Blue-green and white color tuning of monolithic light emitting diodes

Abstract

A blue light emitting diode (LED) is grown on top of a (Ga, In)N/GaN multiple quantum well (QW) acting as a light converter from blue to green-yellow wavelength. The blue light is produced by electrical injection, while the green-yellow emitting QWs are optically pumped by the blue photons. It is shown that the final color of the LED is strongly dependent on the blue pumping wavelength, the absorption and the internal quantum efficiency of the light converter. Depending on these parameters, blue to green LEDs or even white LEDs can be obtained. In addition, the injection current dependence of the LED electroluminescence is measured and analyzed. A very low blueshift is observed as a function of the injection current. It is explained by the fact that the carrier density per QW in the light converter stays relatively low compared to the case of classical current-injected green LEDs.

Di-Chromatic InGaN Based Color Tuneable Monolithic LED with High Color Rendering Index

“…In addition, since the passive QWs are designed to operate on the green gap spectral range they being less efficient than phosphor for that range and their sensitivity to active QW emission wavelength is a disadvantage [18]. The best CRI for such devices reported is 41 [16]. White light emission from all electrically pumped QWs with CCT∼6000 K has been reported previously [19].…”

“…A simpler fabrication approach of vertically stacked QWs emitting at two distinct wavelengths has been reported. Active region of such devices can consist of either: (i) longer wavelength emitting passive QWs pumped by active blue QW [16]; or (ii) all electrically pumped active QWs [8,11,17]. The first approach is similar to phosphor covered LEDs and the spectrum is controlled by number of passive QWs in active region.…”

Luminescence properties of InGaN‐based dual‐wavelength light‐emitting diodes with different quantum‐well arrangements

“…Although these white LED devices reach large luminous efficiencies, the addition of the phosphor complicates the LED process which in turn increases the LED manufacturing cost and optical absorption [6][7][8]. Therefore, "phosphor free" or "monolithic" white LEDs have been proposed [9,10].…”

Monolithic phosphor-free InGaN/GaN quantum dot wavelength converter white light emitting diodes

“…1,2 Monolithic planar white LEDs consisting of InGaN/GaN quantum wells, based on both direct electrical injection 3-7 as well as optical pumping in a converter scheme, 8 have been reported. Since long wavelength LEDs (k > 600 nm) with III-nitride quantum well active regions are still in a developmental stage, the most common approach for realizing a solid state white LED is to either have a blueemitting LED optically pump yellow phosphor 9,10 or have an ultraviolet (UV) LED excite rare earth doped blue-, green-, and red-emitting phosphors.…”