectance contributions and the respective differences in the phase shift between photoreflectance signal and modulated pump. Proper selection of modulation frequency and phase angle of a phase-sensitive detector allowed us to suppress one of the contributions and to extract the other. The proposed technique of phase separation, along with the Fourier analysis of Franz-Keldysh oscillations, enabled us to obtain quantitatively defined energy band diagrams of delta-doped and SIN+ structures. It was found that Fermi level is pinned by the interface states both at the GaAs undoped buffer/semiinsulating substrate interface and at the n+-GaAs buffer/n+-GaAs substrate interface. These interface states are presumably due to defects which arise at the initial stages of the molecular beam epitaxy.

Fourier resolution of surface and interface contributions to photoreflectance spectra of multilayered structures

Abstract: A technique for the determination of built-in electric fields by Fourier transformation of Franz-Keldysh oscillations in photoreflectance (PR) spectra is developed. This technique can be used for the resolution of mixed PR spectra originating from the surface and buried interfaces of layered semiconductor structures. Fourier transformation is especially effective in combination with phase-resolved photo-reflectance, which allows to change the relative amplitude of different PR spectral components. Model MBE-grown GaAs structures with uniform surface electric fields are investigated. Along with the surface PR component, a component originated from the buffer substrate interface is extracted by Fourier transformation and phase resolution techniques. The energy band diagram of the structure is reconstructed. The Fermi level is shown to be pinned at the buffer substrate interface by defect-induced electronic states.

Band parameters for III–V compound semiconductors and their alloys

Abstract: We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Nano‐photocatalytic Materials: Possibilities and Challenges

Abstract: Semiconductor photocatalysis has received much attention as a potential solution to the worldwide energy shortage and for counteracting environmental degradation. This article reviews state-of-the-art research activities in the field, focusing on the scientific and technological possibilities offered by photocatalytic materials. We begin with a survey of efforts to explore suitable materials and to optimize their energy band configurations for specific applications. We then examine the design and fabrication of advanced photocatalytic materials in the framework of nanotechnology. Many of the most recent advances in photocatalysis have been realized by selective control of the morphology of nanomaterials or by utilizing the collective properties of nano-assembly systems. Finally, we discuss the current theoretical understanding of key aspects of photocatalytic materials. This review also highlights crucial issues that should be addressed in future research activities.

Modeling elastic and plastic deformations in nonequilibrium processing using phase field crystals.

Abstract: A continuum field theory approach is presented for modeling elastic and plastic deformation, free surfaces, and multiple crystal orientations in nonequilibrium processing phenomena. Many basic properties of the model are calculated analytically, and numerical simulations are presented for a number of important applications including, epitaxial growth, material hardness, grain growth, reconstructive phase transitions, and crack propagation.