Satoshi Komiya

Composition-Modulated Structures in InGaAsP and InGaP Liquid Phase Epitaxial Layers Grown on (001) GaAs Substrates

InGaAsP and InGaP epitaxial layers lattice-matched to (001)-oriented GaAs substrates successfully grown by liquid phase epitaxy have been investigated by transmission electron microscopy, scanning transmission electron microscopy and energy dispersive X-ray spectroscopy. In both layers, periodic diffraction contrasts (modulated structures), are observed in two equivalent directions of the and the . Compositional variation has also been observed along these structures. These are associated with spinodal decomposition of the crystal during growth.

Observation of etch pits produced in InP by new etchants

Abstract New etchants, HBr/HF or HBr/CH 3 COOH, produced sharp etch pits on (100) and (111) slices of InP. The etch pit shape produced on (100) by HBr/HF was pyramidal. The shape on (100) produced by HBr/CH 3 COOH varied from pyramidal to elongated rectangular along 〈110〉 with increasing the composition ratio of CH 3 COOH to HBr. The shape produced on (111)B by HBr/HF or HBr/CH 3 COOH was triangular pyramidal. The etch rates of these new etchants and HBr/H 3 PO 4 were measured as a function of composition ratio at room temperature. The correspondence between pits and dislocations was examined and the results indicated that etch pits produced by these etchants corresponded to dislocations.

High-Density Layer at the SiO2/Si Interface Observed by Difference X-Ray Reflectivity

We have developed a high-accuracy difference X-ray reflectivity (DXR) method using intense synchrotron radiation for the evaluation of ultrathin thermal oxides on Si(100). By carefully analyzing DXR data for gate oxides with thicknesses of 40 A and 70 A grown at 800° C to 1000° C, the existence of a dense ( ~2.4 g/cm3), thin (~10 A) layer at the SiO2/Si interface has been revealed. The thickness of the interfacial layer decreases with increasing oxidation temperature. Oxides grown in O3 or HCl/O2 have a thinner interfacial layer compared to those grown in O2.

Misfit dislocation‐free In1−xGaxAs1−yPy/InP heterostructure wafers grown by liquid phase epitaxy

The conditions to grow misfit dislocation‐free In1−xGaxAs1−yPy/InP (0⩽x⩽0.47, 0⩽y⩽1.0) heterostructure wafers were first determined systematically by observing etch pits and x‐ray topographs. Etch pits were produced on InP substrates on which an In1−xGaxAs1−yPy layer was grown, and they were observed to find whether misfit dislocations generated or not. Threshold regions for initiation of misfit dislocations into the wafers were determined as a function of both lattice misfit and layer thickness. The misfit dislocation‐free regions determined by the etch pit observation of InP was found to be equivalent to the regions where misfit dislocations form in neither InP nor In1−xGaxAs1−yPy . The misfit dislocation‐free regions of the quaternary wafers are larger than the region of the ternary In1−xGaxAs/InP wafers by more than three times.

Catastrophic degradation of InGaAsP/InGaP double‐heterostructure lasers grown on (001) GaAs substrates by liquid‐phase epitaxy

Catastrophically degraded InGaAsP/InGaP double‐heterostructure lasers grown on (001) GaAs substrates by liquid‐phase epitaxy, emitting at 727 and 810 nm are investigated by photoluminescence topography, scanning electron microscopy, transmission electron microscopy, and energy dispersive x‐ray spectroscopy. The degradation is mainly due to catastrophic optical damage at the facet, i.e., development of 〈110〉 dark‐line defects from the facet, and rarely due to catastrophic optical damage at some defects, i.e., development of 〈110〉 dark‐line defects from the defects inside the stripe region. These 〈110〉 dark‐line defects correspond to complicated dislocation networks connected with dark knots, and are quite similar to those observed in catastrophically degraded GaAlAs/GaAs double‐heterostructure lasers. The degradation characteristics of the InGaAsP/InGaP double‐heterostructure lasers are rather similar to those in GaAlAs/GaAs double‐heterostructure lasers concerning the catastrophic degradation.

Transmission electron microscope observation of dark‐spot defects in InGaAsP/InP double‐heterostructure light‐emitting diodes aged at high temperature

Dark‐spot defects revealed in the electroluminescence patterns of degraded InGaAsP/InP double‐heterostructure light‐emitting diodes that are operated at the current density of 8.0 kA/cm2 at 200 °C were investigated using transmission electron microscopy. Bar‐shaped defects lying in the direction of 〈100〉 or 〈110〉 were observed corresponding to the dark defects. These defects were precipitates of a certain kind of metal or compound and not ’’dislocationlike’’ ones.

Thermal oxide growth at chemical vapor deposited SiO2/Si interface during annealing evaluated by difference x-ray reflectivity

The x-ray interference technique has been applied to evaluate the structural changes of high temperature grown chemical vapor deposited (CVD) SiO2 film under several post annealing conditions. In annealing above 800 °C in O2 ambient, a thermal oxide growth has been found at the CVD SiO2/Si interface, and its precise thicknesses have been determined. The estimated diffusion coefficient of the oxidant in CVD film was about three times larger compared to that of thermal oxide. A threshold voltage shift in the oxide was found to strongly correlate to the thickness of the thermal oxide rather than to thermal modifications of the CVD SiO2 itself.

Defect structures in rapidly degraded InGaAsP/InGaP double‐heterostructure lasers

Rapidly degraded InGaAsP/InGaP double‐heterostructure lasers grown on (001)‐oriented GaAs substrates by liquid phase epitaxy have been investigated by photoluminescence topography and transmission electron microscopy. 〈100〉‐dark‐line defects and 〈110〉‐dark‐line defects are observed in the degraded region. The 〈100〉‐dark‐line defects correspond to interstitial type dislocation dipoles caused by recombination enhanced dislocation climb. Their origins are threading dislocations, V‐shaped dislocations, and dislocation networks. The 〈110〉‐dark‐line defects correspond to faulted dipoles extended from small faulted loops in the active layer, edge dipoles extended from threading dislocations, and glide dislocations. The velocities of the 〈100〉‐dark‐line defects are estimated by the operating time and the length of the dark lines, and are quite similar to those in rapidly degraded GaAlAs double‐heterostructure lasers.

Structural fluctuation of SiO2 network at the interface with Si

Abstract We analyzed the density of thermally grownSiO 2 /Siby X-ray reflectivity measurements and local vibration properties by infrared spectroscopy. The macroscopic density varied with growth conditions. A lower growth temperature caused higher film density. We also found a thin (1 nm) and dense (2.35–2.4 g/cm 3 ) transient layer at theSiO 2 /Siinterface. The film density was constant to the thickness direction without the transient layer. On the other hand, IR properties showed characteristic film thickness dependencies. At a film thickness greater than 10 nm, the frequency of the transverse optic (TO) mode of Si-O stretching shifted to the red direction, decreasing with the film thickness; while the frequency of the longitudinal optic (LO) mode is unchanged. This red shift of TO mode has no relation to the film density. At a film thickness of less than 6 nm, we found that both the TO and LO mode shift to the red direction simultaneously. The red shifts gradually increased with decreasing film thickness. This indicates that the SiO 2 network was densified by compressive stress. We assumed that the macroscopic and microscopic fluctuation were related to the oxide growth and formation of a hetero-junction.

Mechanism of catastrophic degradation in 1.3‐μm V‐grooved substrate buried‐heterostructure lasers with the application of large pulsed currents

Catastrophic degradation of V‐grooved substrate buried‐heterostructure InGaAsP/InP lasers (λ=1.3 μm), by large pulsed currents, has been investigated using scanning electron microscopy, etching technique, energy dispersive x‐ray spectroscopy, and spatially resolved photoluminescence topography. After the degradation, the diode stops lasing and becomes ohmic. These are associated with the following phenomena: (i) facet erosion inside or outside the stripe region; (ii) penetration of the electrode‐metals into the epitaxial layer. These phenomena are presumably caused by the abrupt passage of large current along the facet or by local heating at the contact region outside the stripe region. Catastrophic optical damage, which frequently occurs in GaAlAs/GaAs double‐heterostructure lasers, is not observed in any part of the degraded diodes.