Hidenao Tanaka

METALORGANIC VAPOR-PHASE EPITAXY OF CUBIC ALXGA1-XN ALLOY ON A GAAS (100) SUBSTRATE

Cubic AlxGa1−xN was grown on a GaAs (100) substrate by using low-pressure metalorganic vapor-phase epitaxy with a GaN buffer layer grown at low and high temperatures. The high-growth–temperature GaN layer improved the quality of the cubic AlxGa1−xN. Also, the AlN molar fraction could be controlled by changing the carrier gas flow of trimethylaluminum. The AlxGa1−xN epitaxial layers in the range of 0⩽x⩽0.23 exhibited strong near-band-edge photoluminescence at room temperature. Their photoluminescence peak energies show a linear dependence on the molar fraction.

Stimulated emission at 34 K from an optically pumped cubic GaN/AlGaN heterostructure grown by metalorganic vapor-phase epitaxy

A cubic GaN/AlGaN heterostructure has been grown on a GaAs (100) substrate by metalorganic vapor-phase epitaxy under low V/III ratio conditions, which resulted in a flat GaN layer. Stimulated emission was observed at 387 nm from the cleaved edge of an optically pumped cubic GaN/AlGaN heterostructure at 34 K. The threshold power density was 2.4 MW/cm2.

52.3: Direct‐viewing Display Using Alignment‐controlled PDLC and Holographic PDLC

A novel direct-viewing display using illumination from guided light is proposed. By analyzing usual normally scattering PDLC, we found that use of high-speed alignment-controlled PDLC combined with a field-sequential color technique is promising for full-color moving-picture displays. Moreover, introducing a holographic structure improves the contrast and viewing angle characteristics.

Metalorganic Vapor-Phase Epitaxial Growth and Characterization of Cubic AlxGa1-xN Alloy

Cubic AlxGa1-xN alloy films in the range 0≤x≤0.51 were grown on GaAs (100) substrates using low-pressure metalorganic vapor-phase epitaxy. The lattice constants of the alloys, which were estimated from the X-ray diffraction peaks, obeyed Vegards rule. The optical quality of the alloys was improved by using triethylaluminum as the aluminum precursor. In photoluminescence measurements, AlxGa1-xN in the range x≤0.42 exhibited strong near band edge emissions, while that with x around 0.5 did not. The peak energy of the photoluminescence depended on the relationship E=3.20+1.85x in the range x≤0.42, while that around x=0.5 was less than that given by this relationship.

Etching of cubic GaN by annealing in hydrogen ambient

Cubic GaN was annealed in different ambient gases at various temperatures from 800 to 950°C. It remained stable in inert gases, but it sublimated in hydrogen ambient. This sublimation was suppressed in H 2 + NH 3 and H 2 + TEGa mixtures. The sublimation rate in H 2 can be controlled by changing the annealing temperature: the activation energy of the sublimation was estimated to be 37 kcal/mol. Observation of the anisotropic properties at the cross section of a stripe etched by this sublimation showed that (111)B surfaces were stabilized during the etching. To estimate the damage during etching, we measured the photoluminescence from etched and rested surfaces. There was no difference in the shape of the spectrum, and the decrease in intensity with etching was only 18% when the film thickness was reduced by 15%.

Optically pumped stimulated emission from cubic GaN/AlGaN double heterostructure grown on GaAs(1 0 0) using metalorganic vapor-phase epitaxy

A cubic GaN/AlGaN double heterostructure has been grown on a GaAs(1 0 0) substrate by metalorganic vapor-phase epitaxy under low V/III ratio conditions, resulting in a flat GaN layer. Stimulated emission was observed at 387 nm from a cleaved edge of an optically pumped cubic GaN/AlGaN double heterostructure at 34 K. The threshold power density was 1.1 MW/cm 2 , which is lower than that of a single heterostructure device.

AFM measurement of initially grown GaN layer on GaAs substrate

We measured the surface roughness of initially grown GaN layers on GaAs substrates in different precursor supply conditions. The surface morphology changed dramatically at low precursor flow even though the V/III ratio was constant. At low supersaturation, the number of grains decreased and the grain size enlarged. Therefore the surface was too rough to cover the GaAs substrate. A stepping-stone-like morphology occurred in extreme cases. A few cores grew abnormally large grains. Only nitridation occurred when supersaturation was too low to grow a GaN core. To cover the GaAs surface with a thin GaN layer, a fairly large precursor supply was necessary.

Dependence of Viewing Characteristics on Polarization of Scattered Light from PDLC Illuminated by Planar Light Guide

Abstract The viewing characteristics of normally scattering polymer dispersed liquid crystal (PDLC) illuminated by guided light were studied. Luminance inversion occurred at viewing angles of more than 40° for the polarization component parallel to the plane of incidence, while the contrast ratio was more than 1 at all angles for the polarization component perpendicular to that plane. The luminance inversion was caused by the refractive index mismatch for the polarization component parallel to the plane of incidence even when an electric field was applied. By controlling the polarization of scattered light, we could suppress the luminance inversion.