Realization of high-luminous-efficiency InGaN light-emitting diodes in the "green gap" range

Light-emitting diodes (LEDs) in the wavelength region of 535-570 nm are still inefficient, which is known as the "green gap" problem. Light in this range causes maximum luminous sensation in the human eye and is therefore advantageous for many potential uses. Here, we demonstrate a high-brightness InGaN LED with a normal voltage in the "green gap" range based on hybrid multi-quantum wells (MQWs). A yellow-green LED device is successfully fabricated and has a dominant wavelength, light output power, luminous efficiency and forward voltage of 560 nm, 2.14 mW, 19.58 lm/W and 3.39 V, respectively. To investigate the light emitting mechanism, a comparative analysis of the hybrid MQW LED and a conventional LED is conducted. The results show a 2.4-fold enhancement of the 540-nm light output power at a 20-mA injection current by the new structure due to the stronger localization effect, and such enhancement becomes larger at longer wavelengths. Our experimental data suggest that the hybrid MQW structure can effectively push the efficient InGaN LED emission toward longer wavelengths, connecting to the lower limit of the AlGaInP LEDs' spectral range, thus enabling completion of the LED product line covering the entire visible spectrum with sufficient luminous efficacy.