A5025133025- Semiconductor Quantum Structures and Devices
- Chalcogenide Semiconductor Thin Films
- Quantum Dots Synthesis And Properties
- solar cell performance optimization
- Semiconductor materials and interfaces
- ZnO doping and properties
- GaN-based semiconductor devices and materials
- Nanowire Synthesis and Applications
- Semiconductor materials and devices
- Copper-based nanomaterials and applications
- Magnetic and transport properties of perovskites and related materials
- Magnetic properties of thin films
- Silicon Nanostructures and Photoluminescence
- Silicon and Solar Cell Technologies
- Electronic and Structural Properties of Oxides
- Perovskite Materials and Applications
- Ga2O3 and related materials
- Advanced Semiconductor Detectors and Materials
- Heusler alloys: electronic and magnetic properties
- MXene and MAX Phase Materials
- Metal and Thin Film Mechanics
- Photonic and Optical Devices
- Superconductivity in MgB2 and Alloys
- Aluminum Alloys Composites Properties
- Boron and Carbon Nanomaterials Research
The University of Tokyo
2015-2024
Tokyo University of Science
2012
Lawrence Berkeley National Laboratory
2012
Japan Science and Technology Agency
2003-2006
Extensive literature and publications on intermediate band solar cells (IBSCs) are reviewed. A detailed discussion is given the thermodynamics of energy conversion in IBSCs, device physics, carrier dynamics processes with a particular emphasis two-step inter-subband absorption/recombination that paramount importance successful implementation high-efficiency IBSC. The experimental cell performance further discussed, which has been recently demonstrated by using highly mismatched alloys...
The interaction between the magnetic dopants (Mn) and 2-dimensional hole gas (2DHG) in Mn \ensuremath{\delta}-doped GaAs/Be-doped $p$-type AlGaAs heterostructures, where holes were supplied from Be-doped to GaAs, realized ferromagnetic ordering. Curie temperature ${T}_{\mathrm{C}}$ of heterostructure prepared with suitable growth conditions was 172 K, highest among values reported III-V (InAs, GaAs) semiconductors.
We show that suitably designed magnetic semiconductor heterostructures consisting of Mn delta ($\ensuremath{\delta}$)-doped GaAs and $p$-type AlGaAs layers, in which the locally high concentration moments atoms are controllably overlapped with two-dimensional hole gas wave function, realized remarkably ferromagnetic transition temperatures (${T}_{\mathrm{C}}$). A significant reduction compensative interstitials by varying growth sequence structures followed low-temperature annealing led to...
We present evidence for the production of photocurrent due to two-photon excitation in an intermediate band solar cell structure. The structure consists n-GaNAs layer sandwiched between a p-AlGaAs emitter and n-AlGaAs barrier with suitable doping level block electron escaping from bottom n-GaAs substrate. Multi-band transitions observed experiments are explained using photo-modulated reflectance spectrum, further support operation this is given by current-voltage measurements.
Abstract An improved photocurrent production is demonstrated in dilute nitride GaInNAsSb solar cells grown by molecular beam epitaxy. The photovoltaic properties were investigated increasing the thickness of layers from 1.0 to 3.0 µm. amount photon absorption increased with thickness. Yet an incomplete photocarrier collection was observed 2.0‐ and 3.0‐µm‐thick devices. This feature due a partial lack electric field region. In order for complete carrier aided field, background‐doping level...
We present a comparative study on the material properties and two-photon excitation (TPE) experiments that involve three bands between GaNAs GaNAsSb absorber designed for intermediate band solar cells. The layers were sandwiched p-AlGaAs emitter n-AlGaAs IB barrier layers. This permits production of above bandgap electron-hole pairs by TPE involving two subband photons with as stepping stone. A recovery in carrier population was realized due to an improved quality. An enhancement...
We demonstrate the electrical and optical control of ferromagnetism in semiconductor heterostructures at high temperatures 100–117 K. The consist Mn delta (δ)-doped GaAs p-type AlGaAs. are able to isothermally change paramagnetic state ferromagnetic vice versa, by applying a gate electric-field or light irradiation. large modulation TC (ΔTC∼15 K) (>∼100 demonstrated here may pave way for functional device applications compatible with present technology.
A large positive magnetoresistance (MR) at room temperature was observed in a GaAs:MnAs granular thin film, which MnAs nanoclusters were embedded GaAs matrix. Current-voltage characteristics and MR effect of the film measured by two-point-probe method. The ratio reached more than 600%, when bias voltage 110 V applied to film.
We have studied the planar Hall effect (PHE) in a Mn $\ensuremath{\delta}$-doped GaAs-based heterostructure consisting of GaAs and $p$-type AlGaAs. observe distinct large PHE specific in-plane [110] uniaxial magnetic anisotropy below ferromagnetic transition temperature $({T}_{\mathrm{C}})$. This is found dominant over biaxial cubic anisotropy, clearly identified by angular dependence PHE. observation quantitatively discussed terms two models magnetization reversal: coherent rotation model...
We have grown Mn δ-doped GaAs layers on GaAs(001) substrates by molecular beam epitaxy. Secondary ion mass spectroscopy and transmission electron microscopy revealed that dopants were abruptly confined. The doping profiles still retained abruptness even at elevated growth temperature up to 400 °C. samples showed high resistivity low did not show a ferromagnetic behavior. However, in selectively doped heterostructure (Mn / Be-doped AlGaAs), where holes supplied from the AlGaAs layer, order...
As a well-explored chalcopyrite material, copper gallium sulfide CGS has been considered potential material for solar cell absorber layers. However, its photovoltaic attributes still require to be improved. In this research, novel telluride CGST, deposited and verified as thin film layer fabricate high-efficiency cells by experimental testing numerical simulations. The results display the intermediate band formation in CGST with incorporation of Fe ions. Electrical studies showed enhancement...
This work studies the impact of optimal postannealing on 1.0 eV GaInNAsSb solar cells for application to high‐efficiency multijunction cells. Compared our past report in which reasonably good cell performance was achieved devices annealed at 850 °C, further optimization carried out order lower temperature. Both light current–voltage and internal quantum efficiency (IQE) characteristics reveal that significant improvements device qualities can be obtained with annealing temperatures. For...