Flower-like light distribution inside InGaN-based light-emitting diodes operated in spectral range from violet to red

Nowadays, phosphor-based light-emitting diodes (LEDs) with InGaN/GaN quantum wells (QWs) are commonly used for white light sources [1]. However, degradation of phosphor material during long-term optical pumping is inevitable, resulting that output efficiency and color-rendering index of white LEDs are significantly reduced. Therefore, a phosphor-free white LED realized by directly mixing three primary colors is considered as a good alternative to improve device performances. For the fabrication of phosphor-free white LEDs using InGaN-based QWs, the growth of InGaN emitting in the wavelength above ~550 nm is currently required. To extend the emission wavelength of InGaN to red spectral range, indium (In) content should be increased. However, it is difficult to grow high-quality InGaN with high In content mainly due to intrinsic phase separation of InN and GaN [2]. In this work, we report device characteristics of yellow-red LEDs, where the active InGaN-based QWs were prepared by a new growth technique. And then, the lateral and vertical light distribution inside the LEDs operated in the spectral range from violet to red will be discussed with theoretical analysis. We also present phosphor-free white LEDs realized by monolithic integration of InGaN-based QWs emitting narrow blue, green, and red spectra.