Flower-Like Internal Emission Distribution of LEDs with Monolithic Integration of InGaN-based Quantum Wells Emitting Narrow Blue, Green, and Red Spectra

Abstract

We report a phosphor-free white light-emitting diodes (LED) realized by the monolithic integration of In0.18Ga0.82N/GaN (438 nm, blue), In0.26Ga0.74N/GaN (513 nm, green), and In0.45Ga0.55N/In0.13Ga0.87N (602 nm, red) quantum wells (QWs) as an active medium. The QWs corresponding to blue and green light were grown using a conventional growth mode. For the red spectral emission, five-stacked In0.45Ga0.55N/In0.13Ga0.87N QWs were realized by the so-called Ga-flow-interruption (Ga-FI) technique, wherein the Ga supply was periodically interrupted during the deposition of In0.3Ga0.7N to form an In0.45Ga0.55N well. The vertical and lateral distributions of the three different light emissions were investigated by fluorescence microscope (FM) images. The FM image measured at a focal point in the middle of the n-GaN cladding layer for the red-emitting LED shows that light emissions with flower-like patterns with six petals are periodically observed. The chromaticity coordinates of the electroluminescence spectrum for the white LEDs at an injection current of 80 mA are measured to be (0.316, 0.312), which is close to ideal white light. In contrast with phosphor-free white-light-emitting devices based on nanostructures, our white light device exhibits a mixture of three independent wavelengths by monolithically grown InGaN-based QWs, thus demonstrating a more facile technique to obtain white LEDs.

State-of-the-art and prospects for intense red radiation from core–shell InGaN/GaN nanorods

“…The alternative approach implies that the active region includes InGaN inserts -quantum wells, disks, or dots of various width/composition/polarity designed to cover the entire visible range together. This approach dominates up to now [3,[16][17][18][19][20][21][22][23][24]. It is worth mention that the increase in the number of QWs when all of them are pumped electrically does not mean a proportional increase in electroluminescence (EL) intensity because of the limitation of carrier injection and transport [25,26].…”

Application of Hexagonal Boron Nitride to a Heat-Transfer Medium of an InGaN/GaN Quantum-Well Green LED

“…At an injection current of 120 mA, the light power was measured as 38.9 mW. More details related to the optical characteristics of InGaN/GaN-QW LEDs are described in our previous reports. , …”

“…More details related to the optical characteristics of InGaN/GaN-QW LEDs are described in our previous reports. 30,31 When an LED is driven, its device performances are largely affected by the ambient temperature as well as the heat components generated within the chip during its operation. To evaluate the influence of the hBN sheet on the heat-transfer characteristics of the hBN-LED, DSC experiments were first conducted by changing the ambient temperature.…”

“…Indium-tin-oxide with a thickness of 150 nm was deposited as a transparent conducting layer on the p-GaN cladding layer, and Cr/Au was deposited as the n- and p-type electrodes, respectively. The growth conditions and structural properties of InGaN/GaN-QW LEDs are described in detail in our previous reports. − …”

High-color-rendering-index phosphor-free InGaN-based white light-emitting diodes by carrier injection enhancement via V-pits

“…By tuning the alloy composition of III-nitride materials, they can be made to emit over the full visible spectrum, which makes them excellent candidates for monolithically integrated white LEDs with polychromatic emission. Researchers have proposed several approaches to produce monolithic, phosphor-free InGaN-based white LEDs, such as multiple quantum wells (MQWs) with different emission wavelengths, [5][6][7][8] nanorod array structures, [9][10][11] quantum dot structures, 12,13 patterned microstructures, [14][15][16][17] and optically pumped QWs. 18,19 In particular, LED fabrication requires a simplified process that does not involve phosphors or patterned nano or microstructures.…”