Yoshihiro Hamakawa

Bio: Yoshihiro Hamakawa is an academic researcher from Osaka University. The author has contributed to research in topics: Amorphous silicon & Thin film. The author has an hindex of 43, co-authored 435 publications receiving 7267 citations.

Properties and structure of a‐SiC:H for high‐efficiency a‐Si solar cell

Abstract: A series of experimental investigations on optical and optoelectronic properties of methane‐ and ethylene‐based a‐SiC:H films has been made. The chemical bonding structure of two kinds of a‐ SiC:H films has also been explored from infrared (IR) absorption structural analysis. An experimental verification for the wide gap window material in the amorphous silicon solar cell is shown on methane‐ and ethylene‐based a‐SiC:H. The methane‐based a‐SiC:H film shows one or two orders of magnitude larger photoconductivity recovery effect of doping than the ethylene‐ based one. IR absorption analysis shows that the methane‐based a‐SiC:H film is recognized as a rather ideal amorphous SiC alloy as compared with the ethylene‐based one. It has been found through these investigations that the methane‐based a‐SiC:H film is superior to the ethylene‐ based one as a window material. Utilizing the methane‐based a‐SiC:H, an 8% efficiency barrier has been broken through with an a‐SiC:H/a‐Si:H heterojunction structure.

Cu(In,Ga)Se2 solar cells with controlled conduction band offset of window/Cu(In,Ga)Se2 layers

Abstract: Our group studied the effects of conduction band offset of window/Cu(In,Ga)Se2 (CIGS) layers on CIGS-based solar cell performance. To control the conduction band offset, we considered the use of a window layer of Zn1−xMgxO thin film with a controllable band gap as an alternative to the conventional window layer using CdS film. From the measurement of valence band offset between Zn1−xMgxO/CIGS layers and the band gap of each layer, we confirmed that the conduction band offset of Zn1−xMgxO/CIGS layers could be controlled by changing the Mg content of the Zn1−xMgxO film. The CIGS-based solar cells prepared for this study consisted of an ITO/Zn1−xMgxO/CIGS/Mo/soda-lime glass structure. When the conduction band minimum of Zn1−xMgxO was higher than that of CIGS, the performance of CIGS-based solar cells with a Zn1−xMgxO window layer was equivalent to that of CIGS-based solar cells with CdS window layers. We confirmed that the control of the conduction band offset of the window/CIGS layers decreases the majority...

Flexible photovoltaic device

Abstract: A flexible photovoltaic device includes a flexible substrate and a photovoltaic device body. The flexible substrate is a metal foil or film provided with an electric insulating layer of a material having an electric conductivity of not more than 10-7 (Ω·cm.)-1 at the time of light impinging and selected from a heat resistant polymer, a metal oxide, a crystalline or amorphous silicon compound and an organometallic compound.

Preparation and basic properties of PbTiO3 ferroelectric thin films and their device applications

Abstract: A series of technical data for preparing PbTiO3 ferroelectric thin films and their applications to some electronic devices have been presented. PbTiO3 thin films having considerably good ferroelectric properties have been obtained by rf sputtering or CVD. Maximum dielectric constant and remanent polarization are about 200 and 27μC/cm2, respectively. Several attempts to fabricate electronic devices such as nonvolatile memory, infrared sensor, ultrasonic sensor and low-threshold electroluminescent devices have been also carried out.

Band parameters for III–V compound semiconductors and their alloys

Abstract: We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Semiconducting and other major properties of gallium arsenide

Abstract: This review provides numerical and graphical information about many (but by no means all) of the physical and electronic properties of GaAs that are useful to those engaged in experimental research and development on this material. The emphasis is on properties of GaAs itself, and the host of effects associated with the presence of specific impurities and defects is excluded from coverage. The geometry of the sphalerite lattice and of the first Brillouin zone of reciprocal space are used to pave the way for material concerning elastic moduli, speeds of sound, and phonon dispersion curves. A section on thermal properties includes material on the phase diagram and liquidus curve, thermal expansion coefficient as a function of temperature, specific heat and equivalent Debye temperature behavior, and thermal conduction. The discussion of optical properties focusses on dispersion of the dielectric constant from low frequencies [κ0(300)=12.85] through the reststrahlen range to the intrinsic edge, and on the ass...

Superconductivity in the presence of strong Pauli paramagnetism : CeCu2Si2

Abstract: A comparison was made between four low-temperature properties of LaCu2Si2and CeCu2Si2. Whereas LaCu2Si2behaves like a normal metal, CeCu2Si2shows (i) low-temperature anomalies typical of “unstable 4f shell” behavior and (ii) a transition into a superconducting state atT c ≃ 0.5 K. Our experiments demonstrate for the first time that superconductivity can exist in a metal in which many-body interactions, probably magnetic in origin, have strongly renormalized the properties of the conduction-elec-tron gas.

Thin-film solar cells: an overview

Abstract: Thin film solar cells (TFSC) are a promising approach for terrestrial and space photovoltaics and offer a wide variety of choices in terms of the device design and fabrication. A variety of substrates (flexible or rigid, metal or insulator) can be used for deposition of different layers (contact, buffer, absorber, reflector, etc.) using different techniques (PVD, CVD, ECD, plasma-based, hybrid, etc.). Such versatility allows tailoring and engineering of the layers in order to improve device performance. For large-area devices required for realistic applications, thin-film device fabrication becomes complex and requires proper control over the entire process sequence. Proper understanding of thin-film deposition processes can help in achieving high-efficiency devices over large areas, as has been demonstrated commercially for different cells. Research and development in new, exotic and simple materials and devices, and innovative, but simple manufacturing processes need to be pursued in a focussed manner. Which cell(s) and which technologies will ultimately succeed commercially continue to be anybody's guess, but it would surely be determined by the simplicity of manufacturability and the cost per reliable watt. Cheap and moderately efficient TFSC are expected to receive a due commercial place under the sun.