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The compliant behavior of densely packed 10 × 10 µm2 square patterned InGaN layers on top of porous GaN is demonstrated. The elastic relaxation of the InGaN layers is enabled by the low stiffness of the porous GaN under layer. High resolution X-ray diffraction measurements show that upon InGaN re-growths on these InGaN-on-porous GaN pseudo-substrates, not only was the regrown layer partially relaxed, but the degree of relaxation of the InGaN pseudo-substrate layer on top of the porous GaN also showed an increase in the a-lattice constant. Furthermore, methods to improve the surface morphology of the InGaN layers grown by metal-organic chemical vapor deposition (MOCVD) were explored in order to fabricate InGaN pseudo-substrates for future optoelectronic and electronic devices. The largest a-lattice constant demonstrated in this study using this improved method was 3.209 Å, corresponding to a fully relaxed InGaN film with an indium composition of 0.056.

Time-resolved photoluminescence measurements have been performed on Mg-doped GaN for Mg concentrations in the low- to mid-1019 cm−3. As-grown and annealed (600–675 °C) samples were studied. In the as-grown samples, the nonradiative carrier lifetime was found to be about 200 ps and nearly independent of the Mg concentration. Upon annealing, the carrier lifetimes shorten to ∼150 ps but, again, show little dependence on the annealing temperature. The analysis of possible Shockley–Read–Hall recombination centers and their behavior during doping and annealing suggests that the main nonradiative recombination center is the Mg–nitrogen vacancy complex. The weak dependence of the PL decay times on temperature indicates that carrier capture into this center has a very low potential barrier, and the nonradiative recombination dominates even at low temperatures. [ABSTRACT FROM AUTHOR]

The efficiency of high-power operation of multiple quantum well (QW) light emitting diodes (LEDs) to a large degree depends on the realization of uniform hole distribution between the QWs. In long wavelength InGaN/GaN QW LEDs, the thermionic interwell hole transport is hindered by high GaN barriers. However, in polar LED structures, these barriers may be circumvented by the lateral hole injection via semipolar 10 1 ¯ 1 QWs that form on the facets of V-defects. The efficiency of such carrier transfer depends on the transport time since transport in the semipolar QWs is competed by recombination. In this work, we study the carrier transfer from the semipolar to polar QWs by time-resolved photoluminescence in long wavelength (green to red) LEDs. We find that the carrier transfer through the semipolar QWs is fast, a few tens of picoseconds with the estimated room temperature ambipolar diffusion coefficient of ∼5.5 cm2/s. With diffusion much faster than recombination, the hole transport from the p-side of the structure to the polar QWs should proceed without a substantial loss, contributing to the high efficiency of long wavelength GaN LEDs. [ABSTRACT FROM AUTHOR]

Investigations of the use of patterned porous GaN underlayers to achieve elastic relaxation of lattice‐mismatched top layers such as InGaN and AlGaN are reviewed. Thereby, the degree of relaxation of the top layers increases with the porosity and associated decrease in mechanical hardness of the porous GaN underlayers as well as with decreasing pattern size and increase in thickness of the lattice‐mismatched top layers, following the trends observed for nanostructures. Micrometer‐sized, high‐fill‐factor GaN‐on‐porous‐GaN tile arrays are used as universal substrate for the deposition of InGaN and AlGaN. Due to the elastic nature of the relaxation process, the threading dislocation density in the epitaxial material grown on top of the GaN‐on‐porous‐GaN tiles is equivalent to that in the GaN base material. InGaN and AlGaN layers grown on top of relaxed or partially relaxed InGaN or AlGaN underlayers by metal–organic chemical vapor deposition display a higher indium or aluminum content compared to their counterparts deposited on coloaded planar GaN reference wafers due to the decreased lattice mismatch. First applications of the patterned porous GaN‐based technology for optoelectronic and electronic devices are presented and serve as a pathway toward future implementations. [ABSTRACT FROM AUTHOR]

Crack-free 1.3 μm thick elastically relaxed AlxGa1−xN layers were demonstrated on compliant high fill-factor 10 × 10 μm2 tile patterned GaN-on-porous-GaN pseudo-substrates (PSs). Porous GaN was utilized as a semi-flexible underlayer. The AlxGa1−xN layer was grown in steps of 200, 300, 400, and 400 nm. While the AlxGa1−xN layer regrown on a co-loaded GaN-on-sapphire template cracked after deposition of only 200 nm AlGaN, on the GaN-on-porous GaN patterned substrates, no cracks were observed, and smooth films were achieved. In addition, an enhanced aluminum uptake was observed as the AlGaN growth progressed on the GaN-on-porous-GaN PS, owing to the composition pulling effect, until the point when the tiles started to coalesce. Upon further regrowth on these coalesced tiles, the aluminum uptake saturated, while the surface remained crack-free and smooth. [ABSTRACT FROM AUTHOR]

The author discusses the story behind the invention of blue light-emitting diode .Topics include the progress made in combining white LED to blue LED using yellow phosphor, the material properties of indium gallium nitride as well as metal organic chemical vapor deposition as candidates for the development of blue LED and the future challenges of blue LED in the field of electronic. The author Shuji Nakamura, a Japanese physicist and the inventor of blue LED presents his autobiography.

Devices grown on nonpolar and semipolar planes of GaN offer key performance advantages over devices grown on the conventional c-plane, including reduced polarization fields. This allows for a wider design space on semipolar planes for light emitting diodes (LEDs) to address the problem of efficiency droop at high current densities. LED structures with very thick (10-100 nm) InGaN single-quantum-well/double heterostructure active regions were grown using conventional metal organic chemical vapor deposition on semipolar (3031) free-standing GaN substrates and processed and packaged using conventional techniques. Simulated band diagrams showed reduced polarization fields on the (3031) plane. The calculated critical thickness for misfit dislocation formation is higher on the (3031) plane than on other semipolar planes, such as (2021), allowing for thicker active regions than our previous work to further reduce droop. The higher critical thickness was confirmed with defect characterization via cathodoluminescence. A trend is demonstrated in lower efficiency droop for devices with thicker active regions. Thermal droop characteristics of these devices are also presented. These observed results were utilized to demonstrate over 1W of output power at a current density of 1 kA/cm² from a single 0.1mm² LED device. [ABSTRACT FROM AUTHOR]