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The cost of solar cell production can be reduced by wafer thinning. A thinner wafer provides flexibility, and crystalline silicon solar cells are promising as flexible solar cells due to their flexibility. However, as wafers become thinner, production yield decreases due to wafer breakage caused by sawing damage; thus, to further reduce wafer thickness, it is necessary to suppress sawing damage. We investigated the flexibility of wafers under various slice conditions by conducting biaxial bending tests and clarified the dominant factor causing sawing damage to further reduce the wafer thickness for crystalline silicon solar cells. The results of damage observation by scanning electron microscopy and evaluation of the crystal structure by Raman spectroscopy confirm that the damage structure changes significantly depending on wire specifications. The results from the biaxial bending tests indicate that the three-dimensional flexibility of a wafer is determined by wire specifications.

In this study, we investigated the optical properties, band gap, dielectric function and absorption coefficient of Sn-based perovskites, which are considered as potential candidates for Pb-free perovskite solar cells. In addition, the quantum efficiency of the perovskite solar cell was investigated, and the values were compared with the experimental values. Furthermore, as an element that suppresses Sn vacancy formation, we focused on the B site of MASnI3 and investigated the vacancy formation energy by substituting various elements. The absorption coefficient was calculated to investigate the effects on the optical characteristics of an additive element that suppresses Sn vacancies.

We establish the method for estimating the stray elements of the GaN-WPT circuit by measuring the radiated emission around the GaN switching device. By controlling the circuit supply voltage, the spectrum peak shift due to the output capacitance of the GaN-HEMT is observed. It is found that these peak shift characteristics include the influence of both the stray wire inductance and stray capacitance. By fitting using the series resonance model, the value of the stray inductance and stray capacitance can be estimated in the non-destructive measurement in the GaN-WPT circuit.

The dynamic characteristics of GaN-based vertical-cavity surface-emitting laser (VCSEL) with an AlInN/GaN semiconductor distributed Bragg reflector has been reported for the first time. The max dynamic lasing frequency of 1.1 GHz with a wavelength of 415 nm and a threshold current of 7 mA has been demonstrated. Moreover, at the pulse lasing operation, both the steep lasing waveforms and the tailing spontaneous emission waveforms were observed in driven with the square pulse waveforms. The dynamic lasing frequency driven by the sine waveform seems to be related to this steep lasing waveform at the square pulse operation. During these dynamic measurements, the lasing characteristics of the VCSEL were gradually degraded, and the lasing power is decreased by −7 dB at the same bias condition after several hours.

In this paper, we describe a fabrication procedure for large-diameter carbon nanotube probe tips (CNT tips) for atomic force microscopy, the tip-end chemistry of the CNT tips, and their advantage drawn from the study of adhesion force imaging in an ambient atmosphere on a patterned hydrophobic and hydrophilic self-assembled monolayer, which has been prepared by a microcontact printing method. Force titration measurements in phosphate buffer solutions reveal that the CNT tip has retained carboxyl groups at its end. In adhesion force imaging, a distinct chemical contrast is obtained for the patterned surfaces as compared to a case using a silicon nitride tip. The origin of the distinct contrast is discussed in terms of the tip-end chemistry featured by carboxyl groups and a possible weakening of capillary forces of water caused at around the tip–sample interface because of the intrinsically hydrophobic nature of CNTs.

In order to improve the ferroelectric properties of films for ferroelectric memories or relaxor single crystals for actuators, it is necessary to observe domain structures on the nanoscale. We propose an approach to observing three-dimensional (3D) domain structures by ultrasonic atomic force microscopy (UAFM) with a subsurface observation capability. Moreover, it is sometimes necessary to observe the motion of the 3D domain structures under an electric field. We propose for this case a method of applying an electric field using a surface electrode pair (SEP) in the observation plane of UAFM. When applying a field to a lead magnesium niobate–lead titanate [0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3: PMN–PT] single crystal, reversible domain switching was observed at low fields, and irreversible switching with domain boundary (DB) motion was observed at high fields. In the latter case, the growth of the domain was observed with the subsurface DB motion. A SEP and UAFM are thus proved useful in evaluating the motion of domain structures in ferroelectrics.

We investigated the gate-length dependence of room-temperature DC operation in submicron-gate AlGaN/GaN high-electron-mobility transistors (HEMTs). The threshold voltage was reduced by the short-channel effect, which is only dependent on the aspect ratio of the gate length to the barrier-layer thickness. On the other hand, the transconductance was restricted by the source resistance, and was dependent on not only the gate length LG but also the source?gate length LSG. The transconductance was increased by reducing LSG rather than LG in the submicron-gate HEMTs.

We proposed a new signal quality evaluation method applying a sequenced amplitude margin (SAM) for over 30-GB Blu-ray discs (BDs), where the dominant error pattern differs from lower-density discs (23–27-GB BDs), and conventional signal quality evaluation method such as maximum-likelihood sequence error (MLSE) lose accuracy. We experimentally confirmed the effectiveness of our new method for 30–31.5-GB BDs.

Irradiation damage in an SiO2/Si system induced by photons and/or ions was evaluated. The flat-band voltage (Vfb) was not shifted and the interface density of states (Dit) was increased by irradiation of 172-nm-wavelength light, which corresponds to a photo-oxidation condition. Surface wave plasma (SWP) excited using microwave with Kr gas has an electron temperature less than 1 eV. However, Vfb was shifted and Dit was increased by the irradiation of photons from Kr plasma, which corresponds to a plasma-oxidation condition. Vfb was not shifted and Dit was increased by the irradiation of ions from Kr plasma. However, the SiO2/Si interface formed by photo-oxidation had a Dit of 3×1010 cm-2eV-1, which is equal to that of a SiO2/Si interface formed by a thermal-oxidation. This means that photo-oxidation forms the SiO2/Si interface by a concerted reaction of the photo-oxidation and the irradiation.

New planarization technology of SiO2 films employing anhydrous HF (AHF) gas with no slurry was studied. In this planarization, the chemical reactions were dominant: consequently, soft planarization with no mechanical polishing was achieved. In this AHF planarization (AHFP) method, anisotropic etching of SiO2 film using AHF gas, the so-called "Dry Ox Process" was applied. The Dry Ox Process was observed in a SiO2 surface covered with negative-tone-photo-resist in 1977. We accidentally found similar effects employing conventional positive-tone-photoresist (OFPR-800), and other types of resists. We applied the newly found condition to AHFP. Only the contact of OFPR film to the SiO2 film generated the condensed layer on the surface of SiO2, consequently, initiation of AHFP was observed. However, the planarization process stopped within 1 min. This was considered that the active hydrogen on the surface of the OFPR was consumed. Eventually, the steps between the convexo-concave features were considerably reduced, improvement of film materials will be required for complete planarization.

Electron cyclotron resonance-reactive ion etching (ECR-RIE) is very useful for fabricating semiconductor photonic devices and integrated circuits (PICs). The mixture gas of CH4/H2 is used for etching III-V semiconductors, but the carbon polymer film deposited on the surface during the etching process presents some problems. Thus, the polymer film must be ashed off using an O2 plasma. We introduced the cyclic injection of CH4/H2/Ar and O2 to ECR-RIE, and demonstrated that it was very useful for etching of InP. However, compound semiconductors containing Al (e.g., AlGaAs and InAlAs) react with oxygen and an alumina layer is formed, which cannot be etched by CH4/H2 etching. Therefore, we used a new cyclic etching process with constant Ar flow in the chamber to remove this alumina layer by Ar ion etching, and obtained good results for etching rate and surface morphology for the compound semiconductors containing Al. We also proposed a suitable combination of three cyclic etching procedures (continuous etching, cyclic etching without constant Ar flow and cyclic etching with constant Ar flow) for etching the multilayer heterostructure of III-V semiconductors including InP and/or compound semiconductors containing Al.

A new type of surface acoustic wave (SAW) coupler has been proposed, which is composed of a cascaded group type unidirectional interdigital transducer (UDT) structure to achieve desired performances without gratings and external phase shifters. In order to confirm the performances, simulations and experiments are applied. Predictions are also verified by simulations and experiments. A linear circuit composition procedure for multiport elements is applied in order to explain the meander resistive effect. Cascade-connected ports are prepared for the meander electrode. An improved cascaded UDT structure has been proposed to achieve wideband performances. A filter with a bandwidth twice as that of the conventional one is obtained. Furthermore the structure is applied to a Ring-type filter. High sidelobe rejection and low loss performances, and the miniature chip size of the filer are observed.

We attempted a new ohmic contact process for two-step metallization, and demonstrated improvement of the ohmic properties and device characteristics. The contact resistance of the two-step ohmic process was improved from 4.2 Ωmm obtained in a conventional contact to 2.6 Ωmm. The specific contact resistivity of the transmission line method ohmic contacts improved by one order of magnitude, from 10-4 Ω-cm2 in the conventional contact sample to 10-5 Ω-cm2 in the two-step contact sample treated with Cl2 plasma. The dc measurements of the HFETs showed improved current-voltage curves in the two-step contact samples. The values of Ron of the AlGaN/GaN HFET with the two-step contact process and the conventional HFET were calculated to be 0.23 mΩ-cm2 and 0.28 mΩ-cm2 in the linear (ohmic) region, respectively.

Amorphous Si (a-Si:H) and microcrystalline Si (µc-Si:H) materials were successfully deposited by the Hot Wire Cell method. We have studied these materials from the viewpoint of improving their qualities and the solar cell performances. As a result, it was found that the peak at 2100 cm-1 which originates from Si–H2 bonding in the infrared absorption spectra could be dramatically reduced at a low deposition pressure of 10 mTorr. Furthermore, it was shown by secondary ion mass spectroscopy (SIMS) analysis that the concentrations of O and C atoms in a-Si:H films could be reduced to the order of 1018 cm-3 at low deposition pressures of 1–10 mTorr. The conversion efficiency of 7.5% was achieved for superstrate-type pin a-Si solar cells with a deposition rate of 0.4 nm/s under AM1.5 insolation.

It is difficult to optimize the write strategy by conventional methods in high-density recording systems with very severe intersymbol interference. We have proposed a new method using the index accounting for the linearity of the channel, which is very important in the partial-response-maximum-likelihood detection scheme. It has been confirmed that the minimum bit error rate can be obtained when the linearity of the channel becomes maximum. We have shown the feasibility of a recording capacity of over 20 GB with 120-mm-diameter phase-change media using the blue-violet laser diode with an objective lens whose numerical aperture is 0.65.

Microcrystalline silicon (µc-Si) films and solar cells were prepared by mercury-sensitized photochemical vapor deposition (photo-CVD). The changes in the structural properties of a series of µc-Si films grown under various H2 dilution and deposition pressure conditions were discussed. The results indicated that the properties of µc-Si films depend strongly on the atomic hydrogen. The microstructures of µc-Si films on textured SnO2 with different haze factors (from 13% to 65%) were observed with a scanning electron microscope and a transmission electron microscope. The observations revealed that the µc-Si layers grew from the initial stage of deposition with columnar grains and that they were conformal to the surface of textured SnO2. The grain boundary density of µc-Si film on SnO2 with higher haze factors was lower than that on SnO2 with lower haze factors. The effect of textured SnO2 with different haze ratios on p–i–n µc-Si cell characteristics was discussed and it was found that the higher haze factors showed a higher degree of light trapping in our µc-Si cells. We deposited µc-Si cells with an intrinsic µc-Si layer thickness of 430 nm on a textured SnO2 sample with a haze factor of 42% and achieved a conversion efficiency of 6.55%.

High-structural-quality c-axis GaN layers were grown on (0001) sapphire substrates by N2-plasma-assisted molecular-beam epitaxy (MBE) using a double-step AlN buffer layer process. The introduction of double-step AlN buffer layers grown at two different high temperatures improved the quality of the GaN layers dramatically. The full-width at half maximum (FWHM) (ω scan) of GaN layers along the symmetric (0002) and asymmetric (1011) diffraction planes were 104 and 848 arcsec, respectively, whereas they were 532 and 1335 arcsec for the GaN layers grown by a single-step AlN buffer process. Double-step AlN buffers improve the structural quality of the layers and decrease the X-ray dislocation density. We have shown that the quality of the underlying AlN buffer layer is the determining factor in the successful growth of high-quality GaN epitaxial layers.

We investigate the effect of strain state on ultrathin AlN/GaN superlattice (SL) growth by metalorganic chemical vapor deposition. It is found that the strain state (tensile or compressive) plays a role in periodic structure formation. A well-ordered SL growth with excellent periodicity can be realized under a tensile strain. However, a disordered SL structure is formed under a compressive strain. Furthermore, the ordered SL growth can be restored by inverting the strain state. Our findings show the importance of strain engineering in nanoscale structure growth.

The technical difficulty of balancing large data capacity with a high data transfer rate in holographic data storage systems (HDSSs) is significantly high because of tight tolerances for physical perturbation. From a system margin perspective in terabyte-class HDSSs, the positioning error of a holographic disc should be within about 10 µm to ensure high readout quality. Furthermore, fine control of the positioning should be accomplished within a time frame of about 10 ms for a high data transfer rate of the Gbps class, while a conventional method based on servo control of spindle or sled motors can rarely satisfy the requirement. In this study, a new compensation method for the effect of positioning error, which precisely controls the positioning of a Nyquist aperture instead of a holographic disc, has been developed. The method relaxes the markedly low positional tolerance of a holographic disc. Moreover, owing to the markedly light weight of the aperture, positioning control within the required time frame becomes feasible.

For applications to a novel low-voltage acceleration field emission display, carbon nanofiber (CNF) emitters were fabricated using a screen printing method. The two types of CNF of different lengths, normal-length CNFs, and cut CNFs were examined. A current density of 1.4 mA/cm2 was achieved at 10 V/µm in CNF emitters prepared from the paste composed of normal-length CNFs (1 wt %), glass paste (6 wt %), and gold nanometal ink (30 wt %). The field enhancement factor β in the Fowler–Nordheim equation was ca. 5800. CNF emitters without gold nanometal ink showed low performance. Emitter performance was determined on the basis of the results of scanning electron microscopy (SEM) and field emission characteristics.

We investigated the inductively coupled plasma etching of InP-based materials for photonic-crystal (PC) device fabrication. By optimizing bias power and gas pressure, circular holes with a diameter of

The effect of double thin AlN/GaN superlattice interlayers (SL ILs) on the growth of thick GaN epilayers by metalorganic chemical vapor deposition (MOCVD) on Si(110) substrates is investigated. It is found that the GaN middle layer (GaN layer between the two SL ILs) can affect the strain state of the GaN epilayer. By comparison with the case of a single SL IL, it is shown that the double SL ILs can have a stronger compressive effect on the GaN epilayer grown on it, which results in lower residual tensile strain in the GaN film after the growth. By optimizing the GaN middle layer thickness, a 4-µm-thick crack-free GaN epilayer is successfully achieved. By this simple technique, it is expected that high-quality crack-free thick GaN can be grown on Si substrates for optical and electronic device applications.

The bonding of metal electrodes and insulator hybrid interfaces is one of the key techniques in three-dimensional integration technology. Metal materials such as Cu or Al are easily directly bonded by surface activated bonding at room temperature, but insulator materials such as SiO2 or SiN are not. Using only Si ultrathin films, we propose a new bonding technique for SiO2/SiO2 bonding at room temperature. Two SiO2 surfaces, on which Si thin films were deposited, were contacted in vacuum. We confirmed that the thickness of the layer was about 7 nm by transmission electron microscopy observation and that the layer was non crystalline by electron energy loss spectroscopy analysis. No metal material was found in the bonding interface by energy-dispersive X-ray spectroscopy analysis. The surface energy was about 1 J/m2, and the bonding strength was more than 25 MPa. This bonding technique was successfully realized to enable SiO2/SiO2 bonding without a metal adhesion layer.

Owing to the formation of the charge transfer (CT) state, the open-circuit voltage (V oc) of organic photovoltaic (OPV) devices commonly suffers an energy loss of 0.8–1.3 eV from the effective bandgap. Benzotrithiophene (BTT)-based low-bandgap polymers that we have recently reported showed deep HOMO levels (−5.4 to −5.6 eV) and moderate optical bandgaps of 1.7–1.8 eV, which resulted in high V oc’s of 0.78–0.98 V and relatively low energy losses when blended with methano[60]fullerene (PCBM). Here, we report the temperature-dependent dark current analysis of organic solar cells of BTT copolymers:PCBM blends. Shockley diode analyses revealed the dominant contribution of CT energy and concomitant pre-exponential factor of dark saturation current density associated with charge recombination. The findings could establish a fundamental aspect to draw a design rule in BTT-based polymers towards their evolutions in OPV devices.

Roles of Si irradiation during GaN growth interruption in plasma-assisted molecular beam epitaxy are studied. It is found that irradiated Si can modulate the GaN surface energy to enhance the Ga surface diffusion, resulting in a flat GaN surface with monolayer steps as determined by atomic force microscopy observations. Furthermore, cross-sectional transmission electron microscopy reveals that threading dislocations in a GaN film can be greatly reduced by Si irradiation, which agrees very well with the results of high-resolution X-ray diffraction measurement of asymmetric (102) GaN diffraction. These two positive effects of Si irradiation are promising for growing high-quality GaN with excellent surface morphology and low dislocation density for device applications.

We present the characteristics of a novel AlN/AlGaN/GaN metal insulator semiconductor heterostructure field-effect transistor (MIS-HFET) structure with an AlN cap layer as a gate insulating layer. The gate leakage current for the AlN/AlGaN/GaN MIS-HFET was shown to be more than three orders of magnitude smaller than that for the AlGaN/GaN HFET at around -20 V gate bias. This demonstrates that the wide band gap AlN/AlGaN gate structure suppresses the gate leakage current, resulting in improved device characteristics compared with common HFETs in this study. A maximum gm of 134 mS/mm was observed at a 4 V drain-source bias of a MIS-HFET with a gate length (Lg)=0.85 µm, gate width (Wg)=57 µm, and drain-source spacing (Lds)=3 µm. A threshold voltage (Vt) of -3.06 V and a maximum channel current of 551 mA/mm were observed.

Accepted: 2011-03-12, 資料番号: SA1003077000

The distribution and behavior of hydrogen in a SiO2/SiN/SiO2 (ONO) film stack structure with thermal treatment were investigated by high-resolution secondary ion mass spectrometry analysis. Hydrogen atoms were present in the poly-Si/top-SiO2 interface, SiN layer, and bottom-SiO2/Si-substrate interface. These hydrogen atoms decreased in number with annealing (1000 °C, 60 s) and spike annealing (1000 °C, about 1 s). However, when a SiN cap layer with hydrogen atoms was formed on a poly-Si/ONO film structure, hydrogen atoms in the ONO film did not decrease in number with spike annealing. It was considered that the SiN cap layer mainly performed a supply source of hydrogen into the ONO film during spike annealing, and that hydrogen atoms interdiffused between the SiN cap layer and the SiN layer of the ONO film. These results indicate that the amount of hydrogen in the ONO film can be controlled by annealing and the formation of a SiN cap layer.