Hitoo Iwasa

Bio: Hitoo Iwasa is an academic researcher from Osaka University. The author has contributed to research in topics: Wafer & Passivation. The author has an hindex of 10, co-authored 28 publications receiving 489 citations.

Nitric acid oxidation of Si to form ultrathin silicon dioxide layers with a low leakage current density

Abstract: Ultrathin silicon dioxide (SiO2) layers with excellent electrical characteristics can be formed using the nitric acid oxidation of Si (NAOS) method, i.e., by immersion of Si in nitric acid (HNO3) solutions. The SiO2 layer formed with 61 wt % HNO3 at its boiling temperature of 113 °C has a 1.3 nm thickness with a considerably high density leakage current. When the SiO2 layer is formed in 68 wt % HNO3 (i.e., azeotropic mixture with water), on the other hand, the leakage current density (e.g., 1.5 A/cm2 at the forward gate bias, VG, of 1 V) becomes as low as that of thermally grown SiO2 layers, in spite of the nearly identical SiO2 thickness of 1.4 nm. Due to the relatively low leakage current density of the NAOS oxide layer, capacitance–voltage (C–V) curves can be measured in spite of the ultrathin oxide thickness. However, a hump is present in the C–V curve, indicating the presence of high-density interface states. Fourier transformed infrared absorption measurements show that the atomic density of the SiO...

Solid-Stated Image Pickup Device And Method For Manufacturing Same

Abstract: There are provided image pickup devices capable of significantly increasing production yield and ensuring long-term reliability and a method for manufacturing the image pickup devices. This invention is characterized in that it has a large number of light-receiving portions 2 formed at a surface portion of a wafer 1 and a microlens 3 formed for each of the light-receiving portions, through electrodes 4 for performing supply of power to the light-receiving portions 2 and passing and reception of an electrical signal are provided all over the periphery of the wafer 1 , one end of each through electrode 4 is connected to an electrode pad 4 a which is connected to a wire leading to a light-receiving element at the surface portion of the wafer 1 , the other end is connected to a wire through a back electrode 5 , a rib 7 which serves as a partition portion arranged to surround the microlenses 3 on four sides is provided on the surface of the wafer 1 , a transparent plate 8 of optical glass or the like is bonded to an upper surface of the rib 7 with adhesive, and a protective frame 10 is provided at a junction between the rib 7 and the transparent plate 8.

Spectroscopic and electrical properties of ultrathin SiO2 layers formed with nitric acid

Abstract: Spectroscopic and electrical properties of ultrathin silicon dioxide (SiO2) layers formed with nitric acid have been investigated. The leakage current density of the as-grown SiO2 layers of 1.3 nm thickness is high. The leakage current density is greatly decreased by post-oxidation annealing (POA) treatment at 900 � C in nitrogen, and consequently it becomes lower than those for thermally grown SiO2 layers with the same thickness. X-ray photoelectron spectroscopy measurements show that high density suboxide species are present before POA and they are markedly decreased by POA. Fourier transformed infrared absorption measurements show that water and silanol group are present in the SiO2 layers before POA but they are removed almost completely by POA above 800 � C. The atomic density of the as-grown chemical SiO2 layers is 4% lower than that of bulk SiO2 layers, while it becomes 12% higher after POA. It is concluded that the high atomic density results from the desorption of water and OH species, and oxidation of the suboxide species, both resulting in the formation of SiO2. The valence band discontinuity energy at the Si/SiO2 interface increases from 4.1 to 4.6 eV by POA at 900 � C. The high atomic density enlarges the SiO2 band-gap energy, resulting in the increase in the band discontinuity energy. The decrease in the leakage current density by POA is attributed to (i) a reduction in the tunneling probability of charge carriers through SiO2 by the enlargement of the band discontinuity energy, (ii) elimi- nation of trap states in SiO2, and (iii) elimination of interface states. � 2003 Elsevier B.V. All rights reserved.

Electroless Nickel Plating on Silicon

Abstract: In the study of electroless Ni plating of Si wafers with p‐n junctions using conventional solutions, a pronounced difference in plating rate between p‐ and n‐type surfaces is observed. Further experiments show that rate difference probably should not only be attributed to the photovoltaic effect generated at the p‐n junctions but also to the electronegativity difference between p‐ and n‐type Si. The latter effect can be changed by addition of such material as or to the plating solution. Whereas addition increases the rate difference, EDTA addition decreases it. This fact which can be put to practical use gives an extra support for the explanation given above.

Experimental and theoretical studies of Si–CN bonds to eliminate interface states at Si/SiO2 interface

Abstract: Cyanide treatment, which includes the immersion of Si in KCN solutions followed by a rinse, effectively passivates interface states at Si/SiO 2 interfaces by the reaction of CN − ions with interface states to form Si–CN bonds. X-ray photoelectron spectroscopy (XPS) measurements show that the concentration of the CN species in the surface region after the cyanide treatment is ∼0.25 at.%. Take-off angle-dependent measurements of the XPS spectra indicate that the concentration of the CN species increases with the depth from the Si/SiO 2 interface at least up to ∼2 nm when ultrathin SiO 2 layers are formed at 450 °C after the cyanide treatment. When the cyanide treatment is applied to metal–oxide–semiconductor (MOS) solar cells with 〈ITO/SiO 2 /n-Si〉 structure, the photovoltage greatly increases, leading to a high conversion efficiency of 16.2% in spite of the simple cell structure with no pn-junction. Si–CN bonds are not ruptured by air mass 1.5 100 mW cm −2 irradiation for 1000 h, and consequently the solar cells show no degradation. Neither are Si–CN bonds broken by heat treatment at 800 °C performed after the cyanide treatment. The thermal and irradiation stability of the cyanide treatment is attributable to strong Si–CN bonds, whose bond energy is calculated to be 1 eV higher than that of the Si–H bond energy using a density functional method.

Semiconductor device, and manufacturing method thereof

Abstract: An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Substrate with a photocatalytic coating

Abstract: The subject of the invention is a glass-, ceramic- or vitroceramic-based substrate (1) provided on at least part of at least one of its faces with a coating (3) with a photocatalytic property containing at least partially crystalline titanium oxide. It also relates to the applications of such a substrate and to its method of preparation.

Tunnel oxide passivated contacts as an alternative to partial rear contacts

Abstract: Recently, n-type Si solar cells featuring a passivated rear contact, called TOPCon (Tunnel Oxide Passivated Contact) were reported. The high conversion efficiency of 24.4% and very high FF>82% demonstrates that the efficiency potential of this full-area passivated rear contact is as good as or even better than that of partial rear contact (PRC) schemes like PERL (passivated emitter and rear locally diffused) and in addition avoids complex structuring steps and features a 1D carrier transport. Likewise, a boron-doped passivated rear contact for p-type solar cells (p-TOPCon) is proposed as an alternative to p-PRC cells. The optimum device design of PRC cells has to account for two opposing effects: a low-loss 3D carrier transport requires a high base doping but Shockley–Read–Hall (SRH) recombination within the base due to the formation of boron–oxygen complexes in standard Cz silicon calls for a low base doping level. This conflict might be overcome by p-TOPCon because its performance is less sensitive to base doping. This will be discussed on the base of experimental results. It is shown that its high implied fill factor (iFF) of 84% combined with the 1D carrier transport in the base translates into a higher FF potential. First investigations on planar solar cells prove the good performance of the p-TOPCon with respect to passivation and carrier transport. A Voc of 694 mV and a FF of 81% underline the efficiency potential of this rear contact.

Tunnel oxide passivated carrier-selective contacts based on ultra-thin SiO2 layers

Abstract: Carrier-selective contacts are one of the key enabling technologies to approach very high conversion efficiencies close to the theoretical limit of silicon solar cells. The tunnel oxide passivated contact (TOPCon) approach is an alternative to classical heterojunction solar cells enabling efficiencies up to 24.4%. The tunnel oxide is a core element of this contact as it has to reduce the minority carrier recombination but simultaneously must not hamper the majority carrier flow. This paper focuses on ozone-based oxidation techniques, which can potentially be cost effective and industrially feasible methods for the realization of ultra-thin tunnel oxide layers as an alternative to the oxidation in nitric acid (HNO3) reference process. All investigated oxides were applied to the electron-selective contact (n-TOPCon) on planar and textured surfaces. It will be shown that both ozone based oxidation techniques (UV/O3 photo-oxidation and wet-chemical oxidation in ozonized DI-H2O) enable high implied open circuit voltage (iVOC) values exceeding 720 mV on planar and 710 mV on textured surfaces, respectively. Further oxide properties as stoichiometry and layer thickness were analyzed by means of X-ray photoelectron spectroscopy (XPS), spectral ellipsometry (SE) and transmission electron microscopy (TEM). In compliance with earlier results it was found that a minimum oxide layer thickness (approximately 1.3 nm) and a high amount of oxygen-rich sub oxide species are required to obtain a good surface passivation. Using such oxides, a wider range of temperatures can be used during the TOPCon annealing. Applying the ozone-based oxide layers to n-TOPCon solar cells resulted in a high VOC of up to 719 mV and a peak efficiency of 24.9%. Similar results were obtained with the HNO3 reference process (VOC=716 mV, η=24.8%).

Record High Efficiency Single-Walled Carbon Nanotube/Silicon p-n Junction Solar Cells

Abstract: Carrier transport characteristics in high-efficiency single-walled carbon nanotubes (SWNTs)/silicon (Si) hybrid solar cells are presented. The solar cells were fabricated by depositing intrinsic p-type SWNT thin-films on n-type Si wafers without involving any high-temperature process for p–n junction formation. The optimized cells showed a device ideality factor close to unity and a record-high power-conversion-efficiency of >11%. By investigating the dark forward current density characteristics with varying temperature, we have identified that the temperature-dependent current rectification originates from the thermally activated band-to-band transition of carriers in Si, and the role of the SWNT thin films is to establish a built-in potential for carrier separation/collection. We have also established that the dominant carrier transport mechanism is diffusion, with minimal interface recombination. This is further supported by the observation of a long minority carrier lifetime of ∼34 μs, determined by t...