Atsuko Ebina

Electronic surface states of II–VI compound semiconductors

Abstract Recent studies of electronic surface states of II–VI compounds are reviewed. The chemical composition and stoichiometry of the (110),{111} or {0001}, and (100) surfaces are described. Low-energy-electron diffraction (LEED) studies of relaxations of the (110) or (10 1 0) surface are stated briefly. The calculated surface electronic structure of ZnSe(110) is compared with an experimental result given by angle-resolved photoemission energy-distribution curves. A summary of locations of the empty dangling-bond state of the (110) and (0001) surfaces predicted by electron-energy-loss spectroscopy is given. Photoemission studies of ZnSe(110)-O2 and ZnTe(110)-O2 are described.

Crystal Structure and Stacking Disorder of ZnS Single Crystals Grown from the Melt

The crystal structure of ZnS single crystals grown from melt has been found to be cubic zinc blende by the x‐ray analysis of oscillation photographs. However, the x‐ray 〈111〉 axis oscillation patterns of the crystals synthesized by various methods are symmetric about the equator line and some spots are elongated along c*, whereas the patterns of natural crystals are asymmetric and sharp. Therefore, it is concluded that the synthetic ZnS crystal contains a considerable amount of stacking disorder in the close‐packed planes due to growth faults which result in two orientations in the crystal structure (twin orientations) that repeat with a relatively short periodicity. The value of fault probability occurring in the (111) plane can be obtained by superimposing the observed diffuse diffraction spectra with the ones calculated numerically by a formula proposed by Paterson for the growth fault. This value is also compared with that obtained from the transmission electron micrographs.

Crystal growth of ZnxCd1−xTe solid solutions and their optical properties at the photon energies of the lowest band‐gap region

Single crystals of ZnxCd1−xTe solid solutions have been grown from a melt under an Ar pressure of about 50 atm. The crystals of uniform composition were grown over the whole range of molar composition, when the crystal growth was performed in excess Zn and/or Cd. A grown boule of 30 × 15 mm φ contained several single‐crystal domains of size 7 × 5 × 5 mm. On the basis of Vegards law, the molar composition x was determined from x‐ray measurements of lattice constants. The variation of x throughout a single‐crystal domain was found to be less than ± 1%. Optical experiments including transmittance and reflectance measurements have been made on the cleaved (110) planes at room temperature. The variation of the lowest band gap with x was determined from the peak positions in the reflectivity spectra. The bowing parameter, which is a measure of the deviation from the linear change, of this gap was found to be 0.33 eV.

Reflectivity spectra of ZnxCd1−xTe single crystals

Abstract Reflectivity measurements of the Zn x Cd1− x Te alloys were made from 2.0 to 6.2eV at room temperature. The assignments of the structures in the reflectivity spectra are made on the basis of the band gap assignments of ZnTe and CdTe. The E0, e1, and E1 gap including its spin-orbit splitting gap show the quadratic variation with molar composition, x, whereas the other gaps vary nearly linearly with x or are approximately independent of x.

Surface barriers formation mechanism of the chemically etched CdTe(111) polar surfaces and gold interfaces

Abstract Surface barriers of gold on chemically etched CdTe(111) polar surfaces are studied. Polarities are examined from chemically etched pits patterns with the references. AFM observations of the mirror etched surfaces show the same morphologies on both polarities. Barrier characteristics are evaluated with the current-voltage characteristics. The barriers on (111)A surfaces show nearly ideal Schottky barrier properties but the barriers on (111)B surfaces show the current transport characteristics of recombination preferred properties. XPS analysis on the barrier aged in atmospheric circumstances for one year shows the topmost atomic constitutions as follows. (111)A surfaces are covered with chemically bonded Cd atoms and O atoms. Continuous Ar ion etching intensified signal from Cd atoms and decrease in adsorbed O atoms, but no clear signals from chemically bonded Te atoms are detected. Topmost (111)B surfaces are covered with Cd atoms and chemically bonded Te atoms with O atoms. Continuous Ar ion etching shows more Cd, Te atoms and less adsorbed O atoms. It is considered that the different surface barrier properties of the CdTe(111) are due to the difference of the atomic configurations.

Oxide-layer formation on the ZnSe (110) surface studied by LEED intensity measurements

Abstract Oxidation of the vacuum cleaved ZnSe (110) surface by electron-beam irradiation during the course of LEED measurements leads to a formation of bulklike ZnO layers. The LEED pattern and the I–V profile from the oxide overlayer confirm the presence of the ZnO (0001) layer which is inclined at an angle of 30° from the (110) substrate and has a near orientation of the (111) plane of the substrate crystal.

Effect of Secondary Infrared Irradiation on the Photoelectron Energy Distribution Curve of Cesiated Silicon

Effects of secondary ir irradiation of which photon energy is slightly higher than the indirect band‐gap energy on photoemissive properties of cesiated Si crystals are given. Measurements were made for p+‐, p‐, and n‐type cesiated Si. In the case of the samples which had absorbed metallic cesium by the ampoule method, it was observed that the ir irradiation had little or no effect on the quantum yield of the photoemission for all types of samples, but did cause a shift of the photoemitted EDC (energy distribution curve) towards higher electron energy and at times narrowing of EDC for p+‐ and p‐type samples. ir irradiation had no effect on the n‐type sample. Maximum shift of the low‐energy cutoff of EDC was observed for the ir of 1.25 eV, and it was about 0.4 eV. By the analysis of the ir effect on the photoemitted EDC, the electron escape length was estimated to be about 65–75 A for photoelectrons excited by a light of 2.6–3.4 eV.