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InGaN-based micro-light-emitting diodes have a strong potential as a crucial building block for next-generation displays. However, small-size pixels suffer from efficiency degradations, which increase the power consumption of the display. We demonstrate strategies for epitaxial structure engineering carefully considering the quantum barrier layer and electron blocking layer to alleviate efficiency degradations in low current injection regime by reducing the lateral diffusion of injected carriers via reducing the tunneling rate of electrons through the barrier layer and balanced carrier injection. As a result, the fabricated micro-light-emitting diodes show a high external quantum efficiency of 3.00% at 0.1 A/cm2 for the pixel size of 10 × 10 μm2 and a negligible Jmax EQE shift during size reduction, which is challenging due to the non-radiative recombination at the sidewall. Furthermore, we verify that our epitaxy strategies can result in the relaxation of self-heating of the micro-light-emitting diodes, where the average pixel temperature was effectively reduced.

The paper presents the assessment of equivalence of the spectral radiance scales in the wavelength range from 250 to 2500 nm, reproduced at the national metrology institutes of Korea (KRISS), China (NIM), and Russia (VNIIOFI), carried out in the framework of international comparisons. The common set of three tungsten strip lamps was used as an artefact. Based on a series of blind measurements of the lamps spectral radiance performed at each laboratory alternately, the reference value of the comparison was determined at each wavelength as a weighted mean of the measured data of three laboratories. The degree of equivalence of each laboratory was then calculated as the deviation of the measurement data of that participant from the reference value. A data analysis method was proposed for calculating the degree of equivalences and their uncertainties. The method is based on processing spectral radiance ratios, rather than differences, which allows eliminating the influence of a result of one particular participant to results of other laboratories. The comparison results confirm the equivalence of spectral radiance scales of all the laboratories within their expanded uncertainties (k = 2) except a few wavelength points.

We report on a self-guided operation of a green-pumped singly resonant continuous-wave optical parametric oscillator with a bulk MgO-doped PPLN crystal. It is achieved by increasing the OPO cavity length beyond the stability boundary so that the OPO can only oscillate with formation of a thermally induced waveguide inside the crystal. The effects of the thermal waveguide on the OPO performance are studied by measuring output power characteristics at different cavity lengths. Improvement of spatial mode quality and stability of output power by self-guiding is demonstrated. Measurement of temporal characteristics proves that formation of the waveguide originates from the photo-thermal effect in the nonlinear crystal by absorption of pump power.