Yoshihiro Ueta

Band Gap Energy and Band Lineup of III-V Alloy Semiconductors Incorporating Nitrogen and Boron

The band gap energy and band lineup of 15 binary, 42 ternary and 39 quaternary III-V alloy semiconductors composed of (B, Al, Ga, In)(N, P, As, Sb) are calculated by mean of the dielectric method of Van Vechten and the Harrison model, respectively. The alloys including N are predicted to have negative band gap energy in most of the compositional range due to the large electro-negativity of nitrogen atom. Possible material combinations for a lattice-matched doubleheterostructure for blue-light-emitting devices are discussed. The chart presented here will be useful in designing blue-to-ultraviolet light emitters with and without strain in the devices

Blue Laser Diodes Fabricated on m-Plane GaN Substrates

Blue laser diodes (LDs) were fabricated on m-plane oriented GaN substrates by atmospheric-pressure metalorganic chemical vapor deposition. Typical threshold current for stimulated emission at a wavelength λ of 463 nm was 69 mA. Blueshift of the spontaneous emission peak with increasing injection current was examined in LDs fabricated on m- and c-plane GaN substrates. Blueshifts for the m-plane LD (λ=463 nm) and the c-plane LD (λ=454 nm) with an injection current density just below threshold were about 10 and 26 nm, respectively. These results confirm that the blueshift in quantum-wells fabricated on m-plane oriented substrates is smaller than on c-plane oriented substrates due to the absence of polarization-induced electric fields.

Effect of Slight Misorientation of Sapphire Substrate on Metalorganic Chemical Vapor Deposition Growth of GaN

The effects of slight misorientation from c-plane (0001) sapphire (α-Al2O3) substrates on GaN surface morphologies and electroluminescence (EL) properties were studied. The GaN layers were grown using a two-step growth method under atmospheric pressure by metalorganic chemical vapor deposition (MOCVD). When using around 0.17° misoriented sapphire substrate tilted toward both and directions, a small step-type morphology appeared. On the other hand, using c-plain substrate or substrates with the misorientation angle larger than approximately 0.25° from the c-plane, a scale-shaped morphology appears. We also found that the misorientation of the substrate significantly affects the uniformity of the EL image. On the other hand, the light output powers of the light-emitting diodes (LEDs) fabricated on the substrates with different misorientations were almost the same in spite of the different surface morphologies.

AlGaInN Violet Laser Diodes Grown on GaN Substrates with Low Aspect Ratio

AlGaInN violet laser diodes grown on GaN substrates have been studied. Waveguide simulations have been performed and perpendicular radiation angles have been investigated. A peculiar layer structure has been proposed to reduce the perpendicular radiation angle and compared with a conventional laser. The laser structure has an n-cladding layer consisting of three AlGaN films, the middle film of which has relatively high Al composition. A laser diode with an optimized structure has been fabricated. The threshold current density and slope efficiency have been 2.9 kA/cm2 and 1.4 W/A, respectively. The perpendicular radiation angle has been as small as 16.2°. The AlGaInN violet laser diode with a low aspect ratio of 1.6 and a small threshold current of 29 mA has been realized.

X-ray photoelectron spectroscopy study of GaN and GaP surfaces annealed in PH3 and NH3 and metalorganic chemical vapor deposition growth of GaN / GaP heterostructures

Abstract The annealing effects of GaN and GaP in PH 3 and NH 3 , respectively, are investigated, and metalorganic chemical vapor deposition (MOCVD) growth of GaP on GaN and GaN on GaP was performed. The following results are obtained: N atoms are introduced into GaP by the annealing in NH 3 at relatively low temperature of about 800°C and wurtzite-GaN crystal is formed. However, the GaN crystal quality is low and GaP is degraded. On the other hand, high temperature annealing is necessary to introduce P atoms into GaN by the annealing in PH 3 . The heteroepitaxy of hard GaN on GaP degrades substrate quality, and the reverse epitaxy, soft GaP on hard GaN substrate, is greatly influenced by the substrate quality.

Growth mechanism of AlGaAs on terraced substrates by low pressure MOVPE

AlGaAs layers were grown on recessed GaAs substrates by MOVPE at 5 and 100 Torr. The two mechanisms, the gas phase diffusion through the stagnant layer and the surface migration of the growing species, are responsible for the surface step height after the growth. Since the mean free path in the gas phase at 5 Torr (≈20μm) is longer than the recess height (≈1μm), only the surface migration determines the growth at 5 Torr, while both mechanisms contribute to the growth at 100 Torr. The surface diffusion equation is solved to find out the relation between the growth conditions and the surface step height after the growth. It was found that the surface migration length on the (111)A surface is much longer than that on the (100) plane. The optical waveguide is fabricated by growing a double-heterostructure on the recessed substrate, and light confinement in the channel is verified.

MOCVD GROWTH OF GaN ON III-V, Si and GaAs-COATED-Si SUBSTRATES

Abstract This paper describes the first MOCVD growth of GaN on Si substrate whose surface is covered by crystalline GaAs. Since bulk modulus of GaAs is smaller than those of GaN and Si, more dislocation is expected to be formed in GaAs than in GaN. GaAs on (100) 4°off Si, pure Si(100), and GaP (100), (111) are used as substrates. Much improvement is obtained by coating Si substrate by crystalline GaAs. The effects of the substrate and the surface preparation are discussed.

A New Reactor for Metalorganic Chemical Vapor Deposition Equipped with an Internal Rotary Flow Selector

A reactor for metalorganic chemical vapor deposition is newly developed. The reactor has an internal flow selector by which two out of four continuously flowing gases are selected. The gas switching is performed just by rotating the flow selector without turning the valves on and off, eliminating the valve lifetime problem. The reduced effective reactor volume enables rapid gas switching at a relatively fast growth rate. GaAs/AlAs quantum wells are grown to check the gas switching ability. The cross-sectional transmission electron microscopy (TEM) image clearly shows 30-, 50- and 100 ?-thick quantum well structures, as expected.