H. E. Scheibler

Bio: H. E. Scheibler is an academic researcher from Novosibirsk State University. The author has contributed to research in topics: Surface states & Surface photovoltage. The author has an hindex of 6, co-authored 14 publications receiving 511 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...

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.

Evolution of electronic properties at the p‐GaAs(Cs,O) surface during negative electron affinity state formation

Abstract: The evolution of surface band bending and surface photovoltage was monitored in situ by photoreflectance spectroscopy during activation of the surface of epitaxial GaAs to the state of negative electron affinity by successive deposition of cesium and oxygen in a standard ‘‘yo‐yo’’ technique. Considerable variations of the band bending (by approximately 0.3 eV) and surface photovoltage (by three orders of magnitude) were observed. It was found that the maximum of photoemission quantum yield corresponded to unexpectedly small value of the band bending φs=0.3 eV, as compared to widely accepted value of approximately 0.5 eV.

Spectroscopy of systems with time variable parameters: photoreflectance of GaAs(001) under cesium adsorption.

Abstract: A modification of photoreflectance spectroscopy, which improves the precision and efficiency of measuring time-evolving surface electric fields, is proposed. This modification is explored for studying the band bending evolution under cesium adsorption on the reconstructed GaAs(001) surface and relaxation processes in the non-equilibrium adsorbate overlayer. Observation of several distinct maxima and minima in the coverage dependence of the band bending can be explained by the formation of adatom-induced surface states with a quasi-discrete spectrum.

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.

Franz–Keldysh oscillations in modulation spectroscopy

Abstract: In the presence of an electric field, the dielectric constant of a semiconductor exhibits Franz–Keldysh oscillations (FKO), which can be detected by modulated reflectance. Although it could be a powerful and simple method to study the electric fields/charge distributions in various semiconductor structures, in the past it has proven to be more complex. This is due to nonuniform fields and impurity induced broadening, which reduce the number of detectible Franz–Keldysh oscillations, and introduce uncertainties into the measurement. In 1989, a new structure, surface–undoped–doped (s‐i‐n+/s‐i‐p+) was developed, which allows the observation of a large number of FKOs and, hence, permitting accurate determination of electric fields. We present a review of the work on measuring electric fields in semiconductors with a particular emphasis on microstructures using the specialized layer sequence. We first discuss the general theory of modulation techniques dwelling on the approximations and their relevance. The cas...