Takeru Amano

Design and fabrication of GaAs-GaAlAs micromachined tunable filter with thermal strain control

In this paper, we present the design and fabrication of a novel GaAlAs-GaAs micromachined vertical cavity filter with a thermal strain control layer for wide wavelength tuning. The integration of a thermal strain control layer and heating element enables wavelength tuning induced by heating. The proposed tunable filter under thermal tuning operation provides us large tuning range over conventional micromachined tunable filters using electrostatic force. The calculated result shows a possibility of large continuous tuning range of over 100 nm. We fabricated a micromachined GaAlAs-GaAs vertical cavity filter with a strain control layer. The temperature dependence of the filter can be freely controlled either with temperature insensitive operation or with an enhanced temperature dependence, which depends on the thickness of the thermal strain control layer. We demonstrate a thermal wavelength tuning of 53 nm with a low tuning voltage of 6.1 V for the first time.

Highest Density 1.3 µm InAs Quantum Dots Covered with Gradient Composition InGaAs Strain Reduced Layer Grown with an As2 Source Using Molecular Beam Epitaxy

We propose a GaAs-based 1.3 µm InAs quantum dot (QD) structure for optical devices that uses dimeric arsenic (As2) and a highly strained GaInAs cover layer. The characteristics of 1.3 µm InAs QDs that employ As2 are different from those of QDs that use As4. Our optimum structure exhibits the first room temperature emission of over 1.3 µm with a linewidth of 22 meV and a high density of over 1 ×1011 cm-2 using only a cover layer. We were also able to achieve a very high density of 3.3 ×1011 cm-2 and a full width at half mazimum of 23 meV for a triple-stack structure within the critical thickness. This result is promising as regards achieving an optical device with QDs of over 1.3 µm on a GaAs substrate for use in fiber communications.

Temperature-insensitive micromachined AlGaAs-GaAs vertical cavity filter

We have demonstrated a temperature-insensitive micromachined vertical cavity filter with an AlGaAs-GaAs distributed Bragg reflector (DBR), which can be thermally tuned by differential thermal expansion. The achieved temperature dependence was as small as +0.01 nm/K, which is one-tenth of that of conventional semiconductor based optical filters.

1.3μm InAs quantum dots grown with an As2 source using molecular-beam epitaxy

We demonstrate the effects of using an As2 source to fabricate self-organized InAs∕GaAs quantum dot (QD) structures. QDs grown with As2 and As4 sources have narrow photoluminescence (PL) linewidths (22 and 20meV, respectively) and their respective emissions at room temperature are 1.30 and 1.29μm. QDs grown with an As2 source have a longer wavelength emission than those grown with an As4 source under all growth conditions. The density of QDs grown with an As4 source is larger and the dot size smaller than those of QDs grown with an As2 source. These results indicate that QDs grown with As2 are larger, resulting in a longer PL wavelength.

1.3-/spl mu/m InAs quantum-dot laser with high dot density and high uniformity

We realized a triple-stacked 1.3-mum InAs quantum dot (QD) with a high density of 2.4times1011 cm-2 and a high uniformity of below 24 meV that employs an As2 source and a gradient composition (GC) strain-reducing layer (SRL) grown on a GaAs substrate. We demonstrated the 1.3-mum wavelength emission of this triple-stacked QD laser with a 0.92-mm cavity length and a cleaved facet at room temperature. In addition, we realized the highest maximum modal gain yet reported of 8.1 cm-1 per QD layer at beyond 1.28 mum by using our high-density and high-uniformity QD

Highly Stacked and High-Quality Quantum Dots Fabricated by Intermittent Deposition of InGaAs

We report the successful fabrication of a highly stacked and well-aligned InGaAs quantum dot (QD) structure of over 50 layers without using a strain compensation technique by the intermittent deposition of InGaAs layers and an As2 source, resulting in no degradation in crystal quality. Intermittent deposition of InGaAs layers at relatively high temperature accounts for the formation of InGaAs QDs despite their small lattice mismatch with GaAs. The photoluminescence measurements indicate that the 50-stack InGaAs QD structures have high crystal quality, whereas the crystal quality of multistacked InAs QDs becomes much worse even with four-stack structures.

Highly stacked InGaAs quantum dot structures grown with two species of As

The authors describe successful formation of highly stacked InGaAs quantum dot (QD) structures grown with molecular beam epitaxy. 100-stack InGaAs QDs are grown without using any strain compensation technique or any degradation in crystal quality. InGaAs QDs are aligned in the growth direction and tend to align in the QD plane. As2-grown multistack InGaAs QD structures have superior optical properties to As4-grown structures at a high growth rate of 1μm∕h, whereas the opposite is true at a lower growth rate. The highest and narrowest photoluminescence spectrum is observed in a highly stacked InGaAs QD structure grown with an As2 source and a high growth rate.

2×2 Multiwavelength Micromachined AlGaAs/GaAs Vertical Cavity Filter Array with Wavelength Control Layer

We have demonstrated a novel 2×2 multiwavelength micromachined vertical cavity filter array consisting of a pair of AlGaAs/GaAs distributed Bragg reflectors (DBR). The 2×2 multiwavelength micromachined vertical cavity filter array with a wavelength span of 12 nm was fabricated by partly etching off a GaAs wavelength control layer loaded on the top surface of a device. The resonant wavelength can be adjusted by controlling the thickness of the wavelength control layer of each filter in the 2D array.

Micromachined Semiconductor Vertical Cavity for Temperature Insensitive Surface Emitting Lasers and Optical Filters

We propose a micromachined vertical cavity resonator enabling temperature insensitive operation for surface emitting lasers or optical add/drop filters. The strain-induced displacement from differential thermal expansion is used to compensate the wavelength shift caused by temperature variation. Also, a wavelength-trimming technology using the same principle with precise strain control is suggested. The possibility of a drastic reduction in the temperature sensitivity of wavelengths, as well as precise wavelength adjustment, is presented. We fabricated a micromachined vertical cavity filter with a GaAlAs/GaAs multilayer reflector, which is mechanically tuned by differential thermal expansion. We observed a large negative temperature coefficient of the resonant wavelength. It is demonstrated that its temperature dependence can be widely controlled by the proposed concept. The possibility of temperature-insensitive operation is discussed.

Micromachined GaAs/AlGaAs Resonant-Cavity Light Emitter with Small Temperature Dependence of Emission Wavelength

We present the design of novel micromachined vertical-cavity light emitters/lasers with a thermal strain control layer for temperature-insensitive operations. The temperature dependence of a resonant wavelength can be freely controlled in a micromachined cantilever structure. We demonstrated a micromachined resonant-cavity light emitter with a small temperature dependence of the emission wavelength. The temperature dependence was as small as +0.015 nm/K, which is five times smaller than that of conventional single-mode lasers.