Tomoki Inada

Observation of edge-facets in 〈100〉 InP crystals grown by LEC method

Abstract The growth of edge-facets on 〈100〉 InP crystals has been investigated using microscopy. The solid/liquid interface in the region of edge-facets was found to have a knife-edged shape, while that of a region without facets had a smooth shape. The irregular patterns of edge-facets point to instability in the growth at the periphery of a crystal, and this instability is found to be related to the generation of twins.

LEC growth of large GaAs single crystals

Abstract As the origin of polycrystallization in LEC grown GaAs crystals, accumulation of dislocations has been studied by microscopic observation of polycrystallized crystals. It has been found that dislocations have a tendency to propagate perpendicular to the solid⌜quid interface during growth. The shape of the interface near periphery of the growing crystal is usually concave towards the melt, this concave interface can lead to an accumulation of dislocations. This allocation causes polycrystallization. By control of the growing interface shape, polycrystalline growth has successfully been suppressed. Using this technology, GaAs single crystals of 75 mm diameter and 500 mm long, of 100 mm diameter and 320 mm long, and of 150 mm diameter and 170 mm long have been obtained with good stability.

Effects of thermal history during LEC growth on behavior of excess arsenic in semi-insulating GaAs

Abstract The effects of the thermal history during the LEC growth of a semi-insulating GaAs crystal are discussed from the viewpoint of changes of the behavior of the excess arsenic dissolved in the GaAs crystal. Near the melting point, solid-solution of excess arsenic is observed in the crystal. In the B2O3 layer, both the formation of EL2 and the generation of scattering centers occur, and the two phenomena are competitive. In the ambient gas, the homogeneous nucleation of arsenic occurs.

Investigation of changes of As precipitates in semi-insulating GaAs crystals at several temperatures by infrared light scattering tomography

Abstract Thermal behavior of arsenic precipitates in undoped semi-insulating GaAs crystals has been investigated. Crystals heat-treated at a temperature between 500 and 1150°C were observed by infrared light scattering tomography, which is powerful technique capable of detecting the arsenic precipitates. The arsenic particles on the dislocations became large increased in scattering intensity with temperatures from 800 to 1000°C. A dramatic change occurred above 1100°C: the images disappeared over the whole area. This disappearance means that the arsenic precipitates dissolves into the GaAs crystal. Using the samples in which the excess arsenic was solid-soluted, the same experiments were repeated. At 800–1000°C, the scattering images of the dislocations again appeared. Below 600°C, new images, consisting of misty zones of scattering, were observed in the dislocation-free areas. This suggests that the excess arsenic condenses like mist over the limit of saturation solubility.

Effect of Water Content of B2O3 Encapsulant on Semi-Insulating LEC GaAs Crystal

Undoped LEC GaAs crystals were grown in PBN crucibles using dry and wet B2O3. The influence of the water content of B2O3 on the melt composition and the electrical properties of the crystal was examined, and it was found that when a highly Ga-rich charge composition was used, crystals grown using wet B2O3 became semi-insulating, while crystals grown using dry B2O3 were p-type conductive. The purity of crystals was investigated through SIMS analysis, LVM IR absorption measurement, and 3He activation analysis.

Growth and properties of InP single crystals grown by the magnetic field applied LEC method

Abstract The effect of a magnetic field on the properties of InP melt and grown crystals have been investigated. Temperature fluctuations in the melt were effectively reduced to less than 0.3°C at 1000 G. Neither irregular growth striations nor microscopic defects, such as “grappes” or dislocation clusters, were observed in the 50 mm diameter crystals grown under a magnetic field of 1000 G. A low etch pit density of 6 x 10 3 cm -2 was obtained on average for undoped crystals, and dislocation-free S-doped crystals co-doped with Ga and Sb were obtained under the magnetic field.

Study of nonstoichiometry in undoped semi-insulating GaAs using precise lattice parameter measurements

Nonstoichiometry in undoped semi‐insulating GaAs grown by the liquid‐encapsulated Czochralski technique has been evaluated by absolute lattice parameter measurements using the Bond method. The lattice parameter increases with increasing As atom fraction in the initial melt. The observed range of lattice parameters and the variation along the growth direction suggest that the solidus curve in the phase diagram extends to the As‐rich side than to the Ga‐rich side, and the congruent point is located on the stoichiometric point or the slightly As‐rich side.

Growth of semi‐insulating GaAs crystals with low carbon concentration using pyrolytic boron nitride coated graphite

It has been determined that the incorporation of carbon into GaAs crystals grown by the liquid encapsulated Czochralski method occurs as the result of a reaction between the GaAs melt and gaseous oxides of carbon, rather than carbon particles. The incorporation occurs during growth as well as during synthesis. The incorporation of carbon was particularly large when a commercially available large puller was used because of the greater number of carbon components in the hot zone which act as sources. Crystals with a low carbon concentration of 1×1015 cm−3 have been successfully grown by employing pyrolytic boron nitride coated graphite components in the large puller.

Inhomogeneity of Resistivity in In-Doped Dislocation-Free Semi-Insulating LEC GaAs

In-doped dislocation-free semi-insulating GaAs crystals were prepared from various melt compositions and measurement of resistivity distributions and infrared absorption at 1 ?m were carried out. Inhomogeneity of resistivity, both along the radial and longitudinal directions, was observed even in some dislocation-free crystals. This inhomogeneity strongly depends on melt composition, and is mainly due to non-uniform distribution of stoichiometry-related defects revealed by infrared absorption measurement.

Quasi-quantitative estimation of solidus curve on As-rich side of Ga-As system

Abstract A quantitative investigation of the solidus curve on the As-rich side of the Ga-As system was done by estimating the amount of excess As in crystals grown from As-rich melts. Excess As atoms in a GaAs crystal are usually subjected to two forms: precipitation and dissolution. To obtain the solidus curve, it was assumed that the EL2 concentration gives the composition of the crystal when almost all the dissolved excess As form EL2. The maximum EL2 concentration was produced in crystals by a new thermal treatment that dissolves As precipitates and is assumed to change almost all the dissolved As into EL2. The maximum EL2 concentration showed a strong linear correlation with the melt composition. A solidus curve has been drawn that has a parabolic shape similar to the liquids curve. The congruent point is shifted from stoichiometry toward the As-rich side by an amount equivalent to an EL2 concentration of 10 16 cm -3 .