Jiro Yamaguchi

Ferroelectric Properties of RF Sputtered PLZT Thin Film

A series of technical data for the preparation of ferroelectric thin film PLZT by RF sputtering at substrate temperatures lower than 400°C with subsequent annealing is described. Films with dielectric and optical properties of considerable quality have been obtained under certain conditions. Parametric changes in the dielectric, optical and pyroelectric properties according to sputtering, annealing conditions and film thickness have also been clarified. The dielectric properties depend heavily on film thickness. Well-annealed thick films have dielectric constants nearly equal to those of ceramics. Discussion on the thickness dependence of dielectric properties and on the effects of the packing density of PLZT and other preparation conditions is made.

Preparation of PbTiO3 Ferroelectric Thin Film by Chemical Vapor Deposition

Chemical vapor deposition of PbTiO3 thin film on the substrate of Pt plate has been successfully made. (100)- and (001)-oriented PbTiO3 film has been obtained under a certain deposition condition. Surface of the film is smoother and the deposition rate of 8.3 µm/h is much higher, as compared with those of conventional sputtering method.

Electric Conduction through Thin Insulating Langmuir Film

Electric conduction through calcium stearate Langmuir films of several monomolecular layers has been studied. The devices are prepared by transferring monolayers of stearic acid spread on an aqueous surface to an evaporated tin electrode on a glass substrate and evaporating the upper electrode. Tunnel emission is observed when the aluminum upper electrode is negatively biased and Schottky emission is observed when the lower electrode is negatively biased. The trapezoidal energy barrier model of Simmons adequately accounts for the details of current‐voltage‐temperature characteristics. The observed barrier height at the stearate and tin interface is 0.8 ev and that at the stearate and aluminum interface is 1.3 ev.

Photoconductivity of Copper Phthalocyanine Single Crystals

Dark conductivity and photoconductivity of copper Phthalocyanine single crystals of the β form are measured as a function of electric field strength, temperature and light intensity in vacuum and in the atmosphere of H 2 , O 2 and Ar. The spectral responces of photocurrent and optical absorption are also measured in the atmosphere of H 2 . The conductivity of a copper phthalocyanine single crystal is 1×10 -11 Ω -1 cm -1 at 100°C and the activation energy of dark current is 1.96±0.05 eV in the measured range of 30°C to 250°C, while that of photocurrent is 0.41±0.03 eV in the measured range from 30°C to 200°C. The photocurrent generated by continuous illumination depends on the square root of light intensity and that generated by flash illumination of Q switched ruby laser light decays via bimolecular recombination. The photocurrent per quantum of incident light appears to vary with wave length in the same way as the absorption coefficient. These results are consistent with the scheme that photocarriers are...

Ge-Si n-n Heterojunctions

Ge-Si n-n heterojunctions have been fabricated by epitaxial vapour growth process of hydrogen reduction of germanium tetrachloride. They have a good rectification property and a short switching time less than a few nano-seconds. In the junction there exists a double Schottky barrier due to interface states, which capture electrons more than 1.5×1013 cm-2 as acceptor-like states. The voltage-current characteristics have been measured at temperatures between 77°K and 300°K. In the low voltage region of easy flow direction (Germanium positively biased), d(log I)/dV is independent of temperature, but in the higher voltage region it is proportional to q/kT. The reverse characteristics (Germanium negatively biased) are divided into three separate regions, which are I∝V0.7~0.8, I∝V3/2 and I∝exp (BV) in the order of magnitude of reverse bias voltage, where B is a constant depending on temperature and donor concentration of silicon. The conduction mechanisms of this heterojunction have been discussed qualitatively.

Electrical Conduction in Germanium Grain Boundary Plane

The reduced resistivity and Hall coefficient on the grain boundary in n type germanium bicrystal have been measured over the temperature range about 2.8~300°K, and the dislocation acceptor level and carrier density in the grain boundary are determined. Experimental results show that the temperature dependence of the mobility may be divided into three regions: In the region of 80~300°K and 20~80°K, the mobility µ may be expressed as normal band conduction by the form µ-1=µls-1+µi-1+µd-1, where the suffices ls, i and d express the contributions to the scattering from the space charge potential well due to the grain boundary, ionized impurities and dislocation, respectively. In particular, the temperature dependence of µd agrees quantitatively with Dexter and Seitzs theory as a function of dislocation line density. In the low temperature region of 2.8~25°K, a large and oscillatory negative magnetoresistance is observed and the temperature dependences of reduced Hall coefficient and resistivity have a similar tendency to impurity band conduction in highly doped single crystals.

Enhanced Carrier Diffusion Associated with the Instability in Germanium Slice

Enhanced carrier diffusion associated with the density wave instability due to the gradient of carrier density in germanium slice was estimated at 77°K from the observations of (1) the distribution of carrier density along the direction of the thickness of the slice in the transverse magnetic field and (2) the transient time necessary for the decrease of the gradient of carrier density. The results show that when the instability occurs, the ambipolar diffusion constant Da of hot carriers becomes very large, i.e., Da~105 cm2/sec (at 700 V/cm) which is larger about an order of magnitude than that before the instability occurs. The phenomenon is discussed in conjunction with the current oscillation (wherein microwave emission was also observed) in germanium slice, as well as the frequency response of the devices relative to the magnetic barrier layer effect.

Ac Conductivity of Pyrene Iodine Charge Transfer Complex

Electrical conduction of a charge transfer complex between pyrene and iodine is studied by ac method. Frequencies used are from 1.0×10 3 to 2.4×10 10 Hz at the temperature region from 80°K to 330°K. The conductivity of the complex is expressed as σ=σ d +σ ω ; σ d is independent of frequency, σ ω dependent on frequency. Above 250°K, σ d predominates and below 150°K, σ ω predominates in σ in the frequency region of the measurement. It is suggested that σ d is due to the unpaired electrons in conduction state since the activation energy of conductivity and that of spin density are the same value of 0.14 eV and the conductivity shows no frequency dispersion at the higher temperatures. σ ω is due to the localized unpaired electrons surrounded by a potential barrier of 0.07 eV and it is explained by an equation based on a simplified hopping model.

Instability Associated with the Gradient of Carrier Density in Germanium Slice

The onset of current oscillation in a germanium slice in a transverse magnetic field was studied by taking into consideration the existence of gradient of carrier density along the direction of thickness. The gradient was estimated from the observations of 9.3 Gc microwave reflection and the threshold gradient experimentally determined for the onset of the density wave instability was compared with the theoretically estimated one. The results show that this threshold gradient is nearly equal to that of the instability of fundamental mode. However, the oscillation was quenched in a high transverse magnetic field.

Effect of Heat Treatment on Electrical Conduction in DPPH Single Crystals Grown from Benzene Solution

The dependence of conduction on the concentration of Benzene contained in DPPH recrystallized from a benzene solution is reported. The concentration is varied by heat treatment of as-grown single crystals at about 63°C. The conductivity of a single crystal which contains one benzene molecule per DPPH molecule is 1.6×10 10 \(\varOmega\) -1 cm -1 . The conductivity decreases with decreasing concentration of benzene. The activation energy increases in such a way that the decrease in conductivity can be attributed to the increase in activation energy. This correlation between the activation energy and the conductivity is explained by the polarization effect of benzene by assuming that the activation energy can be expressed as E = I - A -2 P , where I , A , and P are the ionization energy, the electron affinity, and the polarization energy, respectively.