Improved light extraction efficiency of GaN-based flip-chip light-emitting diodes with an antireflective interface layer

Abstract

GaN-based flip-chip light-emitting diodes (FC-LEDs) grown on nanopatterned sapphire substrates (NPSS) are fabricated using self-assembled SiO2 nanospheres as masks during inductively coupled plasma etching. By controlling the pattern spacing, epitaxial GaN can be grown from the top or bottom of patterns to obtain two different GaN/substrate interfaces. The optoelectronic characteristics of FC-LED chips with different GaN/sapphire interfaces are studied. The FC-LED with an antireflective interface layer consisting of a NPSS with GaN in the pattern spacings demonstrates better optical properties than the FC-LED with an interface embedded with air voids. Our study indicates that the two types of FC-LEDs grown on NPSS show higher crystal quality and improved electrical and optical characteristics compared with those of FC-LEDs grown on conventional planar sapphire substrates.

Light Extraction Efficiency of GaN-Based Micro-Scale Light-Emitting Diodes Investigated Using Finite-Difference Time-Domain Simulation

“…Because the interference pattern of the light emitted from the QWs with the light reflected at the Ag reflector depends on the relative distance between the QWs and Ag, the emission profile, and hence the LEE, can be dependent on t p . This light interference effect in vertical or flip-chip structures has also been reported in previous works [16]- [18], [40]. The dependence of the LEE on t p was also investigated for other L values.…”

“…Nevertheless, the 3-D FDTD method can be employed for the LEE simulation of a vertical chip or thin-film flip-chip structure where the substrate is removed. In this case, the lateral dimension of an LED structure is truncated by imposing metal boundary conditions, assuming that light is mostly emitted through the top surface of the LED chip and the sidewall emission is negligible [16]- [18]. This assumption can be valid because the lateral dimension of a large-area vertical LED chip can be as large as 1 mm whereas the vertical dimension is only several μms.…”

Developments for enhancing the luminous intensity of LEDs by optimizing their structures

“…Furthermore, the encapsulation advantage of this structure will enable it to work under multiple conditions. During the encapsulation, the electrodes are able to contact with the silicon submount, which is a good thermal conductor so the heat can be dissipated quickly to protect the material from being more intrinsic and therefore enhance the performance of LED [25]. Hence, the FC-LED is able to be used for high power purpose with fewer limitations.…”