When lattice matched to GaN, the AlInN ternary alloy has a refractive index ∼7% lower than that of GaN. This characteristic can be exploited to perform in situ reflectometry during epitaxial growth of GaN-based multilayer structures on free-standing GaN substrates, by insertion of a suitable Al0.82In0.18N layer. The real-time information on growth rates and cumulative layer thicknesses thus obtainable is particularly valuable in the growth of optical resonant cavity structures. We illustrate this capability with reference to the growth of InGaN∕GaN multiple quantum-well structures, including a doubly periodic structure with relatively thick GaN spacer layers between groups of wells. Al0.82In0.18N insertion layers can also assist in the fabrication of resonant cavity structures in postgrowth processing, for example, acting as sacrificial layers in a lift-off process exploiting etch selectivity between Al0.82In0.18N and GaN.
The integration of arrays of 486nm-emitting micron-size LEDs onto non-native substrates (including diamond, ultra-thin glass and MQW epitaxial structures) is demonstrated. The device bonding process relies solely on solvent-assisted capillary adhesion, and precision assembly through transfer printing.
We report on the influence of surface-related states on the relaxation of carriers within single (Ga,In)N/GaN quantum wells. Two identical samples that differ only in the thickness of the top GaN cap layer were studied. Photoluminescence and pump-probe measurements reveal significant variations in the quantum well integrated emission and the carrier relaxation decay times in the two samples, when probing both the ground and excited states of the wells. The variations are attributed to the presence of an efficient nonradiative relaxation channel associated with the proximity of the quantum well excitations to the surface-related states in the thin-cap sample.
Carrier dynamics in metal-semiconductor structures is driven by electrodynamic coupling of carriers to the evanescent field of surface plasmons. Useful modifications in electron and hole dynamics due to presence of metallic inclusions show promise for applications from light emitters to communications. However, this picture does not include contributions from electrostatics. We propose here an electrostatic mechanism for enhancement of light radiated from semiconductor emitter which is comparable in effect to plasmonic mechanism. Arising from Coulomb attraction of e-h pairs to their electrostatic images in metallic nanoparticles, this mechanism produces large carrier concentrations near the nanoparticle. A strong inhomogeneity in the carrier distribution and an increase in the internal quantum efficiency are predicted. In our experiments, this manifests as emission enhancement in InGaN quantum well (QW) radiating in the near-UV region. This fundamental mechanism provides a new perspective for improving the efficiency of broadband light emitters.
Gallium-Nitride-based light-emitting diodes (LEDs) have emerged over the last two decades as highly energy-efficient, cost-effective, compact and robust light sources. While general purpose lighting has been the dominant application thus far, a variety of other applications can also exploit these advantageous properties, including optical communications, fluorescence sensing and bioscience. Micro-LEDs arrays of individually-addressable LED pixels, each pixel typically 100 µm or less, offer further advantages over conventional LEDs such as extremely high modulation bandwidths and spatio-temporally controllable illumination patterns. These arrays are also readily compatible with flip-chip integration with CMOS electronic driver arrays. Here we report how these CMOS-controlled micro-LED arrays enable “smart lighting” solutions, capable of providing services such as wireless data communication and indoor navigation in conjunction with illumination. We also demonstrate how this smart functionality opens up novel bioscience applications, including depth-specific in-vivo optical neural probes and wireless transfer of measured data.
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