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The distribution of dislocations in strontium barium niobate (SBN) crystals is examined by etching and by optical microscopy, and the sources of the dislocations are also investigated. The dislocations can be put into three categories according to the characteristics of distribution patterns. The dislocations concentrated in the central region of the crystal originate from the dislocations and the residual surface damages in the seed. The dislocations aligned radially in the outer region of the crystal are generated by the lattice mismatching or thermal stress at the groove bottoms in the shoulder part of the crystal. Finally, the dislocations distributed randomly in the outer region are generated at the positions where Pt or SBN were adsorbed on the surface of the crystal body. Methods for eliminating the dislocations are also described.

A gadolinium molybdate single crystal β'–Gd2(MoO4)3 grown by the Czochralski technique was observed by using chemical etching and X-ray transmission topography. It was found that there were flat helical dislocations and rows of flat closed loop dislocations having axes parallel to the <110> directions in this crystal. The Burgers vectors were found to be parallel to the axes of these dislocations. Moreover, one to one correspondence between the etch-pits and the images of dislocations in X-ray topographs was observed.

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The influence of active layer thickness and p-type dopants for a cladding layer on laser reliability was investigated using GaAlAs modified channeled substrate planar (MCSP) lasers operating at around 780 nm. The proportion of short-lived lasers increases abruptly when the active layer thickness becomes less than 0.04 µm. This phenomenon is attributed to the abrupt increase of carrier density in the active layer at the lasing threshold. Zinc was found to be superior to germanium as a p-type dopant of the cladding layer in terms both of the temperature dependence of the threshold current, and of laser reliability. A cumulative failure rate as low as 2.7% over 2000 hour operation at 70°C was achieved for MCSP lasers having an active layer thickness and Zn concentration of the cladding layer that were optimized.

Compositional profiles of epitaxial normalGaAlAs layers grown by liquid phase epitaxy using the supersaturation technique were investigated in relation to the growth conditions by laser Raman spectroscopy. In the diffusion limited process with a flat temperature profile during epitaxial growth cycle, a uniform layer of 1.26±0.017 μnormalm false(±1.3%false) with a small compositional variation of 0.457±0.007 false(±1.5%false) can be accomplished. On the other hand, remarkable compositional variations (> ± 10%) occur during an initial growth stage, which depends on the initial supersaturation. Compositional uniformity is improved to 0.152±0.007 false(±4.6%false) by decreasing initial supersaturation to 2.5°C.

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