Enhanced performance of GaN-based visible flip-chip mini-LEDs with highly reflective full-angle distributed Bragg reflectors

Abstract

High-efficiency GaN-based visible flip-chip miniaturized-light emitting diodes (FC mini-LEDs) are desirable for developing white LED-backlit liquid crystal displays. Here, we propose a full-angle Ti3O5/SiO2 distributed Bragg reflector (DBR) for blue and green FC mini-LEDs to enhance the device performance. The proposed full-angle Ti3O5/SiO2 DBR is composed of different single-DBR stacks optimized for central wavelength in blue, green, and red light wavelength regions, resulting in wider reflective bandwidth and less angular dependence. Furthermore, we demonstrate two types of GaN-based FC mini-LEDs with indium-tin oxide (ITO)/DBR and Ag/TiW p-type ohmic contacts. Experimental results exhibit that the reflectivity of full-angle DBR is higher than that of Ag/TiW in the light wavelength range of 420 to 580 nm as the incident angle of light increases from 0° to 60°. As a result, the light output powers (LOPs) of blue and green FC mini-LEDs with ITO/DBR are enhanced by 7.7% and 7.3% in comparison to blue and green FC mini-LEDs with Ag/TiW under an injection current of 10 mA. In addition, compared with FC mini-LED with Ag/TiW, light intensity of FC mini-LED with ITO/DBR is improved in side direction, which is beneficial to mix light in backlight system of liquid crystal displays (LCDs).

Strategically constructed high-reflectivity multiple-stack distributed Bragg reflectors for efficient GaN-based flip-chip mini-LEDs

“…Furthermore, based on design principle of full-angle DBRs [21], we develop a 30-layer full-angle DBR consisting of 15 sub-DBRs; each sub-DBR is simply constructed as an array of two alternating nanometer-thick layers of Ti 3 O 5 and SiO 2 . Layer parameters of each sub-stack of quintuple-stack DBR and full-angle DBR are shown in tables 1 and 2, respectively.…”

“…We fabricated blue FC mini-LED with ITO/quintuple-stack DBR (denoted as sample A) and blue FC mini-LED with ITO/full-angle DBR (denoted as sample B). The detailed epitaxial structure of sample A and sample B can be found in previous work [21]. The peak wavelength of sample A and sample B was 465 nm.…”

“…Various reflectors, such as metallic reflectors [12,17,18], distributed Bragg reflectors (DBRs) [19][20][21][22], omnidirectional reflectors [23,24], and hybrid reflectors [25], have been proposed to attain high light extraction efficiency (LEE) and to further boost external quantum efficiency of FC LEDs. Owing to high reflectivity, metallic reflectors and DBRs are widely applied in FC mini-LEDs.…”

“…These methods would be beneficial for optimization design of conventional DBRs. Recently, full-angle DBRs have been proposed to suppress angular dependence by broadening their reflective bandwidth [21]. The full-angle DBRs are made of numerous sub-DBRs, which is constructed as a pair of alternating Ti 3 O 5 /SiO 2 dielectric layers.…”

Recent Progress in Long‐Wavelength InGaN Light‐Emitting Diodes from the Perspective of Epitaxial Structure

“…Thus, further improvement is required for InGaN LEDs in long‐wavelength region. Of course, challenges universally encountered by LED devices, such as efficiency droop, [ 22 ] carrier injection, [ 23 ] and light extraction, [ 24 ] are also present in long‐wavelength InGaN LEDs. In this review, we will discuss the recent progress made in InGaN long‐wavelength LEDs from the perspective of epitaxial structure, together with the important techniques to enhance the device performance.…”