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We have investigated the chemical and electrical properties of a thin SiO2/TiO2 stacking layer deposited on n-Si and heavily phosphorus-doped n++ Si substrates to elucidate effects of phosphorus doping of Si absorbers on the band alignment and electrical performance of a SiO2/TiO2 stack-based electron-selective contact deposited on the differently doped Si substrates. From our XPS study, we show a shift of the TiO2 energy levels up to ∼0.13 eV with respect to those of Si as the doping level of Si substrates changes. We also show that the conduction band offset of the SiO2/TiO2 stacking layer at the interface with the n++ Si substrate seems to smaller than that of the SiO2/TiO2 stacking layer at the interface with n-Si substrate. Finally, from our electrical transport measurements, we could conclude that the thinner tunneling barrier, the increased electron density in front of the SiO2 layer in the n++ Si surface, and/or the reduced barrier height by heavy doping, seem to enhance the majority electron transport property of the SiO2/TiO2/n++ Si samples compared to that of the SiO2/TiO2/n-Si samples.
The spherical wave theory of X-ray Pendellosung fringes in perfect crystals (N. Kato, Acta Cryst, 14: 526, 627, 1961) is extended to the case of crystals including a single stacking fault in an arbitrary way, Kelvin's stationary phase method is used extensively. The stationary phase condition gives us the trajectories of X-ray beams in the crystal. The phase and the amplitude along each trajectory are obtained by straightforward calculation. Based on this crystal wave field, the section patterns in X-ray diffraction topographs are obtained both for the direct and the Braggreflected waves. Characteristic fringe-patterns are expected. Through the image of a fault plane in a single section pattern, the geometrical configuration inside the crystal and the magnitude of the fault vector can be determined. Traverse patterns are also discussed. The fault image based on the plane wave theory (Whelan and Hirsch, Phil. Mag. 2: 1121, 1303, 1957) is also reformulated in the most general Laue case without the use of ad hoc assumptions on the shape of the dispersion surface.
The impact of the Al and Ge ratio in the Al-Ge pastes are investigated for fabricating the single crystalline Si1-xGex thick layers on large area Si substrates by screen-printing metallization process. From X-ray reciprocal space maps, Ge fraction in the fabricated Si1-xGex thick layers are found to increase up to 40% with increasing the Ge ratio in the Al-Ge pastes. On the other hand, the interface of the Si and Si1-xGex layers are getting winding with increasing the Ge ratio in the Al-Ge pastes. The Al-Si-Ge phase diagram indicated that uniform SiGe layer can be fabricated by adjusting the Al-Ge ratio in the pastes within the liquid phase region.
κ-Al2O3-type GaFeO3 is a promising multiferroic material due to the coexistence of a large spontaneous magnetization and polarization near room temperature. In the current study, we present the magnetic properties of single crystalline GaFeO3 and compare it with that of ε-Fe2O3. Magnetic measurements revealed that spontaneous magnetization appears below 540 K in two steps, similar to that reported for ε−Fe2O3. Partial magnetic ordering takes place at 540 K (TN1), with Fe3+ ions in two distorted octahedral sites ordering antiparallel to one another. Upon further cooling at 200 K (TN2), the remaining Fe3+ ions in regular octahedra and tetrahedra order antiparallel to one another. Substitution of Ga for Fe in ε-Fe2O3 leads to a decrease in TN1 and TN2 from 850 to 540 K and from 480 to 200 K, respectively, caused by a dilution of magnetic Fe by nonmagnetic Ga and preferential site occupation of Ga.
A novel preparation method of B-doped p-type BaSi2 (p-BaSi2) is proposed to realize heterojunction crystalline Si solar cells with p-BaSi2. The method consists of thermal evaporation of BaSi2 on B-doped amorphous Si (a-Si). In this study, the effect of a-Si interlayers and substrate temperature during BaSi2 evaporation on the electrical characteristics and crystalline quality of the evaporated films were investigated. While no cracks were found in the BaSi2 films formed using hydrogenated a-Si deposited by plasma enhanced chemical vapor deposition (PECVD), the films formed with sputtered a-Si have cracks. In addition, BaSi2 films formed with a 600 °C substrate temperature using PECVD a-Si showed p-type characteristics. After a post-deposition anneal at 800 °C for 5 minutes, the film hole density was measured at 1.3×1019 cm-3 and boron was found to be uniformly distributed throughout the film. These results show that the proposed method using PECVD is promising to obtain p-BaSi2 thin films with high hole density for p-BaSi2/n-type crystalline Si heterojunction solar cells.
To improve conversion efficiency of silicon nanowire (SiNW) solar cells, it is very important to reduce the surface recombination rate on the surface of SiNWs, since SiNWs have a large surface area. We tried to cover SiNWs with aluminum oxide (Al2O3) and titanium oxide (TiO2) by atomic layer deposition (ALD), since Al2O3 grown by ALD provides an excellent level of surface passivation on silicon wafers and TiO2 has a higher refractive index than Al2O3, leading to the reduction of surface reflectance. The effective minority carrier lifetime in SiNW arrays embedded in a TiO2/Al2O3 stack layer of 94 μsec was obtained, which was comparable to an Al2O3 single layer. The surface reflectance of SiNW solar cells was drastically decreased below around 5% in all of the wavelength range using the Al2O3/TiO2/Al2O3 stack layer. Heterojunction SiNW solar cells with the structure of ITO/p-type hydrogenated amorphous silicon (a-Si:H)/n-type SiNWs embedded in Al2O3 and TiO2 stack layer for passivation/n-type a-Si:H/back electrode was fabricated, and a typical rectifying property and open-circuit voltage of 356 mV were successfully obtained.
Thermal evaporation is a simple method to fabricate a BaSi2 film, a new solar cell material consisting of earth-abundant elements. In this study, we optimized the evaporation process and suppressed near-interface oxidation in evaporated BaSi2 films on Si(100) substrates, which has been detected in previous studies. Composition depth profiles determined by Auger electron spectroscopy show the decrease of oxygen concentration near the interface to the background level by optimizing the source pre-melting condition. By reducing oxygen concentration, the BaSi2 film becomes more preferentially oriented toward  as long as the deposition rate is not changed, as evidenced by X-ray diffraction. It is also shown that the rectification behavior of n-BaSi2/p+-Si diodes improves by suppressing the near-interface oxidation.
We developed a new GaN on SiC growth method by metalorganic vapour phase epitaxy (MOVPE) using of a single 2-dimension-growth step. Prior to epitaxy, to inhibit pre-reaction of Si-face SiC substrate with TMGa and NH3, TMAl was flowed without NH3. 1.5 μm of undoped crack-free GaN was grown on 6H-SiC (Si-face). Without buffer layer, the vertical resistance of GaN/SiC structure was found to be around 82.1Ω as determined by I-V characteristic. Further reduction in vertical resistance is expected by growth of n-GaN (1.5μm)/SiC structure (300μm). We also expect a SiC-based GaN heterostructure vertical FET will achieve high power and high switching speed performance.
The local strain field and the intermixing of a Ge nano-islands (NIs)/Si spacer stacked structure in a novel solar cell with a p-i-n type Si single crystal with two-dimensional photonic nanocrystals connecting to the vertically aligned NIs were analyzed using electron microscopy. High-angle annular dark field-scanning transmission electron microscope (HAADF-STEM) images show intermixing between Ge and Si clearly and reveal that the surface segregation of Ge becomes advanced. The average composition of the NIs is Ge0.42Si0.58, which is almost constant in a row of vertically aligned NIs. The local strain analysis results obtained from the high-resolution transmission electron microscope (HRTEM) images show that the strain state is partially relaxed after the elastic relaxation of NIs.
Milk is an effective post-exercise rehydration drink that maintains the net positive fluid balance. However, it is unclear which components are responsible for this effect. We assessed the effect of milk protein solution (MPS) obtained by dialysis on body fluid retention. Milk, MPS, milk electrolyte solution (MES), sports drink and water were administered to male Wistar rats at a dose of 6 ml/rat after treadmill exercise. Total body fluid retention was assessed by urine volume 4 h after administration of hydrating liquids. The rate of gastric emptying was evaluated by a tracer method using 13C-labelled acetate. Plasma osmolality, Na and K levels, and urinary Na and K were measured by HPLC and osmometry, respectively. The gastric emptying rate was not delayed by MPS. During 4 h of rehydration, cumulative urine volumes differed significantly between treatment groups (P < 0·05) with 4·9, 2·2 and 3·4 ml from water-, milk- and MPS-fed rats, respectively. Thus, MPS elicited 50 % of the total body fluid retention of milk. Plasma aldosterone levels were significantly higher in MPS- and milk-fed rats compared with water-fed rats. Plasma osmolality was maintained at higher levels in MPS-fed rats than in water- and MES-fed rats (P < 0·05). Cumulative urine Na excretion was also suppressed in the milk- and MPS-fed groups compared with the MES-fed group. Our results demonstrate that MPS obtained by dialysis clearly affects net body water balance without affecting gastric emptying after exercise. This effect was attributed to retention of Na and water, and maintenance of plasma osmolality.
Effects of rapid thermal annealing (RTA) with a SiNx encapsulant on molecular beam epitaxial GaAs are studied with deep level transient spectroscopy (DLTS) measurements and x-ray photoelectron spectroscopy (XPS) measurements. The RTA was performed at various temperatures form 800°C to 1100°C for 6sec. The electron trap EL2 is produced by the RTA above 850°C The EL2 depth profile produced after the RTA is fitted with a complementary error function. The SiNx cap layer is more effective to prevent the formation of the EL2 than the SiO* cap layer during the RTA, because the critical temperature of the SiNx cap where the EL2 concentration starts to increase is higher than that of the SiOx cap. Slight increase of the oxidized Ga atoms is observed after the RTA near the cap surface. The enhancement of the EL2 trap is discussed considering the outdiffusion of Ga atoms into the cap layer during the RTA.
In this study, we evaluate the electrical characteristics of the silicon on insulator (SOI) layer made by the wafer bonding method using a photoconductivity modulation method, in other words, noncontact laser beam induced conductivity/current (LBIC) method. The He-Ne laser pulse (λ= 633nm, pulse width=2ms) is used as the carrier-injection light source.
The detected signal intensity decreases at the void area as compared with at the center area of the SOI layer where there are no voids. The positions of the voids revealed by the proposed method are in good agreement with those by X-ray topography. We also measure the lifetime using the photoconductivity decay method using the laser diode. The lifetime at the void area is much shorter than that at the center area. It is considered that the decrease in the detected signal intensity at the void area is due to reduction in the minority carrier lifetime.
Silicon-on-insulator films fabricated by the wafer bonding technique were studied with capacitance-voltage (c-V) and deep-level transient spectroscopy (DLTS) measurements. For our experiments, two kinds of SOI wafers were prepared. Many voids were present in one sample (void sample), but few voids were in the other sample (no void sample). Before annealing, two DLTS peaks (E-0.48 eV and Ec-0.38 eV) were observed in the SOI layer of the void sample. For the no void sample, different two DLTS peaks (Ec-0.16 eV and Ec-0.12 eV) were observed. The trap with an activation energy of 0.48 eV was annealed out after 450 °C annealing for 24 h. On the other hand, other traps were annealed out after 450 °C annealing for several hours. During annealing at 450 °C, thermal donors (TDs) were formed simultaneously. In usual CZ sil icon, a DLTS peak of TD was observed around 60 K. In the no void sample, however, a TD peak was observed at a temperature lower than 30 K. This TD was annihilated by rapid thermal annealing. This suggests that the TD with a shallower level was formed in the no void sample after annealing at 450 °C.
We describe physics and control of Si/SiGe heterointerfaces. A clear distinction will be made between the vertical and lateral effects of the Si/SiGe interface from the viewpoint of interface engineering. Ge surface segregation during nonequilibrium MBE growth and surfactant-mediated-growth are highlighted as prominent examples for the vertical effects while interface microroughness is addressed for the lateral effects. The influence of the interface effects on radiative recombination of indirect excitons is described in the context of SiGe-based optoelectronic applications.
A multi-hierarchy simulation model aiming magnetic reconnection studies is developed and improved in which macroscopic and microscopic physics are computed consistently and simultaneously. Macroscopic physics is solved by mag-netohydrodynamics (MHD) algorithm, while microscopic dynamics is expressed by particle-in-cell (PIC) algorithm. The multi-hierarchy model relies on the domain decomposition method, and macro- and micro-hierarchies are interlocked smoothly by hand-shake scheme. As examination, plasma flow injection is simulated in the multi-hierarchy model. It is observed that plasmas flow from a macro-hierarchy to a micro-hierarchy across the magnetic field smoothly and continuously.
This paper reports on a new bottom-up technique of forming silicon nanostructures based on natural aggregation of nanocrystalline (nc) -Si dots in the solution. We first study how the nc-Si dots deposited on the Si substrate get mobile in the solution by simply dipping the substrate with the nc-Si dots on into various solutions. We then demonstrate a solution droplet evaporation method that utilizes aggregation of the dots when we evaporate a solution droplet applied onto the nc-Si dots randomly deposited on the Si substrate. It is shown that the nc-Si dots are assembled well in a droplet of the hydrofluoric acid solution, resulting in various regular patterns on the substrate.
The slip lines introduced in Si wafers during rapid thermal processing (RTP) were revealed with focused reflectance microwave probe (RMP) method. The signal intensity of RMP which is related to optically injected excess carrier concentration decreases at slip lines. The region in which the signal intensity decreased is in good agreement with results of X-ray topography and theoretical analysis considering thermal stress caused by temperature drop at the wafer periphery during RTP. According these results, it is considered that carrier lifetime is decreased by slip dislocations which are effective recombination centers.
Variations of thermal donors (TDs) in highly phosphorus-diffused n-type silicon wafers (diffused wafer) have been studied with deep-level transient spectroscopy and capacitance-voltage measurements. The introduction and annihilation of TDs have been performed with heat treatment at 450°C and rapid thermal annealing (RTA) in the temperature range 600-900°C,respectively. In diffused floating zone-grown (FZ) silicon wafer, TDs were observed. It is thought that oxygen diffuses into FZ silicon during the diffusion process, since no TDs are generally formed in FZ silicon for the low oxygen concentration. The behavior of TDs in diffused wafer corresponded with that in oxygen-rich bulk silicon. TDs were completely annihilated by RTA at 700 and 800°C for the as-diffused wafers and the heat-treated ones at 450°C for 24 h, respectively, and the annihilation rate for the as-diffused wafers was fast, as compare to that for the heat-treated ones. This results may be caused by difference in the total concentration and cluster size of TDs.