The size-dependent variation of external-quantum-efficiency (EQE) has investigated by fabricating InGaN-based blue and near ultraviolet (NUV) micro light-emitting diodes (μ-LEDs) with mesa sizes from 10×10 μm2 to 250×250 μm2. We have compared the performances between blue and NUV μ-LEDs by measuring various optoelectronic characteristics, and found opposite trend between them. With reducing μ-LED sizes, the EQE of blue μ-LEDs decreases due to temperature-dependent efficiency droop which is consistently obtained by calculating the blueshift in peak-wavelengths and thermal-resistance. Contrary, the improved current spreading increases the light-extraction-efficiency which causes the EQE of small sized NUV μ-LEDs to increase.
We have fabricated InGaN/GaN multiple-quantum-well flip-chip blue ultrathin side-emitting (USE) light-emitting diode (LED) by top and bottom mirrors and investigated the sidewall light emission performances for backlight unit. Fabricated USE-LED has uniform light-output-power (LOP) and peak wavelength characteristics at each sidewall except poor light extraction efficiency (LEE) which is improved by fabricating ZnO nanorods on each sidewall. The optimized nanorods improve the LEE of USE-LED. Thus, the LOP increases >80% compared to the Reference-LED. Furthermore, the light-tools simulation results reveal that the LEE of nanorods-based USE-LED increases in lateral direction due to decrease in internal reflection of light.
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