-
[show abstract]
[hide abstract]
ABSTRACT: An ultrahigh vacuum scanning tunneling microscope (STM) with a new piezo‐driven inchworm for coarse positioning has been designed and constructed. The inchworm consists of five piezoelectric stacks and moves, being pressed from the side by a spring. This structure makes it durable to bakeout of the vacuum chamber. The tip and the sample set in the tunneling unit are exchangable without breaking vacuum. The STM chamber is attached to a conventional molecular beam epitaxy chamber equipped with surface analysis instruments without external vibration isolation. We have ascertained that the STM has an atomic‐order resolution even under poor conditions, where much acoustic noise and mechanical vibration are produced by vacuum pumps and cooling water in the main chamber.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 02/1990; · 1.25 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have studied interfacial atomic steps in GaAs/AlAs superlattices using high‐resolution transmission electron microscopy (HRTEM) and lattice image simulation. We find arrays of bright spots at the interface in the TEM image to be good indicators of the interface configuration. Doubling of the bright spot arrays and step‐shaped arrays in TEM lattice images indicate a ‘‘type 1’’ monolayer step whose front is perpendicular to the direction of the electron beam and a ‘‘type 2’’ monolayer step whose front is parallel to the direction of the electron beam. Our HRTEM observations indicate that the atomic steps at GaAs and AlAs interfaces grown at 700 °C are denser than at interfaces grown at 500 °C.
Applied Physics Letters 09/1988; · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A small angle X-ray diffraction using synchrotron radiation, microscopic Raman spectroscopy and a high-resolution TEM were used to characterize superlattices (SLs) grown at 500, 600, and 700°C. The periodicity of the SLs was not degraded, but transition-layer thickness increased with the growth temperature. The transition layer was revealed to be atomic-layer steps with a monolayer per length >100 A for the 500°C-, and with one or two monolayers per length less than 30 A for the 700°C-grown SLs.
Le Journal de Physique Colloques 01/1987; 48(C5):41.
-
[show abstract]
[hide abstract]
ABSTRACT: We fabricated and life‐tested visible AlGaAs/GaAs channeled‐substrate‐planar‐type lasers and found that some are degraded within 100 h of operation. We investigated these using photoluminescence and transmission electron microscopic images. The characteristic features in photoluminescence images are dark defects that run parallel to the channeled stripe. Using transmission electron microscopy, we found that these dark defects are composed of precipitates, dislocation loops, and dislocation dipoles. In order to know the relation between these degradation phenomena and the thermal strain induced by lattice mismatch, we calculated the stress distribution in the semiconductor laser using the finite element method. According to this simulation, a stress concentration in the active layer arises near the edges of the channeled stripe where the volume dilatation is maximal. Combining the results of experiments and simulation, we concluded that interstitial atoms created by nonradiative recombination migrate to the edges of the stripe, and that ultimately dark defects appear near the edges of the stripe.
Journal of Applied Physics 11/1985; · 2.17 Impact Factor
-
IEEE Transactions on Electron Devices 11/1982; · 2.32 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The cross-sectional shape of LPE InGaAsP layers in a V-groove on InP substrates has been studied experimentally and theoretically. The shape varies from an arc to a V-shape as the composition goes away from InP. We have shown that this phenomenon can be explained by calculating the free energy. Calculation shows that the shape of the grown layer in the V-groove is determined by the contact angle between its surface and the facet of the groove.
Journal of Crystal Growth 69(1):161-164. · 1.73 Impact Factor
