Kazuhiro Kurata

The pseudo-binary V2VI3-IV·VI compounds systems, Bi2Te3-PbTe, Bi2Te3-SnTe, Sb2Te3-PbTe, Sb2Te3-SnTe and Bi2Se3-SnSe

Abstract Phase diagrams of pseudo-binary systems of some V 2 VI 3 -IV·VI compounds have been investigated by thermal analysis and X-ray diffraction. The proposed phase diagrams of the Bi 2 Te 3 -PbTe and Bi 2 Te 3 -SnTe systems show single peritectic intermediate compounds and eutectic reactions between Bi 2 Te 3 and these compounds. The phase diagrams of Sb 2 Te 3 -PbTe and Sb 2 Te 3 -SnTe are of the eutectic type. A continuous series of liquidus points over the entire concentration range typifies the Bi 2 Se 3 -SnSe system.

Derivation of new semiconducting compounds by cross substitution for group IV semiconductors, and their semiconducting and thermal properties

Abstract The derivation of new semiconducting compounds by cross substitution of group IV semiconductors was studied. The quaternary compounds, Cu2HgGeSe4, Cu2HgGeTe4, Cu2HgSnSe4, CuCd2GaSe4, CuCd2InSe4, CuCd2InTe4, AgCd2InSe4, Cu5InGe2Se8, Cu3InGeSe5, were found from the survey of 17 combinations of groups of elements. The phase diagrams between HgSeCu2GeSe3, HgTeCu2GeTe3, HgSeCu2SnSe3, related to Cu2HgGeSe4, Cu2HgGeTe4, Cu2HgSnSe4 respectively, Cu2HgSnSe4Cu2HgGeSe4, and Cu2HgGeTe4Cu2HgGeSe4 were determined by thermal analysis. Semiconducting and thermal properties of 8 new compounds and related alloys of 4 solid solution systems were determined. The thermoelectric figure of merit is of the order of 10−4 °C−1 for these materials.

An experimental study on improvement of performance for hemispherically shaped high-power IRED's with Ga 1-x Al x As grown junctions

This paper describes the structure and performance of a high-power infrared emitting diode (IRED) designed as a high speed optical beam source for optoelectronic applications. The heterostructured junction is formed on a thick Ga1-xAlxAs liquid phase epitaxy (LPE) grown layer which is used to shape hemispherical emitting surfaces. Dislocation density in recombination region was considerably decreased by the thick layer growth on a GaAs wafer used as a primary substrate. Under dc operations, external quantum efficiencies of around 45 percent at a current density of 0.6 kA/cm2and about 110 mW of optical output power at 200 mA (1 kA/cm2) have been obtained from the diodes with a 160-µm junction diameter. The tendency to reach power saturation with increased current has been decreased by means of reducing of thermal resistance of the mount, and the diodes with 240- µm junction diameter have shown about 180 mW at 600 mA dc and 1.4 W at a 4-A pulse (60 Hz, 50 µs). A large improvement in high frequency response has been obtained and the bandwidth at -3-dB intensity has reached above 120 MHz.

Lattice mismatch at the interface in GaP-GaP and GaAIAs-GaAs epitaxial growth

Abstract The lattice mismatch at the epitaxial layer-substrate interface was studied by X-ray diffraction techniques for both GaP/GaP and GaAlAs/GaAs epitaxial growth from the liquid phase. A planar defect at the interface, whose fault vector is normal to the interface, was observed. This defect is due to a lattice mismatch between the epitaxial layer and the substrate, however the deformation of the unit cell in the epitaxial layer is such that the lattice expands or contracts normal to the substrate but the lattice spacing parallel to the substrate does not change. The volumes of the unit cells in the epitaxial and the substrate crystal are different due to the difference of nitrogen concentration (GaP/GaP) or heteroepitaxy (GaAlAs/GaAs). The origin of this lattice mismatch was also related to the growth conditions. It was found that the lattice mismatch occurred depending on the magnitude of the gradient of the lattice parameter in the epitaxial layer.

Near-infrared high-power LED's with Ga 1-x Al x As epitaxially grown junctions

This paper reports on a study of several techniques of fabricating an efficient Ga 1-x Al x As IRED with high power. Smooth epitaxial layers are grown on a substrate containing a thick Ga 1-x Al x As epitaxial layer which is used to form a hemispherical emitting surface. This is achieved by using a melting-back technique without up-heating. An effect of the AlAs molefraction ratio between n- and p-type regions was clearly found by measurement of a large number of diode chips, and the best performances were obtained on the junctions with the ratio X_{n}/X_{p} \simeq 1.5 . Ohmic contacts to the p and n regions were applied on the same surface of the wafer using only one metallic source for the vacuum deposition. A cerium-oxide film serves as an antireflection coating when deposited on the hemispherical surface and increases the optical output power by more than 30 percent. External quantum efficiencies of 28 percent (current density: 400 A/ cm2) and optical output power of 96 mW (drive current: 300 mA, current density: 1500 A/cm2) have been observed from diodes emitting at 8300 A under dc operation at room temperature.

Effect of Donor Concentration on Several Properties of Gallium Arsenide Phosphide

The effects of donor concentration on electrical and electroluminescent properties in vapor-grown GaAs0.62P0.38 single crystals are investigated at 300 K. Electron mobility decreases rapidly for ND(donor concentration)> ~1017cm-3, and the obtained maximum electron mobility is 3150 cm2/V.s (ND=1.54×1015cm-3). It is revealed that heavily doped (ND≈1017cm-3) samples show a relatively strong infrared emission spectrum peaked at ~9500A and that this infrared emission causes different behaviors in I–ηext (the quantum efficiency) curves between the samples of low and high donor level.

High-power and high-speed characteristics of modified heterostructure IRED's

A modified heterostucture Ga1-xAlxAs near infrared emitting diode is described with single (SH) and double heterostructures (DH) adopted for carrier confinement. The active region is arranged in a layer for best crystal quality as shown by photoluminescence measurement. The maximum 3-dB bandwidth is 175 MHz and optical output power reaches 7 mW in a surface emitting diode. The experimental results are compared with optical characteristics for SH and DH IREDs.

Phase diagrams of the pseudo-binary Cu2SeBi2Se3 and Ag2SeBi2Se3 systems and thermoelectric properties of Cu2SeBi2Se3 solid solution

Abstract The phase diagrams of the pseudo-binary systems Cu 2 SeBi 2 Se 3 and Ag 2 SeBi 2 Se 3 were determined by thermal analysis. The Cu 2 SeBi 2 Se 3 system has complete solid solution over all compositions, and a minimum melting point at about 33 mol. % Bi 2 Se 3 . The phase diagram of the Ag 2 SeBi 2 Se 3 system is composed of two eutectic phases and one congruently melting intermediate compound at the middle of the system. Thermoelectric figure of merit of Cu 2 SeBi 2 Se 3 solid solution was determined as a function of composition, and maximum thermoelectric figure of merit in this system is expected as z max = 0·43 × 10 −3 deg −1 at 90 mol. % Bi 2 Se 3 .