Indium gallium nitride (InGaN)-based light-emitting diodes (LEDs) are considered a promising candidate for red-green-blue (RGB) micro displays. Currently, the blue and green LEDs are efficient, while the red ones are inefficient for such applications. This paper reports our work of creating efficient InGaN-based orange and red LEDs on silicon(111) substrates at low current density. Based on the structure of InGaN yellow LEDs, by simply reducing the growth temperature of all the yellow quantum wells (QWs), we obtained 599 nm orange LEDs with peak wall-plug efficiency (WPE) of 18.1% at
2
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cm
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. An optimized QW structure was proposed that changed two of the nine yellow QWs to orange ones. Compared with the sample containing nine orange QWs, the sample with two orange QWs and seven yellow QWs showed similar emission spectra but a much higher peak WPE up to 24.0% at
0.8
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with a wavelength of 608 nm. The improvement of peak WPE can be attributed to the improved QW quality and the reduced active recombination volume. Subsequently, a series of efficient InGaN-based orange and red LEDs was demonstrated. With further development, the InGaN-based red LEDs are believed to be attainable and can be used in micro LED displays.
Inhomogeneous electroluminescence (EL) of InGaN green LEDs grown on mesh-patterned Si (111) substrate had been investigated. Sample with n-AlGaN inserted between the pre-strained layers and the first quantum well showed the inhomogeneous EL in the low current density range. Near-field EL emission intensity distribution images depicted that inhomogeneity in the form of premature turn-on at the periphery of the LED chip, results in stronger emission intensity at the edges. This premature turn-on effect significantly reduces the luminous efficacy and higher ideality factor value due to locally current crowding effect. Raman measurement and fluorescence microscopy results indicated that the partially relaxed in-plane stress at the edge of the window region acts as a parasitic diode with a smaller energy band gap, which is a source of edge emission. Numerical simulations showd that the tilted triangular n-AlGaN functions like a forward-biased Schottky diode, which not only impedes carrier transport, but also contributes a certain ideality factor.
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