Yasutaka Matsui

Sb surfactant effect on GaInAs/GaAs highly strained quantum well lasers emitting at 1200 nm range grown by molecular beam epitaxy

A surfactant effect of antimony (Sb) on highly strained GaInAs quantum wells (QWs) was studied by molecular beam epitaxy. Noticeable improvement of the photoluminescence (PL) was observed by adding the dilute Sb. The QWs showed an increased PL intensity and narrow linewidth of 23 meV for the wavelength range up to 1180 nm. An atomic force microscope study showed a flattened surface morphology by the introduction of the Sb. Broad-area lasers with a GaInAsSb/GaAs double-QW active layer emitting at 1170 nm showed a low threshold current density of 125 A/cm2 per well for an infinite cavity length.

Surfactant effect of Sb on GaInAs quantum dots grown by molecular beam epitaxy

A surfactant effect of antimony (Sb) was investigated for self-assembled GaInAs quantum dots (QDs). The introduction of Sb into the QDs cause a large blue shift of the photoluminescence (PL) wavelength with a decrease in the full width at half maximum (FWHM) and an increase in intensity in comparison with QDs without Sb. Atomic force microscope (AFM) measurement showed a marked reduction in QD density from 1.0×1010 cm-2 to 7.0×107 cm-2. This indicates that Sb suppresses the formation of QDs and that the wetting layer remains to be a quantum well (QW) structure. The PL wavelength of the GaInAsSb wetting layer was elongated by increasing the amount of Sb supply. This result indicates the expansion of the critical thickness of the growth mode change from 2D to 3D.

p-Type Doping Characteristics of GaInNAs:Be Grown by Solid Source Molecular Beam Epitaxy

We investigated the doping and electrical characteristics of p-type GaInNAs for use in a p-contact layer and in the p-distributed Bragg reflectors ( p-DBRs) of surface emitting lasers. Beryllium doping was applied to GaInNAs grown by solid source molecular beam epitaxy with the nitrogen radical. The doping efficiency for the lattice-matched GaInNAs is similar to that of the GaAs, and a slight deterioration in hole mobility indicates the alloy scattering of the GaInNAs.

Elongation of emission wavelength of GaInAsSb-covered (Ga)InAs quantum dots grown by molecular beam epitaxy

We demonstrated the elongation of the photoluminescence wavelength of (Ga)InAs quantum dots (QDs) using a highly strained the GaInAsSb cover layer for the first time. The effect of a GaInAsSb cover layer on the optical properties of (Ga)InAs self-organized QDs was investigated for various In compositions in dots and cover layers. The emission wavelength of (Ga)InAs QDs can be elongated by increasing the indium composition of the GaInAsSb cover layer while maintaining the optical quality of QDs. The result would be promising for QD lasers on a GaAs substrate for use in long-wavelength fiber optical communications.

Optical Quality Dependence on Growth Rate for Solid-Source Molecular Beam Epitaxy Grown Highly Strained GaInAsSb/GaAs Quantum Wells

The optical quality dependence on the growth rate for Sb-introduced highly strained GaInAs quantum wells (QWs) was studied by solid-source molecular beam epitaxy (MBE). Noticeable improvements in the photoluminescence (PL) were observed upon lowering the growth rate, even for a highly strained material. Under an optimized Sb flux for each growth rate, a sample grown at the low growth rate of 0.09 µm/h showed a higher PL intensity than other samples grown at 0.17–0.57 µm/h. These samples showed a flat surface in atomic force microscope (AFM) measurements, while Sb-free GaInAs QWs showed no PL emission and quite a rough surface caused by the three dimensional growth typically observed in a highly strained material grown at a low growth rate. It was found that a low growth rate is effective for improving the optical characteristics of highly strained GaInAs QWs in the case of Sb introduction.

Wavelength elongation of MBE grown (Ga)InAs QDs by GaInAsSb cover layer

We demonstrated the elongation of the photoluminescence (PL) wavelength of (Ga)InAs quantum dots (QDs) using a highly strained GaInAsSb cover layer for the first time. The effect of the GaInAsSb cover layer on the optical properties of (Ga)InAs self-organized QDs was investigated for various indium (In) compositions in dots and cover layers. The emission wavelength of (Ga)InAs QDs was elongated by increasing the In composition of the GaInAsSb cover layer up to 1.38 /spl mu/m for GaInAs QDs and up to 1.48 /spl mu/m for InAs QDs while maintaining the emission efficiency. The result would be promising for QD lasers on a GaAs for use in long-wavelength fiber optical communications.

Structure dependence of lasing characteristics of GaInAs/AlGaAs tunnel injection lasers

Lasing characteristics of MBE grown GaInAs/AlGaAs single QW lasers with double barrier tunnel injection structures are investigated. The I-L characteristics are strongly affected by the tunnel injection structure. A high characteristic temperature of 164K is obtained.

Investigation of well thickness reduction effect of GaInNAs/GaAs quantum well lasers

We investigated the advantageous of a thin quantum well (QW) for GaInNAs laser performances. We pointed out that the reduction of the well thickness has almost no disadvantage on the optical gain and the carrier overflow due to a large conduction band offset. A thin QW is advantageous for suppression of the carrier overflow to the higher quantized energy levels which results In good temperature and gain characteristics. A thin GaInNAs QW is a good candidate for an active layer structure of the laser utilized in high performance optical communication systems.

Thermal annealing effect on self-assembled GaInNAs/GaAs quantum dots grown by chemical beam epitaxy

The self-assembled GaInNAs quantum dot (QD) has proposed as a novel material system for long wavelength lasers on GaAs substrate. In this paper, we have investigated the thermal annealing effect on GaInNAs QDs. The increase of the PL intensity and blue shift of peak wavelength was observed by thermal annealing. For 600/spl deg/C annealing, the PL intensity was increased with the increase of annealing time and maximum intensity was obtained at 2 hours. On the other hand, PL intensity was increased after 30s annealing, then decreased at longer time for 700/spl deg/C annealing. A larger blue shift of peak wavelength compared to GaInNAs quantum well was observed. It is considered that the interdiffusion was enhanced in QD system due to its large strain and interface area between GaAs capping layer.