Liquid crystalline Blue Phases have recently encouraged a large interest in soft matter materials development, due to their possible application in faster and easier to produce displays. One of the principal difficulties of exploiting Blue Phases in general is the fact that they are frustrated phases, normally only occurring in small temperature regimes, well above room-temperature. We present a variety of mechanisms to stabilize Blue Phases, and discuss their physical mechanisms and effectiveness. This covers conventional methods such as chiral doping, bent-core doping, polymer stabilization, all the way to nano-particle doping, nanotube dispersions, and combinations of all of the above. It appears that the stabilization mechanism is very sensitive to the applied conditions, thus optimization is an important factor. We observed the best results for hybrid systems with (i) polymer stabilized bent core doped Blue Phases, and (ii) nanoparticle plus bent core doped Blue Phases.

Photoluminescence and electroluminescence measurements on InGaN/GaN quantum well (QW) structures and light emitting diodes suggest that QWs with gross fluctuations in width (formed when, during growth, the InGaN is exposed unprotected to high temperatures) give higher room temperature quantum efficiencies than continuous QWs. The efficiency does not depend on the growth temperature of the GaN barriers. Temperature-dependent electroluminescence measurements suggest that the higher efficiency results from higher activation energies for defect-related non-radiative recombination in QW samples with gaps. At high currents the maximum quantum efficiency is similar for all samples, indicating the droop term is not dependent on QW morphology.

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This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.High resolution transmission electron microscopy has been employed to investigate the impact of the GaN barrier growth technique on the composition profile of InGaN quantum wells (QWs). We show that the profiles deviate from their nominal configuration due to the presence of an indium tail at the upper interface of the QW. This indium tail, thought to be associated with a segregation effect from the indium surfactant layer, has been shown to strongly depend on the growth method. The effect of this tail has been investigated using a self-consistent Schrödinger-Poisson simulation. For the simulated conditions, a graded upper interface has been found to result in a decreased electron-hole wavefunction overlap of up to 31% compared to a QW with a rectangular profile, possibly leading to a decrease in radiative-recombination rate. Therefore, in order to maximize the efficiency of a QW structure, it is important to grow the active region using a growth method which leads to QW interfaces which are as abrupt as possible. The results of this experiment find applications in every study where the emission properties of a device are correlated to a particular active region design.