Yasutoshi Kashiwada

The congruent melting composition of strontium barium niobate

The congruent melting composition of strontium barium niobate has been investigated over the ternary composition region by DTA, X-ray fluorescence, Curie temperature and lattice parameter measurements. The composition of congruent melt was found to be close tox=0.61,y=0.4993 for the formula (Srx Ba1−xO)1−y. (Nb2O5)y. Striation-free single crystals are grown from the melt with this composition. The conceivable reasons for the discrepancy between the results of this work and the previous data are briefly discussed.

Highly Reliable GaAlAs Visible-Light-Emitting MCSP Lasers

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.

Dislocations in Strontium Barium Niobate

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.

Thickness control of Ga1−xAlxAs layers grown by liquid phase epitaxy at low growth temperature

The uniformity of a Ga1−xAlxAs layer grown by liquid phase epitaxy was investigated as a function of the growth temperature in the range of 600 to 800°C. Lowering the growth temperature causes the growth rate to decrease, which contributes to remarkable reductions in both the normalized edge growth height (H) and the thickness variation (σ) over the wafer. At a growth temperature of 600°C, the flat Ga1−xAlxAs (solid composition, x = 0.45 ± 0.008) layer of 2.058 ± 0.07 μm (σ/d = 3.4%) can be obtained with an edge growth height of 2.92 μm (H = 1.25). On the other hand, at a short growth time of 0.3 s, the variation of layer thickness of less than ±0.007 μm (±8.9%) does not depend on the growth temperature. The probable lowest limit in a flat layer can be varied by the initial supersaturation.