Iwao Teramoto

Etch Pits and Polarity in CdTe Crystals

Two types of etch pits in cadmium telluride have been observed. The etchants used are nitric acid solutions of potassium bichromate which also contain silver ions of various concentrations. The etch pits resulting from etch (EAg‐1) grow into a tetrahedral shape bounded by the crystallographic habit planes and reveal geometrical polarity on the (111) and (111) surfaces. Another type of etch pit is formed at a different point from that of the pit with EAg‐1 by the modified etch (EAg‐2), which has increased content of Ag+ ion. The two types of etch pits, with EAg‐1 and with EAg‐2, are believed to be associated with Cd and Te edge dislocations. The dissolution rate and its selectivity to the constituent elements in cadmium telluride is controlled electrochemically by the variation of the Ag+ ion concentration of the etching solution. The structure of the twin boundary is also studied by etching and back Laue techniques.

New heteroisolation stripe-geometry visible-light-emitting lasers

Visible-light-emitting lasers were fabricated, using a new stripe-geometry double heterostructure. The distinct feature of the geometry is the isolation of the contact stripe electrode to p-GaAs by the use of a layer of n-Ga 1-z Al z As epitaxially grown on top of p-GaAs. This geometry results in small internal strain, few crystal imperfections, and low thermal resistance in diodes so that high laser performance can be obtained. Lasing wavelengths as short as 7610 A and 6680 A have been attained in CW and pulsed operation, respectively, at room temperature. Various characteristic features of the lasers are described with regard to optical spectra, lasing thresholds, and external quantum efficiencies.

Relations between the electronic properties and the chemical bonding of sbxBi2−xTe3−ySey system

Abstract The electronic properties of SbxBi2−xTe3−ySey were investigated. The materials were prepared by melting, quenching and annealing. It is found that y0, the value of y for which the thermoelectric power reverses from p-type to n-type, coincides with the electrical conductivity minimum, and increases with increasing x. An explanation of the results is proposed based on a model of chemical bonding in compounds of the type Av2BVI3. The smaller value of y0 for x = 0 than for x = 1.0 is interpreted by taking into account the additional effect of the variation of carrier mobility with y. X-ray analysis shows that the system is a continuous solid solution with the hexagonal structure except for the region whose composition is close to Sb2Se3. Curves of the electrical conductivity and the thermoelectric power are discontinuous, where the admixture phases of hexagonal and orthorhombic structures are shown.

Cd and Te Dislocations in CdTe

It seems probable that two types of 60° edge dislocation exist in CdTe because of the geometrical polarity. In fact, such types of dislocations can be made visible as different etch pit figures with two kinds of etches. Two types of bendings were applied for the introduction of either excess‐Cd or excess‐Te dislocations. On each bending two types of dislocations were simultaneously brought about with a minimum in density near the neutral plane. However, annealing at high temperature resulted in a uniform distribution of dislocations and a polygonization of the crystal. Furthermore, it was found that dislocations of the correct sign, necessary to produce the required configuration of bending, were predominantly conserved while unexpected dislocations were thermally annihilated during the polygonization process.

Improvement in operation lives of GaAlAs visible lasers by introducing GaAlAs buffer layers

It is shown that drastic reduction of the active-layer stress can be obtained by the introduction of a GaAlAs buffer layer in GaAlAs visible lasers. The life tests of the GaAlAs visible lasers with the optimally designed buffer layers were carried out at 50°C in a dry nitrogen ambient. The results indicate that the introduction of the optimal buffer layer leads to a reduction in the stress induced degradation of GaAlAs visible lasers.

Very low threshold visible TS lasers

Fundamental transverse mode lasers with very low threshold currents have been realized by use of the modified terraced substrate (TS) geometry. The threshold currents of 250 μm cavity length lasers at room temperature are typically 20-30 mA for wavelengths around 750 nm. In the 710 nm laser, which is the shortest lasing wavelength in this work, the threshold is as low as 70 mA in CW operation. The 726 nm laser was operated for only 150 h, while a lifetime longer than 10 000 h is expected for TS lasers with a lasing wavelength longer than 750 nm.

Fundamental transverse and longitudinal mode oscillation in terraced substrate GaAs-(GaAl)As lasers

A new, simple structure for a stripe-geometry laser is proposed. A double heterostructure is fabricated on a terraced substrate, providing a modified rib-waveguide structure in the active layer. A lasing mode is confined and stabilized in the narrow area between two adjacent bends of the active layer. The terraced substrate laser exhibits a stable, single longitudinal mode oscillation as well as a fundamental transverse mode oscillation in CW operation. No kinks have been observed in light-output versus current characteristics. The linearity continues up to ten times the threshold in the pulsed operation at which the power output is 150 mW per facet.

The stress‐enhanced diffusion of boron in silicon

The stress effect on diffusion of impurities in the fabrication of silicon avalanche photodiodes was found when thick diffusion masks of SiO2 were used. The observation of the avalanche multiplication profile showed that nonuniform diffusion occurs over the window area of the mask. From the qualitative analysis, it is concluded that the diffusion coefficient is represented by the sum of the zero‐stress term and the stress‐induced term.

Behavior of Gold in Cadmium Telluride Crystals

The kinetic behavior of gold atoms in cadmium telluride single crystals has been studied at temperatures above and below 600°C. The diffusion coefficient was determined over the temperature range of 600°∼1000°C using autoradiographic technique by diffusing radioactive gold into cadmium telluride. The relationship between temperature and volume diffusion coefficient is found to be D =67exp (-2.0 eV/ k T ) cm 2 /sec. At temperatures below 400°C, the hole concentration in gold-doped crystals is observed to decrease by heat treatment, according to an equation N = N 0 exp (- t /τ), where τ is a time constant dependent on temperature and dislocation density. It is shown that the experimental results are interpreted by the terms of the segregation of gold atoms to α and/or β 60° edge dislocations.

Embedded-stripe GaAs-GaAlAs double-heterostructure lasers with polycrystalline GaAsP layers - I: Lasers with cleaved mirrors

We report a new type of embedded stripe laser in which low-order mode CW oscillation is successfully attained at room temperature. In order to achieve lateral current confinement, a high-resistivity polycrystalline GaAsP layer is formed around the mesa stripe by selective vapor-phase growth technology. It turns out that a stable single-mode operation is attained at an injected current up to several times the threshold value.