Masaru Kawachi

Superiority of group VII elements over group III elements as donor dopants in MOCVD ZnSe

Abstract Comparison of group III and group VII elements as donor species in ZnSe MOCVD growth has been studied from the viewpoint of their electrical properties, luminescence qualities and their controllabilities. Low resistivity high quality blue emitting ZnSe has been grown by doping a group VII donor chlorine, in atmospheric MOCVD. The superiority of group VII elements over group III elements with regard to carrier concentration controllability and carrier producing efficiency has been predicted.

Growth of ZnSe crystals by nonstoichiometric annealing

Abstract The grain growth of polycrystalline ZnSe by nonstoichiometric annealing has been studied. It has been found that grains grew from 10 μm to 10 mm in diameter by annealing in selenium atmosphere for two weeks at 1000°C, while samples annealed under a zinc ambient grew up to 2 mm. The color of the crystals changed markedly; the selenium annealed sample became pure green, whereas those annealed under a zinc ambient remained yellow. The residual impurity concentrations in the annealed samples have been found to be less than those in boules obtained by other techniques.

Transparency Improvement of Potassium Titanyl Phosphate (KTP) Crystals by Annealing under Oxygen Atmosphere

We have studied the influence of iron impurity, and the effects of annealing on KTiOPO4 single crystals. It was found that in high-power second harmonic generation, the iron concentration should be minimized. Annealing at 800°C caused the optical absorption edge to shift 5-10 nm towards shorter wavelengths, and for undoped crystals, the optical transmittance was also increased. Annealing in atmospheres of increasing oxygen concentration increased the transparency. A high recovery capability against X-ray irradiation damage was also obtained after annealing. The measured full width at half-maximum of the X-ray diffraction (800) peak was apparently decreased in annealed crystals.

Characteristics of ZnSe crystals annealed under host atom atmospheres

Abstract The characteristics of ZnSe crystals grown by nonstoichiometric annealing have been studied. Their optical characteristics, the driving force for the anomalous grain growth of polycrystalline ZnSe, and impurity interaction are discussed in terms of optical absorption, X-ray measurements, impurity analyses and TEM measurements. The results of PL measurements suggest that the band gap energy of ZnSe crystals grown under a selenium atmosphere became about 28 meV smaller than that of other crystals grown by other techniques. The dominant driving force for grain growth is the surface energy of polycrystalline ZnSe. A cluster of atoms in a crystal grown under a selenium atmosphere has a tendency to move easily during TEM observation with a focused electron beam. This tendency causes the anomalous grain growth under a selenium atmosphere. The intentionally added impurity, iodine, has been found to suppress the grain growth. The residual impurities were highly concentrated at the grain boundaries.

Grating axicon for collimating Cerenkov radiation waves.

An axicon optical element that utilizes a diffraction grating has been fabricated for collimating the Cerenkov radiation wave. The grating axicon has the advantage of a simple structure, which can easily be fabricated by the computerized numerical control machining technique. The collimation function of the grating axicon is confirmed for Cerenkov-type second-harmonic generation in LiNbO(3) waveguides, and correction of the aberration caused by substrate anisotropy is investigated. The aberration can be compensated by appropriately inclining either the substrate facet or the grating axicon.