Indium Localization‐Induced Red, Green, and Blue Emissions of Semipolar (11‐22) GaN‐Based Light‐Emitting Diodes

Abstract

Red, green, and blue electroluminescence (EL) in semipolar (11-22) GaN-based light-emitting diodes (LEDs) is achieved using SiO 2 hexagonal patterns epitaxial lateral overgrowth (HP-ELO). The size, density, and area of arrowhead-like surface structure of the semipolar (11-22) HP-ELO GaN are significantly affected by increasing the SiO 2 hexagonal patterns from 6.0 to 15.0 μm. The full width at half maximum and the blueshift wavelength of EL spectra increases with increasing from 6.0 to 9.0 μm, and then decreases with increasing the hexagonal pattern width to 15.0 μm. These results show a similar tendency to the surface area of arrowhead-like structure. In addition, micro-EL images show that indium localization-induced low energy emission initiates at the front end of arrowheadlike pattern, and then blueshifted emissions propagate to the side edges as the injection current increases. Therefore, it suggests that HP-ELO can control the arrowhead-like surface structure composed of different indium compositions, which can achieve red, green, and blue emissions of a semipolar (11-22) HP-ELO GaN-based LED.

Microdisk-Type Multicolor Semipolar Nitride-Based Light-Emitting Diodes

“…The detailed changes in the emission spectra for SQ- and MD-LEDs with different sizes are exhibited in Figures S4a. It is known that the arrowhead-like surface structure consists of a few crystal planes that have different indium incorporations, leading to a strong blue shift in the emission wavelength (from amber to violet) because of the band-filling effect, as shown in Figure S4b. Therefore, the emission wavelength of the semipolar GaN-based MD-LEDs could be controlled from amber to violet by decreasing their diameter and increasing the injection current density, as shown in Figure c. These results suggest that fully wet-etched semipolar MD-LEDs can be applied to the full-color pixels source of micro-LED displays and the multiple colors microlighting applications using only one semipolar LED wafer.…”

“…As the same operating current of 1.0 mA was applied, the injection current density of the LEDs increased significantly with a decrease in their size. Therefore, the emission of the LEDs showed a blue shift with an increase in the injection current density because of the indium-localization-induced band-filling effect. , …”

“…In particular, InGaN-based light-emitting diodes (LEDs) are desirable for light sources in displays and lighting systems with a variety of visible-light colors ranging from blue to green emission, except for red emission because of severe material degradation and a strong quantum-confinement Stark effect. − Therefore, to realize a full-color LED display, AlGaAs- or AlGaInP-based red LEDs must be combined with InGaN-based blue and green LEDs. − In addition, in the next-generation micro-LED display, the integration of high-transfer technologies between the LED wafers and the display panel is highly challenging work in reducing manufacturing cost and improving display reliability. , Therefore, instead of the complex process of transferring two or more light sources, the monolithic red (R), green (G), and blue (B) InGaN-based LEDs capable of achieving three RGB color emissions on one wafer have been studied by using various quantum-well structures and nanostructure- (e.g., nanofacets, nanocolumns, and nanodisks). ,− Among monolithic RGB LED technologies for micro-LED display light sources, semipolar InGaN-based LEDs are attracting much attention because they can emit full-color emissions from red to blue using strong indium localization. − In general, because the indium incorporation rate of a semipolar (11–22) GaN film is higher than that of nonpolar GaN films, the semipolar (11–22) GaN is useful for achieving longer-wavelength (>500 nm) LEDs . The incorporation of indium in semipolar GaN films has been demonstrated to be influenced by the crystallographic planes of their arrowhead-like surface structure. − The arrowhead-like surface structure of the semipolar (11–22) GaN film has a few crystal planes, such as (20–21), (10–11), and (11–22), that can exhibit different indium compositions . This means that the emission energy of the InGaN active layer can be different in the arrowhead-like surface structure.…”

“…This means that the emission energy of the InGaN active layer can be different in the arrowhead-like surface structure. This diverse and high indium incorporation rate makes it suitable for forming multiwavelength emissions using semipolar (11–22) GaN-based LEDs. , To take advantage of the strong band-filling effect, the size of an LED is an important measure of its injection current density, which indicates that, as the injection current increases, the emission spectrum of the LED shows a blue shift. , When the same injection current is applied to micro-LEDs with different sizes, the micro-LED with the smaller area emits at a shorter wavelength because of the band-filling effect. In addition, smaller micro-LEDs can achieve higher efficiencies at higher injection current densities because of the improved current spreading effect …”