Katsuaki Tanabe

Monolithic integration of III-V compound semiconductors on silicon is highly sought after for high-speed, low-power-consumption silicon photonics and low-cost, light-weight photovoltaics. Here we present a GaAs/Si direct fusion bonding technique to provide highly conductive and transparent heterojunctions by heterointerfacial band engineering in relation to doping concentrations. Metal- and oxide-free GaAs/Si ohmic heterojunctions have been formed at 300°C; sufficiently low to inhibit active mat

Metal nanoparticles and nanoshells consisting of metal shells and dielectric cores are known to significantly enhance incident electromagnetic fields around themselves due to surface plasmons. The field enhancement factors were calculated for spherical metal nanoparticles and nanoshells in the quasistatic limit using empirical wavelength-dependent dielectric constants. Dependence of the field enhancement factor on various parameters, such as wavelength, distance from the nanoparticle/nanoshell,

Solar cells are a promising renewable, carbon-free electric energy resource to address the fossil fuel shortage and global warming. Energy conversion efficiencies around 40% have been recently achieved in laboratories using III-V semiconductor compounds as photovoltaic materials. This article reviews the efforts and accomplishments made for higher efficiency III-V semiconductor compound solar cells, specifically with multijunction tandem, lower-dimensional, photonic up/down conversion, and plasm

A direct-bonded GaAs∕InGaAs solar cell is demonstrated. The direct-bonded interconnect between subcells of this two-junction cell enables monolithic interconnection without threading dislocations and planar defects that typically arise during lattice-mismatched epitaxial heterostructure growth. The bonded interface is a metal-free n+GaAs∕n+InP tunnel junction. The tandem cell open-circuit voltage is approximately the sum of the subcell open-circuit voltages. The internal quantum efficiency is 0.

An electrically pumped InAs/GaAs quantum dot laser on a Si substrate has been demonstrated. The double-hetero laser structure was grown on a GaAs substrate by metal-organic chemical vapor deposition and layer-transferred onto a Si substrate by GaAs/Si wafer bonding mediated by a 380-nm-thick Au-Ge-Ni alloy layer. This broad-area Fabry-Perot laser exhibits InAs quantum dot ground state lasing at 1.31 microm at room temperature with a threshold current density of 600 A/cm(2).

We fabricate a high-efficiency InAs/GaAs quantum dot (QD) solar cell. It contains five layers of high-density self-assembled InAs QDs grown by metalorganic chemical vapor deposition suppressing open-circuit-voltage (VOC) degradation. We develop a dual-layer anti-reflection coating of optimum thicknesses. The resulting cell exhibits efficiencies of 18.7% under AM1.5 G for 1 sun and 19.4% for 2 suns. Concentrator measurements demonstrate the advantage of QD use under concentrated illumination, owi

Room temperature, continuous-wave lasing in a quantum dot photonic crystal nanocavity on a Si substrate has been demonstrated by optical pumping. The laser was an air-bridge structure of a two-dimensional photonic crystal GaAs slab with InAs quantum dots inside on a Si substrate fabricated through wafer bonding and layer transfer. This surface-emitting laser exhibited emission at 1.3 microm with a threshold absorbed power of 2 microW, the lowest out of any type of lasers on silicon.

Thin-film InAs/GaAs quantum dot (QD) solar cells on mechanically flexible plastic films are fabricated. A 4.1-μm-thick compound semiconductor photovoltaic layer grown on a GaAs substrate is transferred onto a plastic film through a low-temperature bonding technique. We also fabricate thin-film InAs/GaAs quantum dot solar cells on Si substrates, as alternative low-cost, lightweight, robust substrates. The open-circuit voltages of the thin-film cells on plastic and Si substrates are equal to that

We present 1.3 µm InAs/GaAs quantum dot lasers on Si substrates operating at high temperatures. Our lasers are fabricated through epitaxial growth on GaAs substrates of the InAs/GaAs quantum dot laser double heterostructure, and subsequent GaAs/Si wafer bonding and layer transfer onto Si substrates. Both of the on-Si lasers by direct- and metal-mediated bonding exhibit lasing temperatures over 100 °C. Partial p-type doping in the InAs/GaAs quantum dot core layer is found to significantly increas

The plasmonic enhancement of electromagnetic field energy density at the sharp tips of nanoparticles or nanoscale surface roughnesses of hydrogen-absorbing transition metals, Pd, Ti, and Ni, is quantitatively investigated. A large degree of energy focusing is observed for these transition metals in the microwave region, even surpassing the enhancement for noble metals according to the conditions. Pd, for instance, exhibits peak field enhancement factors of 6000 and 2 × 108 in air for morphologic

Thin-film InAs/GaAs quantum dot solar cells on mechanically flexible plastic films are fabricated. A 4.1-μm-thick compound semiconductor photovoltaic layer was grown on a GaAs substrate, and then transferred onto a plastic film through a bonding technique. Our bonding scheme is mediated by a metal-epoxy agent for the realization of bonding at low temperatures (below 200 °C), enabling the use of plastic materials as support substrates, as well as preventing the degradation of the semiconductor ph

An InAs/GaAs quantum dot laser on a Si rib structure has been demonstrated. The double heterostructure laser structure grown on a GaAs substrate is layer-transferred onto a patterned Si substrate by GaAs/Si direct wafer bonding without oxide or metal mediation. This Fabry-Perot laser operates with current injection through the GaAs/Si rib interface and exhibits InAs quantum dot ground state lasing at 1.28 μm at room temperature, with a threshold current density of 480 A cm(-2).