Masashi Kumagawa

Epitaxial Growth with Light Irradiation

The effects of light irradiation on crystal growth were investigated in the vapor epitaxial growth of silicon. It was observed that the activation energy of crystal growth decreased with light irradiation. The magnitude of the decrease was 2.1 kcal/mole under the typical experimental condition in an rf heating reactor. Crystal growth was carried out at a temperature lower than that used in the conventional epitaxial method, and the crystal quality of the grown layers was found to be better in the case with light irradiation than that without irradiation. The above results suggest that light irradiation techniques can be used for reducing the degradation of impurity distribution by decreasing the growth temperature. At present, selective crystal growth according to an irradiation pattern can be realized. It is expected that epitaxial growth with light irradiation can be applied to a selective growth process.

Experimental and numerical investigations on dissolution and recrystallization processes of GaSb/InSb/GaSb under microgravity and terrestrial conditions

The effects of gravity and crystal orientation on the dissolution of GaSb into InSb melt and the recrystallization of InGaSb were investigated under microgravity condition using a Chinese recoverable satellite and under normal gravity condition on earth. To investigate the effect of gravity on the solid/liquid interface and compositional profiles. a numerical simulation was carried out. The InSb crystal melted at 525 degrees C and then a part of GaSb dissolved into the InSb melt during heating to 706 degrees C and this process led to the formation of InGaSb solution. InGaSb solidified during the cooling process. The experimental and calculation results clearly show that the shape of the solid/liquid interface and compositional profiles in the solution were significantly affected by gravity. Under microgravity, as the Ga compositional profiles were uniform in the radial direction. the interfaces were almost parallel. On the contrary, for normal gravity condition, as large amounts of Ga moved up in the upper region due to buoyancy, the dissolved zone broadened towards gravitational direction. Also. during the cooling process, needle crystals of InGaSb started appearing and the value of x of InxGa1-xSb crystals increased with the decrease of temperature. The GaSb with the (111)B plane dissolved into the InSb melt much more than that of the (111)A plane

Effect of Ultrasonic Vibrations on InSb Pulled Crystals

InSb single crystals were pulled from the melt by the Czochralski method. During the growth of the crystals, ultrasonic vibrations were introduced into the melt through the carbon crucible. The facet region at the center of the pulled crystals shifted to the periphery of the crystals and simultaneously decreased in size, because the ultrasonic vibrations stirred the melt and raised its temperature. Furthermore, the difference in the values of the spreading resistance between the facet and the off-facet regions also decreased. These results indicate that inhomogeneous distributions of impurity concentration in the crystals were improved by the introduction of ultrasonic vibrations.

Hydrogen Etching of Silicon Carbide

The etch rate of SiC crystals with hydrogen was investigated as a function of the reaction temperature, the hydrogen flow velocity and the hydrogen partial pressure in the H2-Ar mixture. An etching reaction mechanism and calculated expressions for the etch rate have been developed based on thermodynamical considerations. The experimental results are well explained from the approximate expression at the etch rate region higher than about 3 µ/min.

The effect of the substitution of Sm for Ba on the superconductor

Characteristic changes occurring in superconductors on substituting Sm for Ba have been investigated. An appropriate amount of Sm substitution (, in the form of ) promoted grain growth; the grain size became larger than that in the non-substituted sample and had a maximum value at x = 0.07. Single-phase samples were obtained for . The critical temperature increased by about 1.5 K for concentrations up to x = 0.02, while it decreased rapidly beyond this amount. Samples did not show superconductivity above 15 K for . The crystal structure transformed from orthorhombic to tetragonal at x = 0.3. The average valency of the Cu and the oxygen content decreased linearly with increase of x in the ranges of and , while they both increased linearly for the range .

Room Temperature InAsxP1-x-ySby/InAs Photodetectors with High Quantum Efficiency

Room temperature surface-illuminated InAsxP1-x-ySby/InAs photodiodes with an external quantum efficiency as high as 50–86% in a 1.83–3.53 µm wavelength range have been fabricated for the first time. Lattice matched heterostructures with a wide energy gap InAsPSb cap layer were grown on the InAs substrate using the liquid phase epitaxy technique. According to temperature dependence measurements for a 1 mm diameter photodiode, peak responsivities of 1.83–2.5 A/W have been realized in a temperature range of 296 to 200 K. The Johnson noise limited room temperature detectivities D* are deduced to be 1\endash6 ×109 cm·Hz1/2/W at zero bias. It is demonstrated that the only loss of external quantum efficiency is from the reflection of the entrance face.

Growth of III–V ternary and quaternary mixed crystals by the rotationary Bridgman method

The rotationary Bridgman method with high speed rotation of the growth ampoule was used to grow III–V ternary and quaternary mixed crystals. InSb1 − x Bix single crystals grew a maximum of 17 mm thick, but the Bi content increased gradually with growth. So, by feeding source materials, homogeneous InSb1 − x Bix crystals with x = 0.008 were obtained. These crystals were 15 mm thick with a diameter of 14 mm. Further, a Ga1 − xInxAsySb1 − x single crystal layer (x = 0.22−0.24, y = 0.12−0.10) of 1 mm maximum thickness grew on a GaSb seed by floating a lump of GaAs in the Ga-In-Sb solution.

Sulphur passivation of InAs(Sb)

Abstract The sulphur passivation for the InAs surface was studied by photoluminescence (PL) and spectroscopic ellipsometry (SE). Effects of the treatment are compared with I - V characteristics and photoresponse (PR) of MESA structure devices fabricated with LPE multilayer of InAs 1− y (Sb y ). It is expected that the dangling bonds at the surface are terminated in the forms of SIn, SSb bonds by the passivation, which results in a remarkable decrease of surface recombination center density. This phenomenon was confirmed by observing increases of PL intensity and of the PR of photodiodes. Four order reductions of dark current and remarkable increase of PR have been observed on sulphur passivated photodetectors. Stability of the effect of the sulphur passivation was also examined by SE as well as PR measurements. SE measurements showed that dielectric function of the surface layer for the InAs wafer has no absorption in the measured spectral range between 1.5 and 5.5 eV. After sulphur passivation, optical absorption appeared due to submonolayer sulphur atoms in good agreement with the results obtained from the InAs(Sb) photodetectors.

Epitaxial lateral overgrowth of InGaAs on patterned GaAs substrates by liquid phase epitaxy

Abstract In x Ga 1 − x As ( x = 0.06) layers were grown on patterned (1¯1¯1¯) GaAs substrates by liquid phase epitaxy. Two kinds of substrate structures were fabricated by using a GaAs wafer covered with aSiN x film. The first type was a substrate which had only regular windows of 1 mm in diameter in theSiN x film, and the second had trenches of 40–50 μm in depth in theSiN x windows. For trenchless substrates, InGaAs laterally extended on theSiN x film, finally resulted in a hexagonal shape. The etch pit density reduced dramatically on the epitaxial lateral overgrowth layer, but was extremely high on the substrate. For trench-type substrates, InGaAs layers grew laterally from the side wall of a trench towards the inside, forming a star-like pattern composed of {111}A and {111}B planes. Then, this pattern changed to a triangular shape surrounded by {111}B planes since the growth rate of {111}B planes was slower than that of {111}A planes. The InGaAs layer formed a bridge over the trench. As a result, the EPD was extremely low in both layers inside and outside except in the trench periphery. It was shown that the growth of high quality crystals was possible by using a trench-type substrate.

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.