Yuhzoh Tsuda

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.

Blue-Violet Inner Stripe Laser Diodes Using Lattice Matched AlInN as Current Confinement Layer for High Power Operation

We report on a novel method using lattice matched AlInN as the current confinement layer for inner stripe laser diodes. Optimisation of the sample preparation techniques and metal organic chemical vapor deposition (MOCVD) regrowth conditions resulted in an inner stripe laser diode with threshold current density of ~3.3–3.5 kA/cm2 and slope efficiency of 1.6 W/A. The cw lifetime and other characteristics of the inner stripe laser diode are discussed. Simulation data have also shown that this structure is beneficial for reducing operating voltage when compared to a conventional ridge waveguide structure.

Structural and optical properties of GaN1−xAsx grown by metalorganic chemical vapor deposition

GaN-based GaN1−xAsx alloys, x⩽0.043, were grown by metalorganic chemical vapor deposition. The results of high-resolution x-ray diffraction measurements indicated that no phase separation was observed over a range of up to x=0.043 and both the lattice constants c and a increased with an increase in arsenic composition. In cathodoluminescence measurements, the GaN1−xAsx showed a large band gap bowing parameter of 22.1eV. Furthermore, we have experimentally revealed that the valence band offset for the GaN1−xAsx∕GaN is very large, and we have proposed the band gap energy diagram of GaN1−xAsx utilizing an arsenic deep donor level.

GaN strain reduction by growth on compliant GaN-rich GaNP

For investigating the strain reduction in a GaN layer on a sapphire substrate, double heterostructures of the upper GaN layer/GaN-rich GaNP interlayer as a compliant buffer layer/lower GaN layer were grown by metalorganic chemical vapor deposition. It has been confirmed that wafer bending of the double heterostructure reduces on increasing the mole fraction of phosphorus incorporated into GaNP. Further, the results of x-ray diffraction and Raman scattering analysis revealed that strain relaxation occurs abruptly on the GaNP interlayer and that nonuniform distortion of the upper GaN layer scarcely distributes within the thickness.

Analysis of the GaN-rich side of GaNP using x-ray diffraction

We investigated the growth of the GaN-rich side of GaNP films using metal-organic chemical-vapor deposition. The results of Auger electron spectroscopy suggest that phosphorus atoms incorporated into the film would be substituted on gallium sites rather than on nitrogen sites. Using x-ray diffraction, we have revealed that such GaNP films belong to a hexagonal system and that the relationship of the orientation between the GaNP film and its underlying GaN layer is [0001]GaNP‖[0001]GaN and [101¯0]GaNP‖[101¯0]GaN. Moreover, it was found that the lattice constants of GaNP were smaller than those of bulk GaN and there was no phase separation. We have also confirmed that the changes in these lattice constants were almost proportional to the phosphorus concentration included in the entire GaNP film thickness and that they decreased with an increase in the phosphorus concentration.