Hideo Kashima

Tailored heterointerface formation in InGaAs/InP superlattices by gas source migration-enhanced epitaxy

Abstract InGaAs/InP short period superlattices (SPSLs) with different interface atomic arrangements were grown by gas source migration-enhanced epitaxy (GSMEE) on (001)InP substrates. The local structure found around interfaces was investigated by P K-edge X-ray absorption fine structure (XAFS) using synchrotron radiation (SR), and by highly sensitive Raman scattering spectroscopy. Persistent reflection high-energy electron diffraction (RHEED) oscillations reveal that layer-by-layer nucleation can take place even during the growth of heterointerfaces by precise control of migration-enhanced epitaxy (MEE) sequences. The RHEED intensity traces of InGaAs/InP SPSLs without special characteristic shapes at the heterointerfaces were observed for the first time. XAFS analysis shows that the first nearest neighbors to P in the sample with InGa-P interfaces are In and Ga and that the first nearest neighbor in the sample with In-As interfaces is In. No clear GaP longitudinal optical (LO) phonon line is observed in the Raman scattering spectrum for SPSL with In-As interfaces, while a sharp and strong GaP LO phonon line is detected in SPSL with InGa-P interfaces.

Effect of source-supply interruptions on the interface abruptness in gas source molecular beam epitaxy grown InGaAs/InP heterostructures

Abstract The effect of source-supply interruptions on the InGaAsInP heterointerface abruptness in gas-source molecular-beam epitaxy grown lattice-matched InGaAs/InP has been investigated. It is confirmed by observing high-resolution transmission electron microscope (HRTEM) images and photoluminescence (PL) peak energy shifts that the thickness of the InGaAs well becomes narrower as the source-supply interruption (SSI) becomes longer. When the SSI is not optimized, an interface layer forms, consisting of one to several strained monolayers as confirmed by PL and HRTEM. When the SSI is optimized, Auger electron microscopy, PL, and HRTEM reveal abrupt heterointerface formation.

Real‐time explosive particle detection using a cyclone particle concentrator

RATIONALE There is a need for more rapid methods for the detection of explosive particles. We have developed a novel real-time analysis technique for explosive particles that uses a cyclone particle concentrator. This technique can analyze sample surfaces for the presence of particles from explosives such as TNT and RDX within 3 s, which is much faster than is possible by conventional methods. METHODS Particles are detached from the sample surface with air jet pulses, and then introduced into a cyclone particle concentrator with a high pumping speed of about 80 L/min. A vaporizer placed at the bottom of the cyclone particle concentrator immediately converts the particles into a vapor. The vapor is then ionized in the atmospheric pressure chemical ionization (APCI) source of a linear ion trap mass spectrometer. RESULTS An online connection between the vaporizer and a mass spectrometer enables high-speed detection within a few seconds, compared with the conventional off-line heating method that takes more than 10 s to raise the temperature of a sample filter unit. Since the configuration enriched the number density of explosive particles by about 80 times compared with that without the concentrator, a sub-ng amount of TNT particles on a surface was detectable. CONCLUSIONS The detection limit of our technique is comparable with that of an explosives trace detector using ion mobility spectrometry. The technique will be beneficial for trace detection in security applications, because it detects explosive particles on the surface more speedily than conventional methods.

Dual-axis 360° rotation specimen holder for analysis of three-dimensional magnetic structures

A dual-axis 360° rotation specimen holder was developed for use in reconstructing the three-dimensional (3D) distribution of a magnetic field using a combination of electron holography and tomography. Pillar-shaped specimens are used to obtain accurate reconstruction without a missing angle. The holders rotation rod can be turned >360°; the pillar is set ±45° to the azimuth for both x- and y-axis rotation. Two rotation series of holograms in individual axes are recorded for vector field tomography. The two vector components of the magnetic field are reconstructed directly from the two series of holograms, and the remaining component is calculated using Maxwells equation, div B = 0. As a result, all 3D magnetic fields are reconstructed.

Gas source molecular beam epitaxy and X-ray absorption fine structure characterization of InGaAs/InP short period superlattices

Abstract InGaAs/InP short period superlattices (SPSLs) were grown using gas source migration enhanced epitaxy (GSMEE) and using gas source molecular beam epitaxy (GSMBE) on (001)InP substrates. The local structure around the interfaces was investigated by Ga K-edge X-ray absorption fine structure (XAFS) using synchrotron radiation (SR). It was confirmed by the observation of persistent reflection high-energy electron diffraction (RHEED) oscillations that layer-by-layer nucleation takes place even during the growth of the heterointerfaces by precise control of migration enhanced epitaxy (MEE) sequences. XAFS analysis showed that the first nearest neighbor around Ga in the GSMEE grown sample with In-As interfaces is As, while those in the GSMBE grown sample are As and P. These results suggest that the atomically-controlled abrupt heterointerfaces can be obtained by GSMEE, whereas some intermixing of atoms at the heterointerfaces takes place in samples grown by GSMBE.

Photoluminescence investigation of InGaAs/InP quantum wells grown by gas-source molecular-beam epitaxy with source-supply interruption

We present a detailed study of the effects of SSI on the interface configuration of lattice-matched InGaAs/InP heterostructures. Low-temperature photoluminescence (PL) analysis of InGaAs/InP quantum wells (QWs) with well thickness ranging from 1 to 16 nm was performed and the results were compared with theoretical calculations taking into account the transition layer at the heterointerface.

InP/InGaAs heterojunction bipolar transistors with regrown emitters

InP/InGaAs heterojunction bipolar transistors (HBTs) with regrown emitters for high-speed, low-power ICs have been fabricated with a newly developed structure. This is the first report of HBTs with regrown emitters as small as 2.5 /spl mu/m/spl times/2.5 /spl mu/m, small enough to be used in high-speed ICs, in this material system. Current gain of 24 was obtained with a 3.5 /spl mu/m/spl times/3.5 /spl mu/m emitter HBT. Short-range reliability of the regrown emitter HBTs was investigated for the first time. No degradation was observed in the current-voltage characteristics for 5000 sec under a collector current density as high as 1/spl times/10/sup 5/ A/cm/sup 2/.<<ETX>>