Kenichi Fujii

Excitation wavelength dependence of terahertz emission from semiconductor surface

The authors have measured terahertz radiation from InSb, InAs, and InGaAs excited by femtosecond optical pulses at wavelengths of 1560, 1050, and 780nm. The amplitude of the terahertz field strongly depends on the pump wavelengths. Among the materials, the InSb emitter shows the largest terahertz emission amplitude at high power 1560nm excitation, whereas 780nm excitation provides the weakest. With increasing photon energy, the increase in emission amplitude from InAs is less as compared to that from InGaAs. The decrease from InSb and InAs originates in low mobilities of L or X valley carriers generated by intervalley scatterings.

Time-resolved analysis of infrared plasma absorption due to electron-hole-drop in germanium

Abstract By way of time-resolved analysis of the infrared plasma absorption, the decay profile of the electron-hole-drop in germanium is examined for the temperature range 1.8-4.2 K with the help of an H 2 O laser. In this temperature range, the time decay in absorption intensity is found exponential as long as 80 μsec after photoexcitation. The observed temperature dependence of the decay time can be explained by the evaporation theory. It has been necessary, however, to introduce a temperature dependent term into the work function in the manner like Φ = (14 ± 1) + (0.5 ± 0.2) T 2 K.

Far-Infrared Resonant Faraday Effect in Semiconductors

We have studied resonant Faraday effect (RFE) related to the intraband transitions in various semiconductors at low temperature through direct measurements for the Faraday rotation angle and ellipticity of the probe far-infrared (FIR) light. Through cyclotron resonance due to electrons in a thin n-InSb sample and two-dimensional electrons in the interface of GaAs/AlGaAs as well as the impurity absorption by donors in the n-InSb, we have made clear that RFE is dominated by the off-diagonal components of dielectric tensor. Experimental results for bulk n-InSb samples with various thicknesses have revealed a lot of properties of RFE as saturation effect on absorption. The oscillatory spectra induced by several twirls of the polarization plane have been observed in the extremely thick InSb sample. Spectra of the thick n-InSb also show high sensitivity of ellipticity for interference of circularly polarized lights. Besides, making use of the characteristic behavior on RFE, we can classify absorption lines due ...

Process techniques of 15-inch full-color high-resolution liquid crystal displays addressed by a-Si thin film transistors

A 15 inch-diagonal-size full-color liquid crystal display (LCD) with 1152(×3)×900 pixels has been fabricated which enables a portable workstation with improved display performances. The process techniques used for this development are described, with special reference to metallization and dry etching. In multilevel metallization, Cr/Al interconnection is metallurgically undesirable. By contrast, the Cr/Ti/Al metal system provides excellent properties of contact resistivity and thermodynamical stability. Dry etching processes are developed for multilayered insulating films and metallization-related bilayers, namely SiO2/TaOx/SiNx/(i/n+)a-Si and a-Si/Ti, respectively. Fine patterning and easier stepcoverage of subsequently deposited layers are achieved.

A study on nitric oxide formation in turbulent diffusion flames

Characteristics of nitric oxide (NO) formation in turbulent diffusion flames of hydrogen and propane in air are investigated experimentally and the potential of the Zeldovich mechanism for predicting NO formation is examined. It is observed that NO is likely to form in the narrow region corresponding approximately to the flame front where the gas temperature is maximum and in the region not far from the fuel nozzle. The NO formation rate estimated from the experiments is compared with calculated results applying the well-known extended Zeldovich mechanism. It is pointed out that the NO formation rate cannot be predicted by the Zeldovich mechanism for hydrogen and propane diffusion flames if the assumption of the equilibrated oxygen atom is applied. Kinetic calculations, including 35 elementary reactions in H−O−N system, reveal that the concentration of excess oxygen atom remains high as long as fresh hydrogen and air are continuously mixed with each other, and that such a non-equilibrium oxygen atom concentration is somewhat insensitive to the temperature level. Based on the above behavior, the NO formation rate and its temperature dependence may be predicted for hydrogen flames if the oxygen atom overshoot is taken into account. For propane flames, the NO formation rate seems too fast and its temperature dependence is too low to be explained by the Zeldovich mechanism, especially for relatively low temperature flames.

Determination of Rashba spin splitting in InxGa1−xAs/InyAl1−yAs by far-infrared magneto-optical absorption

Abstract Far-infrared magneto-optical absorption measurements of InGaAs/InAlAs heterostructures were carried out to determine a zero-field spin splitting. Peak splitting due to the zero-field spin splitting can be observed in a modulation absorption signal under pulsed electric field excitation or photoexcitation. Zero-field spin splitting is found to be 9~meV in the sample.

Far-Infrared Magneto-Optical Study of Photoexcited Indium Antimonide. I. General Characteristics

Time-resolved far-infrared cyclotron resonance was carried out at liquid helium temperatures for both n- and p-type InSb under intrinsic photoexcitation. The optically hot nature shows up very clearly for the photoelectron system. Detailed electron temperature analysis was carried out on a p-type sample, using the intensity ratio of the two lowest cyclotron transition signals. The electron temperature was found to decrease from 40 K at a time constant of 6.5 µs. Joint observation of electron and hole signals at four different wavelengths enabled us, using the calculation by Pidgeon and Brown, to modify the values of the Luttinger parameters of the valence band. Cyclotron emission similar to that detected under electrical excitation was observed in an n-type sample.

Magnetooptical Properties of MnBi Films Prepared by lonized-Cluster Beam Deposition Technique

Ionized-Cluster Beam (ICB) deposition technique developed by the authors was successfully used to prepare a ferromagnetic MnBi for magnetooptical memory applications. The film deposited simultaneously Mn and Bi onto a glass substrate by the technique, followed by annealing at 300°C for 3 hr was entirely uniform over the large substrate area, and showed a high stability in the thermal writing over a number of cycles. The nucleation and crystal growing processes of the films formed by the method were studied, and it was found that the crystal growth of MnBi starts at the annealing temperature as low as 100°C, which is nearly 1/3 of the corresponding temperature in the conventional vacuum evaporation. These results are interpreted as due to the charged particles and their kinetic energies.

Nitric oxide formation and carbon monoxide decay in the post-reaction zone of a premixed propane — air flat burner flame

Concentrations of the combustion products, especially carbon monoxide and nitric oxide, from a propane — air premixed flat burner flame were measured along the gas stream beyond the flame, and the results were examined in conjunction with chemical-kinetic calculations. It was concluded that the formation and stabilizing (with fall of temperature) of nitric oxide in stoichiometric or fuel-lean flames can be predicted by two reactions, O + N2 = NO + N and N + O2 = NO + O, and that the relative discrepancy between kinetic and simplified-partial-equilibrium models near the flame decreases downstream. For fuel-rich flames, very rapid nitric oxide formation was observed in the reaction zone; this cannot readily be explained by the above reactions in the post-reaction zone even if oxygen-atom ‘overshoot’ is taken into account. For example, at equivalence ratio f = 1.4, the necessary oxygen-atom concentration in the reaction zone would be more than 3000 times the chemical equilibrium concentration. Some reactions other than the above may need to be taken into account. The excess concentration of carbon monoxide observed just beyond the fuel-lean flame disappears rapidly along the gas flow, within about 3 ms. Its decay rate is considered to be dependent on a recombination reaction, H + OH + M = H2O + M, while the conversion reaction, CO + OH = CO2 + H, is so rapid that it can be presumed to be in partial equilibrium immediately after the flame.

Theoretical evaluation of carbon monoxide and hydrocarbon reduction by secondary-air injection

In order to evaluate the effects of various factors upon the performance of a thermal reactor with secondary-air injection which reduces carbon monoxide (CO) and hydrocarbon emitted from combustion engines, analytical studies were carried out for a model in which one-dimensional flow of gas is assumed. Effects of factors such as gas temperature, injection rate of secondary air, residence time and air/fuel ratio of the engine have been examined by chemical kinetics, taking 20 chemical species and 52 elementary reactions into consideration. The oxidation rate of CO and methane (CH4) becomes high when the gas temperature after air injection exceeds about 900 K. For a given gas temperature, there exists an appropriate range for the quantity of injection air in which CO, CH4 and formaldehyde can be reduced effectively. This range can be widened by either raising the gas temperature or prolonging the residence time. By increasing the air/fuel ratio of the engine, CO and CH4 emitted from the reactor tend to decrease. These results explain reasonably well the phenomena formerly observed experimentally.