A. Utsumi

Dislocation-free GaAsyP1−x−yNx/GaP0.98N0.02 quantum-well structure lattice- matched to a Si substrate

We report that a lattice-matched and dislocation-free GaAsyP1−x−yNx/GaP0.98N0.02 quantum-well (QW) structure can be grown on a Si substrate. A two-dimensional growth mode was maintained during growth of all the layers. It was confirmed that the QW structure was lattice-matched to the Si substrate from the lattice constant measured by x-ray diffraction. A cross-sectional image taken by transmission electron microscopy revealed that no threading dislocations or misfit dislocations were observed at the QW structure.

Hardening Effect of GaP1-xNx and GaAs1-xNx Alloys by Adding Nitrogen Atoms

We investigated the strain relaxation process of GaP1-xNx/GaP and GaAs1-xNx/GaAs in order to clarify their mechanical characteristics by adding nitrogen atoms. It was observed by transmission electron microscopy (TEM) that the critical thicknesses were greater and the generation rates of the misfit dislocations were slower in the GaP1-xNx and GaAs1-xNx layers than those in the GaP layer with a similar lattice mismatch. The critical thickness of the GaAs1-xNx layer was greater than that of the GaP1-xNx layer for the same nitrogen composition of 2%. The direction of higher crack density was orthogonal to that of the higher misfit dislocation density. These results indicate that the propagation of dislocations is prevented in III–V–N alloys such as GaP1-xNx and GaAs1-xNx, so that these alloys are harder than III–V compounds that lack nitrogen atoms. This feature could be attributed to the dislocation pinning and alloy hardening effects due to nitrogen atoms.

Formation of grown-in defects in molecular beam epitaxial Ga(In)NP: Effects of growth conditions and postgrowth treatments

Effects of growth conditions and post-growth treatments, such as presence of N ions, N2 flow, growth temperature, In alloying, and postgrowth rapid thermal annealing (RTA), on formation of grown-in defects in Ga(In)NP prepared by molecular beam epitaxy are studied in detail by the optically detected magnetic resonance (ODMR) technique. Several common residual defects, such as two Ga-interstitial defects (i.e., Gai-A and Gai-B) and two unidentified defects with a g factor around 2 (denoted by S1 and S2), are closely monitored. Bombardment of impinging N ions on grown sample surface is found to facilitate formation of these defects. Higher N2 flow is shown to have an even more profound effect than a higher number of ions in introducing these defects. Incorporation of a small amount of In (e.g., 5.1%) in GaNP seems to play a minor role in the formation of the defects. In GaInNP with 45% of In; however, the defects were found to be abundant. Effect of RTA on the defects is found to depend on initial configura...

Control of growth process and dislocation generation of GaAs1−xNx grown by all-solid-source molecular beam epitaxy

We investigated the growth process and dislocation generation of GaAs 1-x N x alloys grown on GaAs by solid-source molecular beam epitaxy (MBE). It was found that the GaAs 1-x N x alloys with a mirror-like surface can be grown by lowering the arsenic-to-gallium flux ratio compared to that in the growth of GaAs. The nitrogen composition in the GaAs 1-x N x alloys increased with decreasing substrate temperature and with increasing RF-power. As the nitrogen composition increased, the misfit dislocations were observed at the GaAs 1-x N x -GaAs heterointerface. It was clarified that the propagation of dislocations was suppressed in GaAs 1-x N x alloys by adding nitrogen.

Effect of nitrogen ion bombardment on defect formation and luminescence efficiency of GaNP epilayers grown by molecular-beam epitaxy

Radiative efficiency of GaNP epilayers grown on GaP substrates by solid-source molecular beam epitaxy is significantly improved by reduced nitrogen ion bombardment during the growth. Based on the results of temperature-dependent photoluminescence (PL) and optically detected magnetic resonance studies (ODMR), the observed improvements are attributed to reduced formation of defects, such as a Ga interstitial related defect and an unidentified defect revealed by ODMR. We demonstrate that these defects act as competing recombination centers, which promote thermal quenching of the PL intensity and result in a substantial (34×) decrease in room-temperature PL intensity.

Effects of rapid thermal annealing on optical properties of GaNxP1−x alloys grown by solid source molecular beam epitaxy

Temperature-dependent photoluminescence (PL), PL excitation and time-resolved PL measurements were employed to study the effects of rapid thermal annealing (RTA) on optical properties of GaNxP1−x alloys grown by solid source molecular beam epitaxy. A substantial increase in radiative efficiency of GaNP epilayers, which is especially pronounced for the high-energy PL component, was achieved after RTA and is attributed to annealing out of competing non-radiative centres. The latter is evident from reduced quenching of the PL intensity with increasing measurement temperature, which results in a strong increase (up to 18 times) in the PL intensity at room temperature (RT), as well as from a substantial increase in carrier lifetime at RT deduced from time-resolved PL measurements.

Evaluation of optical quality and defect properties of GaNxP1−x alloys lattice matched to Si

By using a variety of optical characterization techniques, including cathodoluminescence, temperature-dependent cw- and time-resolved photoluminescence (PL), and PL excitation spectroscopies, high ...

Improvement of crystalline quality of GaAsyP1−x−yNx layers with high nitrogen compositions at low-temperature growth by atomic hydrogen irradiation

Abstract We proposed a growth technique for III–V–N alloys with high quality and nitrogen composition, which was the low-temperature growth under atomic hydrogen irradiation. In the growth of GaPN, nitrogen compositions higher than 6% were obtained at growth temperatures lower than 350°C. GaAsPN alloys grown on GaP substrates were examined using X-ray diffraction and transmission electron microscopy. It was found that structural crystalline quality of a GaAs y P 0.93− y N 0.07 layer grown at 350°C was improved by atomic hydrogen irradiation. Photoluminescence was obtained from a GaAs 0.33 P 0.60 N 0.07 /GaP double heterostructure lattice matched to a GaP substrate.

Performance of Random Metal-Dielectric Film on Optical Signal Transmissions

The transmission performances of a random metal-dielectric film composed of silver metal and spherical fused silica balls were experimentally investigated for intensity- and frequency-modulated optical signals. The film was formed on the facet of a laser diode, and intensity-modulated optical signals emitted from the laser diode were successfully transmitted through it. Frequency-modulation optical signals were successfully detected by using an optical heterodyne technique. These results indicate that this random metal-dielectric film is well suited for use as a waveguide for optical signal transmission.

The operating characteristics of an optical near-field generator fabricated on laser diodes

The operating characteristics of a novel optical near-field generator are described in detail. The generator was fabricated by forming a random metal-dielectric film composed of silver paste and spherical fused silica on the facet of a laser diode. The relationship between the current injected to the laser diode and the intensity of the optical near field is similar to that between the injected current and optical output power emitted from the opposite facet having no metal-dielectric film, although the magnitude of the optical intensity is very different. The threshold current and kink-points in the current-optical intensity relation show no difference in the both relationships. Lasing spectra observed in propagating light scattered from the optical near field corresponds to those of light emitted from the opposite facet. The direct current (DC) characteristics of the optical near field are similar to those of the propagating light emitted from the laser diode, and the linear relationship is maintained between DC characteristics of the optical near field and of the propagating light. The modulation characteristics of the optical near-field coincide with those of laser diodes because the intensity of the optical near field linearly responds to the magnitude of the injected current of the laser diode. These results confirm that the optical near-field generator is a practical optical source and will be important for future photonic devices such as OEICs.