The surface plasmon (SP) resonance was used to increase the emission efficiencies toward high efficiency light-emitting diodes (LEDs). We obtained the enhancements of the electroluminescence from the fabricated plasmonic LED device structure by employing the very thin p+-GaN layer. The further enhancements should be achievable by optimization of the metal and device structures. Next important challenge is to extend this method from the visible to the deep UV region. By using Aluminum, we obtained the enhancements of emissions at ~260 nm from AlGaN/AlN quantum wells. We succeeded to control the SP resonance by using the various metal nanostructures. These localized SP resonance spectra in the deep-UV regions presented here would be useful to enhance deep UV emissions of super wide bandgap materials such as AlGaN/AlN. We believe that our approaches based on ultra-deep UV plasmonics would bring high efficiency ultra-deep UV light sources.
This paper presents the growth of thick semipolar {10-11}, {11-22}, and {20-21} GaN layers on n, r, and {22-43} patterned sapphire substrates (PSSs), respectively, by hydride vapor phase epitaxy. The reduction rate of the dislocation density varied with growth planes. For {10-11} GaN layers, the dislocation density drastically decreased at over 100 μm, which was as fast the reduction rate as in the case of the c-plane. It was revealed that the reduction rate of the dislocation density could be controlled by the proper selection of the growth plane. We obtained a freestanding GaN of 2 inch diameter. Thick GaN growth led to the self-separation of the GaN layer from the PSS during cooling process. The separation plane formed at the interface between GaN and PSS, which is different from the case of a conventional c-plane GaN/sapphire. The separationability of the GaN layer from the PSS depended on the selective growth area of the sapphire sidewall.
The light-emitting diodes (LEDs) with high external quantum efficiency (EQE) are usually fabricated on the
patterned sapphire substrate (PSS). The PSS reduces the dislocation density in the GaN layer and enhances the light
extraction efficiency (LEE) from the LED chip by scattering the light confined in GaN layer attributed to the critical
angle between GaN (n=2.4) and sapphire substrate (n=1.7) (or air (n=1.0)). On the other hand, non-polar GaN and semipolar
GaN are attracted much attention to eliminate the quantum confined Stark effect (QCSE). Recently, we have
developed novel technology to grow non-polar or semi-polar GaN on the PSS with high quality and large diameter by
metal-organic vapor phase epitaxy (MOVPE). For example, m-plane GaN grown on a-plane PSS and {112 (see manuscript)} plane GaN
grown on r-plane PSS. The growth of c-plane GaN from the c-plane-like sidewall of the r-plane PSS results in {112 (see manuscript)}
GaN on the r-plane PSS. The full widths at half maximum of X-ray rocking curves (FWHM-XRC) of the {112(see manuscript)} GaN
along the azimuths parallel and perpendicular to the c-direction were 533 and 260 arcsec, respectively. Dislocation
density of the GaN was approximately 2×108 cm-2. These non-polar and semi-polar GaN are expected to be suitable for
novel GaN substrate or GaN template for LEDs.
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