K. Balakrishnan

Drop experiments on crystallization of InGaSb semiconductor

Abstract Drop experiments have been performed to study the crystallization of InGaSb under different gravity conditions. Formation of spherical projections on the surface of InGaSb during its crystallization was in situ observed using a high-speed CCD camera. Spherical projections showed dependence on gravity during its growth. The projections formed under microgravity were almost spherical, whereas the projection formed under normal gravity was not perfectly spherical. Indium compositions in the spherical projections were found to vary with temperature.

Numerical analysis of the dissolution process of GaSb into InSb melt under different gravity conditions

Abstract In order to support the process of growth of high-quality InGaSb single crystals, a numerical simulation has been carried out to clarify effects of temperature gradient, heating rate, and gravity level during the dissolution process. A sandwich model of GaSb/InSb/GaSb combination has been used, where GaSb is in solid state and InSb is in molten state at the start of calculation. The amount of GaSb dissolved into the InSb melt decreased and the solid–liquid interface changed from asymmetric to symmetric shape with increase of temperature gradient. The dissolved amount decreased with increased heating rate without holding of temperature. However, holding process increased dissolution. The combination of high heating rate and holding of temperature was more suitable than stable heating with a low heating rate to achieve steady state in a shorter time. The shape of the solid–liquid interface was strongly distorted under 1xa0G condition, but it became flat and iso-concentration lines became parallel to the interface as the gravity level was reduced.

Numerical simulation of effect of ampoule rotation for the growth of InGaSb by rotational Bridgman method

Abstract To investigate the solution convection for the rotational Bridgman method, both flow patterns and temperature distributions in the In–Ga–Sb solution were calculated. In the three-dimensional model, In–Ga–Sb solution was put between a GaSb seed and feed crystals, where the seed and feed crystals were of cylindrical shape, and the In–Ga–Sb solution was of semi-cylindrical shape. The flow velocity in the In–Ga–Sb solution increased and the temperature distribution tended to be uniform with increase of the ampoule rotation rate. When the ampoule rotation rate was 0xa0rpm, the temperature difference at the solid–liquid interface increased with an increase of the aspect ratio. However, with an increase of ampoule rotation rate, the temperature difference became small. The stirring effect of the ampoule rotation was enhanced with an increase of rotation rate as the forced convection became dominant in the In–Ga–Sb solution.

Growth of InxGa1−xAs bulk mixed crystals with a uniform composition by the rotational Bridgman method

To grow In x Ga 1-x As (x = 0.03-0.15) ternary bulk crystals with uniform composition and high quality, we have modified the rotational Bridgman method to feed GaAs sources continuously into In-Ga-As solution. In the case of In x Ga 1-x As grown directly on a GaAs seed, it was possible to grow In x Ga 1-x As single crystals with an In composition up to 0.1 (x). The maximum thickness of the In x Ga 1 As single crystals was 6.5 mm. The In compositional ratios in these crystals were homogeneous due to the feeding of GaAs sources continuously into the In-Ga-As solution. With the increase of the In compositional ratio, the X-ray diffraction FWHM increased and the grown crystal/seed interface became rough. In the case of multi-step growth, the FWHM decreased to one quarter of the value of that grown directly on the GaAs seed. The interfaces at each step were flat and smooth. Furthermore, it was found that the influence of lattice mismatch decreased when using the multi-step growth method.

Microravity experiments on melting and crystallization of InGaSb

Abstract Drop experiments have been performed to study the crystallization of In0.05Ga0.95Sb and the melting behaviors of InSb and GaSb under different gravity conditions. Formation of spherical projections on the surface of InGaSb during its crystallization was in-situ observed using a high speed CCD camera. Spherical projections showed dependence of gravity during its growth. Indium compositions in the spherical projections were found to vary depending on the temperature. Melting velocities of InSb and GaSb crystals under the microgravity condition were found to be faster than those under normal gravity condition (1G).

Optimization of circular trench geometry of GaAs(1 1 1)B substrates for growth of high quality InxGa1-xAs bridge layers

Abstract An attempt has been made to further improve the quality of In x Ga 1− x As ( x =0.06) bridge layers on GaAs (1xa01xa01)B trench substrates by depositing SiN x on the inner surfaces of the trenches. In x Ga 1− x As ( x =0.06) layers grown in this way were found to exhibit better quality, as evidenced by microscopic photoluminsecence measurements. The trapezoidal SiN x film of large area deposited over the inner surface of the trench was found to be effective in reducing the dislocation content of the bridge layer. The minimum and maximum diameters of the trenches on GaAs(1xa01xa01)B substrates, keeping other parameters constant, under which the growth of In x Ga 1− x As bridge layers is possible have been determined.

A novel method to grow high quality In1−xGaxAs ELO and bridge layers with high indium compositions

Abstract High quality In 1− x Ga x As ( x =0.2) layers were grown on composition-converted InAs(1xa01xa01) patterned substrates by liquid phase epitaxy. Epitaxial lateral overgrown In 1− x Ga x As ( x =0.2) layer with flat and mirror-like surface was obtained on trenchless substrates. Clean bridge layer of In 1− x Ga x As ( x =0.2) was not formed when the trench substrate was used. When the trench substrate with SiN x deposition at the trench bottom was used, In 1− x Ga x As ( x =0.2) bridge layer resulted. The etch pit density of the bridge layer was found to be low. Ga and In contents of the In 1− x Ga x As ( x =0.2) epitaxial layers grown on all types of composition-converted InAs substrates were found to be uniform.

The coalescence of ELO layers of InxGa1-xAs grown on patterned (111) GaAs by liquid phase epitaxy

InxGa1-xAs (x = 0.06) epitaxial lateral overgrown (ELO) layers were grown on (111)B GaAs patterned substrates covered with SiNx masks by liquid phase epitaxy. The thickness of the ELO layer with a { 111} A growth front was found to decrease as the growth progressed. On the other hand, for the ELO layer with a { 111} B growth front, this kind of decrease of thickness was found to be very small. When the layers with different growth fronts ({ 111} A and { 111} B) coalesced, dislocations were found to be generated. In the case of the coalesced ELO layers which were in constant contact with the basal SiNx mask, the surface became concave due to the decrease of thickness of the layers. This problem of decrease of thickness was not observed when a large enough void structure was present in the grown ELO layers of InGaAs.

Growth of InxGa1−xAs layers with pyramidal morphology on (100)GaAs patterned substrates by liquid-phase epitaxy

Abstract Liquid-phase epitaxial growth of In x Ga 1− x As ( x =0.6) layers on various types of patterned (1xa00xa00)GaAs substrates was investigated. Non-planar InGaAs layer having filled tent-like structure was grown on non-patterned substrate. When the InGaAs was grown on circular-patterned substrate, a non-hollow pyramid structure was obtained. Perfect hollow pyramid structured InGaAs was found to be grown on trench substrates of (1xa00xa00)GaAs.