Masahiko Hasumi

Low-temperature fabrication of ultrathin ZrO2/Si structure using metal deposition followed by oxygen annealing

Metal deposition followed by oxygen annealing has been carried out for the fabrication of ZrO2/Si structures. Using this method, 200°C oxygen annealing enables the oxidation of Zr metal and 220°C annealing enables the surface potential control of Si in metal–insulator–semiconductor (MIS) structures, even if the dielectric constant of ZrO2 has been shown to be 11.8. High-quality ZrO2 films with a dielectric constant of ~20 can be achieved by 300°C annealing with an interfacial layer of 0.9 nm thickness. For these films, no degradation of leakage characteristics was observed after the thermal budget corresponding to that of impurity activation at 850°C for 30 min. Consequently, using this method, a high-quality ZrO2/Si structure that has good chemical stability under a high thermal budget could be fabricated at a low temperature.

A change of the superstructure and an associated rise of the superconducting critical temperature in the organic superconductor β-(BEDT-FFT)2I3

Abstract X-ray diffraction measurement of the superstructure were made under pressure in the title compound. The wave vector of the superstructure was found to become short below about 100 K. This change occurs even at ambient pressure when the sample is kept in the range 100–120 K for a long time, say, 24 h. The sample annealed for 65 h at ambient pressure undergoes a superconducting transition at about 7 K, which is much higher than that observed in samples cooled with a conventional speed. These results are discussed in relation to the so-called “low-Tc” and “high-Tc” states of this compound.

Multi Junction Solar Cells Stacked with Transparent and Conductive Adhesive

We propose a polyimide transparent adhesive layer dispersed with In2O3–SnO2 (ITO) conductive particles (polyimide-ITO) to be used in the mechanical stacking of solar cells. A 20-µm-thick polyimide-ITO layer had a high transmissivity from 78 to 80% for wavelengths ranging from 500 to 1000 nm and a low connecting resistivity of 2.3 Ω cm2 at minimum. The fabrication of stacked cell consisting of a top hydrogenated amorphous silicon (a-Si:H) p–i–n cell and a bottom hetero-junction with an intrinsic thin-layer (HIT)-type silicon cell was demonstrated using an intermediate polyimide-ITO layer. A high open circuit voltage of 1.34 V was experimentally obtained. Simultaneous electric power generation from the top and bottom solar cells was achieved.

Dimensionality of the Superconductivity in YBa2Cu3O7-δ

Superconducting fluctuation-induced diamagnetism was observed in YBa 2 Cu 3 O 7-δ with different oxygen deficiencies. In a slightly deficient sample, the fluctuation is small and exhibits the temperature dependence of a three-dimensional nature. With increasing defects, however, the fluctuations were found to be enhanced and exhibit a crossover from three- to two-dimensional behaviors at higher temperatures. The dimensionality, which is controlled by the interlayer coupling between the CuO 2 planes, is very sensitive to oxygen deficiency in the CuO chains, even when the critical temperature remains around 90 K.

Antiferromagnetic Transition in Y2BaCuO5

Magnetism of a compound Y2BaCuO5 has been investigated by means of electron paramagnetic resonance (EPR) and static susceptibility measurements. An EPR absorption signal due to Cu2+ was observed. The temperature dependence of the integrated signal intensity follows a Curie-Weiss law, consistent with the results of static susceptibility. The Weiss temperature is -33±2 K. The EPR signal becomes appreciably broadened at low temperatures and disappears at about 20 K. This is indicative of an antiferromagnetic transition. A peak of static susceptibility is observed at 14 K.

Investigation of Silicon Surface Passivation by Microwave Annealing Using Multiple-Wavelength Light-Induced Carrier Lifetime Measurement

A simple annealing method using a commercial 2.45 GHz microwave oven is reported to increase the minority carrier lifetime ?eff for 4-in.-size 500-?m-thick 20 ? cm n-type silicon substrates coated with 100-nm-thermally grown SiO2 layers. The microwave annealing was conducted with 2-mm-thick glass substrates, which sandwiched a silicon sample to maintain the thermal energy in silicon and realize gradual cooling. A 9.35 GHz microwave transmittance measurement system was used to measure ?eff in the cases of continuous-wave 635 and 980 nm laser diode (LD) light illuminations. Radio-frequency Ar plasma irradiation at 50 W for 60 s to the top surface of a silicon sample markedly decreased ?eff in the range from 6.0?10-6 to 2.4?10-5 s and from 4.2?10-5 to 6.4?10-5 s in the cases of 635 and 980 nm light illuminations, respectively, while ?eff had the same distribution from 1.6?10-3 to 3.1?10-3 s for the initial samples. The finite element numerical analysis revealed that Ar plasma irradiation caused high densities of recombination defect states at the silicon top surface in the range from 1.3?1013 to 5.0?1013 cm-2. Microwave annealing at 700 W for 120 s markedly increased ?eff in the range from 8.0?10-4 to 2.5?10-3 s, which were close to those of the initial samples. The density of recombination defect states was well decreased by microwave annealing to low values in the range from 7.0?1010 to 3.4?1011 cm-2. The high ?eff achieved by microwave annealing was maintained for a long time above 5000 h.

Crystalline Silicon Solar Cells with Two Different Metals

We propose crystalline silicon solar cells with Al and Au metals. P-type substrates were coated with 100-nm-thick thermally grown SiO2 layers. The top SiO2 layer was thinned to about 1.5 nm. Stripes of Al and Au were formed with a gap of 0.29 mm on the top surface in order to cause an internal built-in potential in silicon because of the difference between their work functions. Solar cell characteristics were observed by halogen lamp illumination at 21.7 mW/cm2. The short-circuit current density, open-circuit voltage, and fill factor were 5.8 mA/cm2, 0.49 V, and 0.57. The conversion efficiency was 7.5%. Photo-induced holes and electrons flowed into Au and Al electrodes, respectively, by the tunneling effect.

Activation of silicon implanted with phosphorus and boron atoms by microwave annealing with carbon powder as a heat source

We report the activation of silicon implanted with phosphorus and boron atoms by microwave annealing using carbon powder as a heat source. Silicon substrates were covered with carbon powder and then irradiated with 2.45 GHz microwaves using a commercial microwave oven. Carbon powder effectively absorbs microwaves and heats itself at 1000 °C. Silicon substrates are heated by thermal conduction. We carried out implantations of phosphorus atoms at a concentration of 1.0 × 1015 cm−2 at 75 keV and boron atoms at a concentration of 1.0 × 1015 cm−2 at 25 keV for p- and n-type silicon substrates, respectively. Microwave annealing at 1000 W for 120 s achieved sheet resistivities of 140 and 85 Ω/sq for the phosphorus- and boron-implanted samples, respectively. It also realized the recrystallization of surface amorphized regions caused by implantation. Moreover, low surface recombination velocities of 3.8 × 102 and 2.7 × 102 cm/s were obtained at the top implanted surfaces for the phosphorus- and boron-implanted samples, respectively. Typical diode rectified characteristics and solar cell characteristics with a conversion efficiency of 10.1% were successfully obtained.

HfO2/Si and HfSiO/Si Structures Fabricated by Oxidation of Metal Thin Films

Hafnium metal deposition followed by oxidation, either on bare silicon or SiO2/Si substrates, was performed for the fabrication of high-k/Si gate stacks with small equivalent oxide thickness values. HfO2/Si structures were fabricated without substrate heating but with the electron cyclotron resonance (ECR) plasma oxidation of Hf metal deposited on bare Si substrates by DC magnetron sputtering. These HfO2/Si structures have ideal abrupt interface without interfacial layer (IL)-SiO2 and silicide layers, as determined by an X-ray photoelectron spectroscopy (XPS) measurements. A direct stacking was induced by the characteristic film growth of ECR plasma in a buried interfacial region. On the other hand, on SiO2/Si substrates, the HfSiO/Si structures were successfully fabricated by thermal treatment for both the interdiffusion of Hf metal and SiO2, and the oxidation of the layer. The HfSiO/Si structures show small leakage currents because of high barrier heights and have no hafnium silicide layer.

Photo induced minority carrier annihilation at crystalline silicon surface in metal oxide semiconductor structure

We report the properties of features of photo induced minority carrier annihilation at the silicon surface in a metal–oxide–semiconductor (MOS) structure using 9.35 GHz microwave transmittance measurement. 7 Ω cm n-type 500-µm-thick crystalline silicon substrates coated with 100-nm-thick thermally grown SiO2 layers were prepared. Part of the SiO2 at the rear surface was removed. Al electrode bars were formed at the top and rear surfaces to form the structures Al/SiO2/Si/SiO2/Al and Al/SiO2/Si/Al. 635 nm light illumination onto the top surface caused photo induced carriers to be in one side of the silicon region of the Al electrode bar of the structure Al/SiO2/Si/SiO2/Al. Microwave transmittance was measured on the other side of the silicon region of the Al electrode bars. The measurement and analysis of microwave absorption by photo induced carriers laterally diffusing across the silicon region coated with Al electrodes revealed a change in the carrier recombination velocity at the silicon surface with the bias voltage applied onto the top Al electrode. The applied bias voltages of +2.0 and −2.2 V gave peaks at surface recombination velocities of 83 and 86 cm/s, respectively, for the sample structure Al/SiO2/Si/SiO2/Al, while it was 44 cm/s under the bias-free condition. A peak surface recombination velocity of 81 cm/s was only observed at a bias voltage of −2.0 V for the sample structure Al/SiO2/Si/Al.