Tetsuo Muranoi

Properties of stannic oxide thin films produced from the SnCl4-H2O and SnCl4-H2O2 reaction systems

Abstract Transparent and conductive stannic oxide films were produced at the relatively low temperature of 250°C from the SnCl4-H2O and SnCl4-H2O2 reaction systems by a chemical vapour deposition method. The films were not doped with impurities. Films formed from the first system are superior to those formed from the second with respect to electrical properties although they have a lower deposition rate at the same deposition temperature. The former system gives rise to films with resistivities in the range 10–10-3 Ω cm between 250 and 400°C. The latter system produces films with resistivities in the range 102–10-2 Ω cm between 250 and 450°C. The electrical properties depend on the absorption of hydrogen peroxide as well as on the grain size, which depends on the deposition temperature and the reaction system. The spectral transmissivity for films 0.36–1.1 μm thick varies over the range 80–95% in the regions between 400 and 650 nm for both systems. Different reaction mechanisms take place in different temperature regions for both systems since there are two activation energies in the plot of deposition rate as a function of temperature.

A novel magnetic contact duplication technique for servo writing on magnetic disks

A novel magnetic contact duplication technique is proposed in order to write a servo signal on hard disks and floppy disks at a high speed and a low cost. In this technique a magnetic layer of a master disk is lithographically patterned in accordance with a servo signal, having low coercivity, and dc magnetic field is applied to a slave disk contacted with the master one. A computer simulation using finite element method shows that the pattern of the master disk can be duplicated on a slave. The possibility of duplication by using this technique is confirmed from experimental results in which a Bitter pattern of a duplicated slave medium is clearly observed.

Magnetization patterns of slave media duplicated by using patterned master media

It is possible that a servo signal can be written on hard and floppy disks at high speed and low cost by using a magnetic contact duplication technique with patterned master media. The duplicated magnetization patterns of the slave media is elucidated. The duplicated magnetization is not only reversed at transitions, but also changes between transitions for bit lengths more than several μm, while the magnetization is reversed at transitions, and is almost uniform between transitions for bit lengths less than several μm. Therefore, when the above-mentioned duplication technique is applied to hard and floppy disks, it is expected that the magnetization changes only at transitions.

The electrical properties and impurity profiles of ZnSe films on GaAs and of Gallium-diffused ZnSe single crystals

Abstract The electrical properties and impurity profiles of ZnSe films and gallium-diffused ZnSe single crystals were investigated. ZnSe films 10–30 μm thick were epitaxially grown on p-type GaAs in the vapour phase by using metallic zinc and metallic selenium without intentional doping. Low resistivity films (of the order of several ohm centimetres) were deposited, even in the presence of excess selenium, at temperatures above 650°C. The carrier concentration profile showed an exponential dependence on the distance from the interface. Donor and acceptor concentrations of about 10 18 cm -3 and a compensation ratio close to unity were obtained. An electron probe microanalyser was used to determine the impurity profiles on the cleaved surfaces. Gallium and arsenic atoms were distributed exponentially throughout the ZnSe films with concentrations of the order of 10 20 cm -3 . The gallium concentration was always higher than the arsenic concentration. The concentration of the electrically active impurity was about two orders of magnitude less than the gallium and arsenic concentrations. The gallium-diffused ZnSe was prepared in an evacuated quartz ampoule by diffusing gallium from the melt into a melt-grown ZnSe single crystal in order to compare the electrical properties of gallium-diffused and undiffused ZnSe. The resistivity of the gallium-diffused ZnSe was also low. We conclude from these results that the resistivity of ZnSe on GaAs became low because of gallium auto-doping. The gallium concentration profile in the bulk ZnSe was described by a complementary error function in contrast with the exponential distribution obtained for ZnSe films on GaAs. A trial solar cell of dimensions 4 mm x 4 mm had an open-circuit voltage of 0.65–0.75 V and a short-circuit current of 0.9–2.2 mA.

Vapor Phase Epitaxial Growth of Highly Conductive P -Type ZnSe Films with Codoping of P and Li

Highly conductive p-type ZnSe films were grown at 450–500°C onto (100)GaAs by vapor phase epitaxy with codoping of P and Li. Vapors of Zn, Se and impurities were transported separately to the vicinity of the substrates. Hall effect measurement revealed that p-type films were degenerate. When either only P or Li was doped, the resistivity was very high and its conductivity type was unknown. The SIMS analysis showed a uniform profile of both impurities in the p-type epitaxial film: the Li concentration was estimated as 1019 cm-3; P was an order of 1018 cm-3 with the aid of EPMA.

Vapor and Solid Phase Epitaxies of ZnSe Films on (100)GaAs Using Metallic Zn and Se

Low temperature growth of ZnSe layers on (100)GaAs substrates has been performed from the vapor phase using metallic Zn and metallic Se as source materials. Before deposition, the substrate was thermally etched in an H2 flow at 500 or 550°C for 5 min. Epitaxial growth was successful above 230°C. An activation energy of 10 kcal/mol was obtained for the deposition process. Films grown at 400°C showed low resistivity (on the order of 1 Ωcm) when the flow rates of Zn and Se were almost the same. Solid phase epitaxy (SPE) occurred at 400°C for the micro-crystalline films deposited at 180–220°C on a thermally etched substrate.

Gas effect on transport rates of ZnSe in closed ampoules

Abstract Gas effects on the transport rates of ZnSe in closed systems were investigated. An ampoule (10 mm × 90 mm) was fabricated from a quartz tube which had been cleaned in a hydrogen flow at about 1000°C for 5 hours. The source material was polycrystalline ZnSe of 6N purity with about a 3 to 6 mm particle size. Ar, H 2 or He gas was introduced under pressure p , along with the source. The ampoule was sealed and placed in an electric furnace for 15 hours. The source temperature was 1069°C, and the growth end temperature was 1048°C. Here, the transport rate was defined as J. J argon started to decrease at p argon = 9 Torr, J hydrogen decreased at p hydrogen = 45 Torr, and J helium was almost constant in all over the p helium range. The thermal conductivity of helium is almost 10 times that of argon gas, but similar to that of hydrogen gas. It was considered that J hydrogen was intermediate between J helium and J argon since hydrogen is a reactive gas. It was concluded that J argon and J hydrogen had a diffusion limited mass transport region.

Effects of Anthracene Doping on Electrical and Light-Emitting Behavior of 8-Hydroxyquinoline-Aluminum-Based Electroluminescent Devices

Organic electroluminescent (EL) cells consisting of an anthracene-doped 8-hydroxyquinoline aluminum light-emitting layer and a hole transport layer were prepared by co-evaporation, and their electrical and light-emitting behavior was examined. It was confirmed that anthracene doping increased the available current density of the EL cells and EL efficiency, which caused an increase in EL brightness. However, the EL spectrum was only slightly affected by the anthracene doping.

Low Temperature Vapor Phase Epitaxy of Undoped ZnSe Films on (100) GaAs Using Metallic Zn and Se

High-quality ZnSe films were grown at 290°C by VPE with an improved reaction apparatus: a reflection plate for Se vapor was prepared at the end of the nozzle. With this configuration, the growth rate became several times higher than that without such a plate. Exciton emissions including free exciton line were predominant. The deep level emission was very low even at RT in the PL spectrum. The electron mobility was 2410 cm2/Vs at 77 K.

Micromagnetic calculation of the magnetization process in nanocontacts

We report herein the micromagnetic calculations of the magnetic domain walls in nanoconstrictions of various shapes for H-shaped samples and estimate the domain wall widths. The length and width of the nanoconstriction and the exchange stiffness constant in the nanoconstriction was varied for each case. In the case of a uniform exchange stiffness constant at the nanoconstriction, the domain wall width depends on the length and width of the nanoconstriction. Each domain wall width D calculated herein is longer than the constriction length L, and the exchange stiffness constant is 1.05×10−6erg∕cm. The small exchange stiffness at the nanoconstriction leads to the small domain wall width. These results imply the possibility of the large domain wall scattering only for nanoconstrictions with a small effective exchange coupling between the two magnetic materials.