Continuous-wave operation at room-temperature has been demonstrated for
InGaN multi-quantum-well (MQW) laser diodes (LDs) grown on
low-dislocation-density n-GaN substrates with a backside n-contact. The
current, current density and voltage at the lasing threshold were 144 mA,
10.9 kA/cm2 and 10.5 V, respectively, for a 3 µm wide ridge-geometry diode
with high-reflection dielectric coated mirrors. Single-transverse-mode
emission was observed in the far-field pattern of the LDs and the beam full
width at half power in the parallel and perpendicular directions was 6° and
25°, respectively.
X-ray rocking curve measurements have been carried out in order to investigate the
twisting and tilting in hydride vapor phase epitaxy (HVPE) and metalorganic vapor
phase epitaxy (MOVPE) GaN films fabricated by an epitaxial lateral overgrowth (ELO)
technique. The twist angle is directly determined by means of grazing incidence angle
X-ray diffraction. It is found that these angles in both MOVPE and HVPE films are
significantly reduced by the ELO technique especially for the twist angles. In the
MOVPE-ELO GaN film, the tilt and twist angles depend on the stripe direction of the
mask pattern, which is closely related to the difference of the growth process.
Dislocation propagation and defect evolution in GaN films formed by epitaxial lateral overgrowth (ELO) are examined by transmission electron microscopy. A novel effect that induces self-organized propagation of preexisting dislocations in ELO films is evaluated. This propagation forms dislocations into bundle structures along the stripes of masks used for ELO. The dislocation bundling gives rise to crystallographic tilting in the overgrown region on the mask and leads to a total reduction of threading dislocation density in the film.
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