Kikuo Kobayashi

Si doping and MBE growth of GaAs on tilted (111)A substrates

Abstract Molecular beam epitaxy of GaAs doped with Si on a vicinal surface of (111)A, (211)A and (311)A have been examined. The variations of the impurity concentrations are dependent on the growth conditions and are affected by the angle of the substrates. The impurity concentrations are compared with a model calculation which is based on microscopic surface structures and kinematical surface reactions. Growth modes are monitored by reflection high-energy electron diffraction intensity oscillations. A doping mechanism of Si atoms into GaAs films is proposed.

Blue luminescent SrGa2S4:Ce thin films grown by molecular beam epitaxy

Abstract SrGa 2 S 4 polycrystalline thin films, currently attracing much attention as host material for blue electroluminescence, are grown by MBE employing Sr metal and Ga 2 S 3 compound as source materials. The stoichiometry of this film can be controlled by changing the Ga 2 S 3 /Sr flux ratio. A single-phase SrGa 2 S 4 layer with high crystallinity is obtained in a flux ratio of 60 at the growth temperature of 560°C. A Ce-doped SrGa 2 S 4 phosphor film shows efficient blue photoluminescence (PL) whose chromaticity is comparable to that of blue CRT phosphors.

Lateral p-n junctions on GaAs(111)A substrates patterned with equilateral triangles

Abstract We report the successful formation of lateral p-n junctions by molecular beam epitaxy (MBE) of Si-doped GaAs on (111)A substrates patterned with equilateral triangles. The idea of lateral p-n junctions with a triangular p-type region encircled with three crystallographically equivalent n-type slopes is based on the three-fold symmetry of the (111)A surface and the acceptor nature of the dopant Si on the (111)A surface in contrast to the donor nature on surfaces with the other orientations. Bad surface morphologies of layers grown on the (111)A surface have been a barrier against practical applications of this surface. We have successfully improved the (111)A surface morphology by pre-growth thermal cleaning, at both higher temperatures and higher As pressures. The formation of lateral p-n junctions is confirmed by spatially resolved cathodoluminescence measurements. This lateral p-n junction can be applied to structures that demand lateral carrier confinement, such as surface emitting laser diodes.

Dependence on Ce Concentration of Blue Emission and Crystallographic Properties in SrGa2S4:Ce Electroluminescent Thin Films Grown by Molecular Beam Epitaxy

The Ce-doping dependence of blue emission properties has been investigated for SrGa2S4:Ce electroluminescent (EL) thin films grown by molecular beam epitaxy (MBE). EL spectra, EL luminance, photoluminescence (PL) spectra, X-ray diffraction (XRD) intensity, XRD rocking curves, spacing of lattice planes, EL and PL decay times were measured in samples with Ce-doping concentrations ranging from 0.87 mol% to 8.37 mol%. EL luminance reached a maximum at 2.40 mol%. In particular, EL chromaticity remained within the pure blue region even with higher Ce-doping concentrations.

Increase in Uniformity of Amorphous GdCo Films by Control of Oxygen Quantity

The spatial uniformity of compositions and of the magnetic property of rf-sputtered amorphous GdCo thin films was investigated by Auger electron spectroscopy, electron probe microanalyzer, and polar Kerr hysteresis loops. It was found that by applying a negative dc bias to the substrate during sputtering, the quantity of oxygen incorporated into the film decreases and considerable uniformity of the oxygen and of magnetic property is obtained, though the magnetic property shows a slight increase in compensation temperature toward the edge. This slight change was found to come from a change in composition of the metals. A further increase in uniformity was achieved by intentionally introducing a small amount of oxygen during the deposition process.

Electrical Characterization of Lateral P-N Junctions Grown on (111)A GaAs Nonplanar Substrates by Molecular Beam Epitaxy

Electrical characteristics of lateral p-n junctions grown on (111)A GaAs nonplanar substrates by molecular beam epitaxy are investigated. According to current-voltage and capacitance-voltage measurements, it is clarified that uniformly Si-doped lateral p-n junctions have graded doping profiles at the intersection between the (111)A flat plane and (311)A side slope, and the lateral p-n interface becomes steeper with decreasing growth temperature. In the δ-doped lateral p-n junction, negative resistance is observed in the current-voltage characteristics. Assuming it is due to interband tunneling, we consider that the δ-doped lateral p-n junction has a steeper interface than the uniformly doped lateral p-n junctions. These junction characteristics are discussed in relation to the surface migration of Ga adatoms.

Influence of Oxygen on the Uniformity of RF-Sputtered Amorphous GdCo Films

The spatial uniformity of rf-sputtered amorphous GdCo films has been investigated by electron probe microanalyzer. It has been found that the concentration of oxygen increases from the center of the film toward the edge, while the concentration of metals is constant throughout the film. Study by the polar Kerr effect has revealed that the compensation temperature of the film is lower at the edge than at the center. From these results we conclude that the non-uniformity of the magnetic property of our films arises mainly from the non-uniformity of the oxygen distribution.

MBE growth of GaAs p-n junction LEDs on (111)A GaAs substrates using only silicon dopant

GaAs LEDs were fabricated on (111)A GaAs substrates using a p-n structure grown with controlled all-Si doping. Cathodoluminescence spectra and I–V characteristics for these samples confirmed p-n structures. The peak intensity of the samples emission spectrum was equivalent to that of the sample grown using Be as the p-type dopant. As the forward current was increased, the intensity increased without a peak shift, which was observed in the Be-doped sample. A SIMS study of Si or Be diffusion in the p-type layer using a delta-doped GaAs layer suggests that the peak shift is caused by Be diffusion.

Periodic lateral structure of Al content modulations in AlGaAs grown on vicinal (111)A GaAs by molecular beam epitaxy

Abstract The photoluminescence spectra of single quantum well (SQW) structures grown on (111)A GaAs misoriented 3° towards the [100] direction are red shifted and broadened. These spectra also have extra peaks on the high-energy side, and the surface of the SQWs show giant steps towards [110] and [101] direction. Cross-sectional transmission electron microscopy of the SQWs on the 3°-misoriented (111)A surface clearly shows that the Al content is lower in the AlGaAs regions parallel to the (221)A or (331)A orientation and that the widths of GaAs wells increases at the risers of the giant steps towards [110] and [101]. On the exactly (111)A surfaces, the peak cathodoluminescence wavelength shows that the Al content on the AlGaAs triangle facets consisting of (221)A or (331)A planes is lower than on the flat surfaces. The AlGaAs layers grown on (111)A GaAs misoriented toward [011] have photoluminescence spectra whose intensity is stronger, and whose line width is narrower than the spectra from the AlGaAs layers grown on (111)A GaAs misoriented toward [100]. These phenomena are especially active for the AlGaAs grown on (111)A GaAs misoriented toward [110]. These novel lateral structures are most likely caused by the different sticking coefficients of Ga adatoms between on (111)A surfaces and (110) surfaces.

Transmission Self-Electro-Optic Effect Devices Based on Wannier-Stark Localization in a GaAs/AlAs Superlattice

We have studied optical switching of transmission-type self-electro-optic effect devices (SEEDs) based on Wannier-Stark localization (WSL) in a GaAs/AlAs superlattice (SL). Switching properties of both resister-biased and symmetric SEED are investigated as a function of operation wavelength. Clear optical bistability between two stable transmission states is obtained in the S-SEED configuration using the WSL. The detailed results of optical switching experiments are presented and explained in terms of a blue-shift mechanism of the optical absorption edge and an additional absorption mechanism due to spatially indirect Stark-ladder transitions in the SL. The SEED operation with a high transmission state is also demonstrated, and the advantages of the WSL are discussed for application to vertical transmission photonic switches.