Minoru Hagino

Crystallization and growth process of lead titanate fine particles from alkoxide-prepared powders

Lead titanate particles of controlled size around the nanometer range were prepared by hydrolyzing a mixture of the constituent metal alkoxides. The hydrolysate powder was crystallized by calcination into a tetragonally distorted perovskite structure. The hydrolysate started to crystallize by calcination at 470° C for one hour and the increase of the particle size due to the coalescence began at about 530° C. The increase continued beyond 900° C. The particle calcined at temperatures higher than 700° C seemed to become poly-crystalline. X-ray analysis shows that the strain in the particle was less than 0.2%. The smallest size of a well crystallized particle was about 15 nm.

Influence of Exposure to CO, CO2 and H2O on the Stability of GaAs Photocathodes

The influence of CO, CO2 and H2O gases on the stability of negative-electron-affinity (NEA) GaAs photocathodes during operation is investigated in the present work. We have found that exposure both to H2O and CO2 decreases the photocurrent of the photocathode. However, exposure to CO, which is known as a harmful gas to various photocathodes, has little effect on the photocathode stability. Furthermore, the effects of these gases on the restoration of the photocurrent by additional cesium deposition are investigated. These results are discussed with regard to the Cs/O activation layer which plays an important role in NEA GaAs photocathodes.

MBE growth mechanisms of ZnSe: Flux ratio and substrate temperature

Abstract The purpose of this paper is to present a new growth model to clarify the MBE growth processes of ZnSe. It is found that the relation between the growth rate and the substrate temperature calculated from our model is in quite good agreement with the measured one. Some thermodynamic values relevant for the growth kinetics are estimated by comparison of the calculation with the experiment. It is also shown that the deadsorption-rate constant of Se atoms from ZnSe(100) surface is obtained when the model is applied to explain the result reported by Yao et al., and it is in agreement with the one deduced from our experimental result.

Highly efficient pGaSb‐nGa1−xAlxSb photodiodes

Highly efficient pGaSb‐nGa1−xAlxSb photodiodes were fabricated by liquid‐phase‐epitaxial growth of an undoped p‐type GaSb layer, followed by that of an n‐type Ga1−xAlxSb layer with a composition at x=0.7 on a p‐type (100) GaSb substrate. Spectral photocurrent response of the diodes measured at various bias voltages and room temperature was fairly flat between 1.0 and 1.7 μm. The external quantum efficiency of the photoresponse was 38% at zero bias and 54% at 1 V reverse bias in the vicinity of 1.2 μm.

Composition control of GaAsP grown by molecular beam epitaxy

Abstract This paper describes composition control of GaAsP alloy grown by molecular beam epitaxy. The relationship between the growth condition and the film composition is explained applying a precursor state growth model to GaAsP growth. The activation energies and the parameters appearing in the relationship are determined by fitting the calculated compositions to the experimental ones. The effect of flux intensities, substrate temperature and growth rate on the composition is discussed.

MBE growth mechanism of ZnSe: growth rate and surface coverage

Abstract The growth rate and surface coverage as functions of growth temperature and molecular beam intensity for MBE growth of (100)ZnSe are examined by the model accounting for the precursor states and surface coverage. The calculated results on the growth rate are presented and the growth temperature and flux ratio dependence of growth rate is described. The calculated results on the surface coverage are also presented. It is found that the growth temperature should be chosen at around 360°C in order to achieve surface stoichiometry during MBE growth. The correlation between surface coverage and experimental RHEED patterns is also reported.

A highly stable long‐life GaP‐GaAlP heterojunction cold cathode

By a new activation method, namely, activation by Cs, Sb, and O2, stabilized cold cathodes could be obtained, and continuous operation over 3000 h has been achieved with a GaP‐GaAlP cold cathode. It is found that a major source of rapid efficiency loss of the cold cathode is the loss of Cs and/or O2 from the cold‐cathode surface.

Surface Processes in ALE and MBE Growth of ZnSe: Correlation of RHEED Intensity Variation with Surface Coverage

The surface processes in ALE (atomic layer epitaxy) and MBE (molecular beam epitaxy) are investigated both by numerical calculation for the surface coverage based on the model proposed by the authors and by in situ observation of the RHEED intensity variation. The sublimation process is dominated by the Se sublimation from the surface and the adsorption process is influenced by the desorption of Se from both the surface and the precursor states in the range of practical ALE and MBE growth temperatures. To achieve the layer-by-layer growth during ALE the substrate temperature should be set below 300°C. It is also shown that the RHEED intensity variation corresponds to the change in surface coverage during ALE and MBE growth as determined via comparison of the model calculation for surface coverage with the experimental RHEED data.

Cleaning of gap surface by forming oxide film

Abstract Forming an oxide film on GaP crystal was found effective for removing carbon contaminants from its surface by heating in an ultra high vacuum. AES signal from the carbon on the GaP surface with the oxide film disappeared by heating at 630° C. The clean surface thus obtained showed clear LEED patterns which were composed of the superposition of diffraction from facets of {110} and from a native surface.

Microstructure of Alkoxide-Prepared Lead Zirconate Titanate Actuator

A low-hysteresis lead zirconate titanate (PZT) actuator with fine-grained ceramics is realized by an alkoxide method followed by a hot isostatic press (HIP) or a hot-press method. The HIP or the hot-press method is effective for increasing the density of the fine-grained actuator without further grain growth. It is concluded from the transmission electron microscopy (TEM) observations that the fine-grained ceramics are composed of grains with a size of around 1 µm, which include still smaller particles ranging from 20 nm to 50 nm in size. The smaller particles seem to be traces of the boundaries of the alkoxide-prepared starting powders. The improved hysteresis characteristics may be related to the traces left in the component grains.