We present principle of defect characterization of GaN using multiphoton-excitation photoluminescence and several experimental results. Threading dislocations and basal plane dislocations in n-type GaN are observed from near-band-edge emission imaging. The diameters of dark spots and dark lines are determined by the minority carrier diffusion length. Three-dimensional feature of dark lines is different by the Burgers vectors of dislocations. Based on these properties, nondestructive classification of dislocations is possible. Simultaneous detection of near-band-edge emission and yellow luminescence can be utilized to visualize three-dimensional growth processes such as facet-initiated epitaxial lateral overgrowth, which is used to obtain GaN substrates with low threading dislocation densities.
Two types of novel wavelength conversion device structure are proposed: a transverse quasi-phase matched waveguide and a monolithic microcavity. The former includes polarity-inverted stacked multilayer of AlN or GaN artificially fabricated by wafer bonding or epitaxial polarity inversion techniques. And the latter is a microcavity composed of a GaN domain with one coherence length sandwiched with two DBRs. The report on the successful demonstration of second harmonic generation and the discussion on the exploration for the novel nonlinear optical materials, even in the absence of birefringence and ferroelectricity, will be given in the presentation.
The behavior of threading dislocations and stacking faults were investigated in a (1-101) GaN grown on a patterned
(001)Si substrate by selective metal-organic-vapor-phase-epitaxy with an AlN buffer layer. Cross sectional transmission
electron microscopy images showed that threading dislocations are generated at the hetero-interface of GaN/AlN/Si
induced by misfit dislocations, while stacking faults are generated when two crystals with different crystal axes coalesce. We found some of them are annihilated making a loop, where two stacking faults have been generated at a short distance. This suggests a rout to decrease the density of stacking faults in III nitrides.
We present a study of semi-polar (1-101) InGaN-based light emitting diodes (LEDs) grown on
patterned (001) Si substrates by atmospheric-pressure metal organic chemical vapor deposition. A
transmission electron microscopy image of the semi-polar template shows that the threading
dislocation density was decreased significantly. From electroluminescence measurement,
semi-polar LEDs exhibit little blue-shift and low efficiency droop at a high injection current
because the reduction of the polarization field not only made the band diagram smoother but also
restricted electron overflow to the p-GaN layer as shown in simulations. These results indicate that
semi-polar InGaN-based LEDs can possess a high radiative recombination rate and low efficiency
droop at a high injection current.
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