Shigeru Yasuami

Growth temperature dependent atomic arrangements and their role on band-gap of InGaAlP alloys grown by MOCVD

Detailed observation of atomic arrangement in In0.5(Ga1−xAlx)0.5P(0⩽x⩽1) grown by MOCVD with a wide range of growth temperatures Tg (570–770° C) was carried out using electron diffraction and high resolution transmission electron microscopy. A correlation between the atomic arrangement and band-gap energy was studied by photoluminescence and photoacoustic spectroscopy. For Tg≲760° C, the epitaxial layers have ordered structures. For Tg≳770° C, the ordering disappear. Shifts in the band-gap depend on the density of the ordered layers for x≲0.5. For x≳0.5, the band-gap is not affected by the ordering.

Observation of small defects in silicon crystal by diffuse x‐ray scattering

Two kinds of diffuse x‐ray scattering due to defects were observed from a very perfect silicon single crystal. One forms the shape of a cigar, elongated along the [111] direction, and the other is a disk, which is broad and perpendicular to the [111] direction. The cigar‐shaped diffuse scattering is asymmetric around the 111 relp with respect to the Bragg peak. Fourier transforms reveal two types of defects; platelike defects [200 A (φ) ×30 A (t)] of vacancy type and needlelike defects (400 A (l)). The platelike defect dimensions are in fairly good agreement with those of B‐swirl defects observed by de Kock et al. The platelike defects also have a close correlation with the crystal pulling direction. They are contained predominantly in the (111) planes for a crystal grown along the [111] direction.

Wavelength-Dispersive Total Reflection X-Ray Fluorescence with High-Brilliance Undulator Radiation at SPring-8

Wavelength-dispersive total reflection X-ray fluorescence (WD-TXRF) equipment supported by an energy-dispersive (ED) solid-state detector (SSD) has been developed and installed in the BL16XU Industrial Consortium ID Beamline for Material Research at the SPring-8 synchrotron radiation research facility. Equipment specifications are given and results from our initial experiment are discussed in this paper. In the experiment on the sensitivity of detection of metallic impurities on a Si wafer, the lower limit of detection (LLD) using a Ge-SSD reached an order of 108 atoms/cm2 with a corresponding absolute weight of approximately 10 fg for ED-TXRF. In comparison, an order of 109 atoms/cm2 with a corresponding weight of around 100 fg was obtained for WD-TXRF for the first time. Although ED-TXRF still has a lower LLD, using WD-TXRF can provide good energy resolution with a high count rate, opening up a new field of X-ray fluorescence measurement.

Lattice Bending in LEC-Grown Semi-Insulating GaAs Wafers

Lattice bending in LEC-grown semi-insulating GaAs crystal wafers was investigated by X-ray diffraction. Various distributions in the lattice bending were observed in wafers from different boules. Prominent bends, with radii of curvature of about 20 m, were observed at places where the relevant topographs showed the presence of fine cellular dislocation networks. The apparent wafer bending was also examined optically and was found to be caused mainly by back surface damage.

Characterization of polished (111) silicon crystal surface by diffuse x‐ray scattering

The diffuse x‐ray scattering due to small defects in a silicon single crystal, which has been found by Yasuami, Harada, and Wakamatsu [J. Appl. Phys. 50, 6860 (1979)] has been identified as coming from a thin surface layer of the crystal. The small defects, therefore, cannot be B‐swirl defects and do not have any correlation with crystal growth methods, floating zone or Czochralski zone, and with growth direction. They are considered to be introduced during the surface polishing process and to exist in the surface layer of about 150 μm thick. For detecting such small defects, diffuse x‐ray scattering is more advantageous than the conventional rocking curve measurement.

Lattice spacings of LEC-grown and MLEC-grown GaAs crystals

Abstract Lattice spacings ( d ) were measured with an accuracy of 5.9 x 10 -6 in terms of Δ d / d , using a diffractometer with a Si monolithic monochromator. For crystals with 10 4 -10 5 cm -2 order of dislocation density, the lattice spacing varied in the 10 -5 order of magnitude. This variation was attributed to the residual strains in the crystals. There was no definite evidence to prove that lattice spacings depend either on initial melt compositions or on dislocation density.

A precision Bond method with SR

A system for a very high precision absolute lattice spacing measurement has been developed. It employs, in principle, a bond method using a highly collimated and a very narrow bandwidth beam available from a monolithic (+, +) monochromator. Owing to the temperature stabilization of the hutch, where the equipment is installed, it has routinely achieved a precision of 2 parts in 106 in lattice spacing measurements.

Lattice Parameter Measurement of GaAs Crystals Using Monochromatic Synchrotron Radiation

A high-resolution diffractometer with a monolithic Si monochromator was developed for lattice parameter (d) measurements using synchrotron radiation. The accuracy attained was 5.9×10-6 in terms of Δd/d. This degree of accuracy makes it possible to discuss the lattice parameter variation due to composition shifts in GaAs crystals. However, a preliminary study implied that thermally-induced elastic strain affects the lattice parameter more than the material composition shifts for crystals with the 104~105 cm-2 order of dislocation density.

InP-insulator interface structure studied by high resolution transmission electron microscopy

Abstract Interfaces were formed with various insulating materials with different thermal histories. Interface roughening of 5 to ∼30 A was observed. Crystallites (≲ 100 A) at the interfaces were found only when the insulating materials contained Si atoms. Based on these results, a model was proposed, in which crystalline phosphorus grows epitaxially in solid-phase through a reaction between Si atoms and native oxides.

Composition effect on CV profile and threshold voltage for MESFETs fabricated in undoped LEC SI GaAs

A correlation between substrate composition and electrical properties was investigated for undoped LEC SI GaAs crystals. The concentration of residual carbon in a crystal, acting as an acceptor, was found to decrease as the As content increased for As-rich crystals. Consequently, donors in n-active layers were less compensated for and the absolute value of the threshold voltage for MESFETs became higher as the As fraction increased.