Jun Tatebayashi

Over 1.5 μm light emission from InAs quantum dots embedded in InGaAs strain-reducing layer grown by metalorganic chemical vapor deposition

We demonstrated the 1.52 μm light emission at room temperature from self-assembled InAs quantum dots embedded in the In0.45Ga0.55As strain-reducing layer. By capping InAs quantum dots with an InGaAs strain-reducing layer instead of GaAs, the photoluminescence peak of InAs quantum dots can be controlled by changing the indium composition of the InGaAs strain-reducing layer. The full width at half maximum is as narrow as 22 meV. The wavelength of 1.52 μm is the longest wavelength so far achieved in self-assembled InAs quantum dots, which would be promising to quantum-dot lasers on GaAs substrate for application to light sources in long-wavelength optical communication systems.

1.28μm lasing from stacked InAs∕GaAs quantum dots with low-temperature-grown AlGaAs cladding layer by metalorganic chemical vapor deposition

We report the device characteristics of stacked InAs∕GaAs quantum-dot lasers cladded by Al0.4Ga0.6As layer grown at a low temperature by metalorganic chemical vapor deposition. A blueshift in emission energy by the effect of postgrowth annealing can be suppressed when the annealing temperature is below 570°C. We achieved the 1.28μm continuous-wave lasing at room temperature of five layer stacked InAs∕GaAs quantum dots embedded in In0.13Ga0.87As strain-reducing layer whose p-cladding layer is grown at 560°C. From the experiments and calculations of the gain spectra of fabricated quantum-dot lasers, the observed lasing originates from the first excited state of stacked InAs quantum dots.

Area-controlled growth of InAs quantum dots and improvement of density and size distribution

We propose and demonstrate a scheme (area-controlled growth) for controlling where self-assembled InAs quantum dots form, using a SiO2 mask and selective area metalorganic chemical vapor deposition growth. Using this technique, quantum dots can be formed in only selected areas of a growth plane. However, in the regions where dots are formed there is variation of dot density and size along the mask stripe direction because of the diffusion of species in the vapor phase. We achieve more uniform distributions of dot density and size by changing the mask pattern. Using this growth technique, it is possible to fabricate integrated optical devices containing an external reflector together with quantum dots serving as the active layer of a semiconductor laser.

InAs∕GaAs self-assembled quantum-dot lasers grown by metalorganic chemical vapor deposition—Effects of postgrowth annealing on stacked InAs quantum dots

We investigated the effects of postgrowth annealing on stacked InAs∕GaAs quantum dots. The blueshift in emission energy by postgrowth annealing depends on the temperature of postgrowth annealing and the growth conditions of stacked InAs quantum dots, such as a spacer thickness or a stacking number. We can control the peak wavelength of stacked InAs quantum dots by changing the temperature of postgrowth annealing and the growth conditions of stacked InAs quantum dots. We achieved continuous-wave lasing with a threshold current of 16.4mA at the wavelength of 1.245μm from five layer vertically aligned InAs quantum dots whose upper cladding layer was grown at 600°C.

Control of optical polarization anisotropy in edge emitting luminescence of InAs/GaAs self-assembled quantum dots

We have studied the polarization properties of cleaved-edge photoluminescence (PL) from InAs/GaAs self-assembled quantum dots. Transverse-electric (TE) and transverse-magnetic (TM) mode PL intensities have been analyzed for the dots having 8 nm InxGa1−xAs capping layer with indium (In) composition of x=0 and 0.13. Polarization results show a dramatic change with the capping layer In compositions; TE-mode dominant PL is observed for dots with x=0, on the other hand, TM-mode dominant PL for dots with x=0.13. This polarization change has been attributed to the dot shape change using transmission electron microscopy images. These results suggest that the optical polarization anisotropy of the quantum dots can be controlled by manipulating the capping layer In composition.

Narrow photoluminescence linewidth (<17 meV) from highly uniform self-assembled InAs/GaAs quantum dots grown by low-pressure metalorganic chemical vapor deposition

We report highly uniform self-assembled InAs quantum dots (QDs) emitting at 1.3 μm, grown on GaAs substrates by low-pressure metalorganic chemical vapor deposition. By optimizing the InAs growth rate and capping the QDs with GaAs using triethylgallium as a gallium source, we have achieved a narrow photoluminescence (PL) inhomogeneous linewidth of 16.5 meV (at 7 K) from QDs with a density of 1.7×1010 cm−2. Furthermore, we show by temperature-dependent PL measurements that the QDs exhibit almost no dependence of linewidth on temperature due to their high uniformity.

Lasing characteristics of InAs quantum-dot microdisk from 3 K to room temperature

We fabricated a microdisk laser with five-stacked InAs quantum-dot (QD) active region, and demonstrated the lasing operation from 3K to room temperature by femtosecond pulsed photopumping. At room temperature, the threshold power was estimated to be 0.75mW, when the influence of the surface recombination at the disk edge was neglected. The lasing wavelength was 1.2–1.3μm, which corresponded to excited states of the QDs. The temperature dependence of the threshold, slope efficiency, lasing wavelength, and linewidth are explained by the rapid increase in nonradiative recombination and internal absorption at critical temperatures of 200–230K.

Effects of rapid thermal annealing on the emission properties of highly uniform self-assembled InAs∕GaAs quantum dots emitting at 1.3μm

The authors report the effects of rapid thermal annealing (RTA) on the emission properties of highly uniform self-assembled InAs quantum dots (QDs) emitting at 1.3μm grown on GaAs substrate by metal organic chemical vapor deposition. Postgrowth RTA experiments were performed under N2 flow at temperatures ranging from 600to900°C for 30s using GaAs proximity capping. Surprisingly, in spite of the capping, large blueshifts in the emission peak (up to about 380meV at 850°C) were observed (even at low annealing temperatures) along with enhanced integrated photoluminescence (PL) intensities. Moreover, pronounced peak broadenings occurred at low annealing temperatures (<700°C), indicating that RTA does not always cause peak narrowing, as is typically observed with traditional QDs with large inhomogeneous PL linewidths. The mechanism behind the large peak blueshift was studied and found to be attributed to the as-grown QDs with large size, which cause a larger dot-barrier interface and greater strain in and near ...

Improvement of the uniformity of self-assembled InAs quantum dots grown on InGaAs∕GaAs by low-pressure metalorganic chemical vapor deposition

We report an approach to improve the uniformity of self-assembled InAs quantum dots (QDs) grown on a strained In0.12Ga0.88As buffer layer on GaAs substrates by low-pressure metalorganic chemical vapor deposition. By inserting a thin GaAs layer between the InAs QD layer and the In0.12Ga0.88As buffer layer and examining its thickness effect, we demonstrate that the photoluminescence (PL) inhomogeneous linewidth from the QDs can be improved by increasing the thickness of the thin GaAs layer. The PL inhomogeneous linewidth is significantly decreased from about 70to20meV at 7K as the thickness is increased from 0to2nm. This significant improvement of the PL inhomogeneous linewidth is due to the fact that the QDs change from a bimodal distribution to a monomodal distribution consisting only of large QDs as a result of the inserted thin GaAs layer.

Lasing at 1.28 /spl mu/m of InAs-GaAs quantum dots with AlGaAs cladding layer grown by metal-organic chemical vapor deposition

We report the device characteristics of stacked InAs-GaAs quantum dot (QD) lasers cladded by an Al/sub 0.4/Ga/sub 0.6/As layer grown at low temperature by metal-organic chemical vapor deposition. In the growth of quantum dot lasers, an emission wavelength shifts toward a shorter value due to the effect of postgrowth annealing on quantum dots. This blueshift can be suppressed when the annealing temperature is below 570/spl deg/C. We achieved 1.28-/spl mu/m continuous-wave lasing at room temperature of five layers stacked InAs-GaAs quantum dots embedded in an In/sub 0.13/Ga/sub 0.87/As strain-reducing layer whose p-cladding layer was grown at 560/spl deg/C. From the experiments and calculations of the gain spectra of fabricated quantum dot lasers, the observed lasing originates from the first excited state of stacked InAs quantum dots. We also discuss the device characteristics of fabricated quantum dot lasers at various growth temperatures of the p-cladding layer.