2Material Science and Technology of Japan, 54㸦2017㸧112㹼117Aug. 2017

Regular Paper
The Formation of Air Void on Patterned Sapphire Substrate by
Selective Photoresist Carbonization
Junsung PARK1, Dae-sik KIM1, Woo Seop JEONG1, Seung Hee CHO1, Chul KIM1,Hyun-a KO1, Doowon LEE1 and Dongjin BYUN1,*1

Department of Materials Science and Engineering, Korea University, Seoul 02841, Korea

Received Jun. 10, 2017; accepted for publication Jul. 17, 2017
ABSTRACTIn this study, to improve the light extraction efficiency of light emitting diodes, we investigated new methods thatform an air void on patterned sapphire substrate (PSS) without wet etching process. It was confirmed GaN wasgrown on specific planes such as n-like plane, c-plane in PSS by behavior of GaN growth on PSS as time changes.
Air void can be built up by suppressing c-plane and growing on n-like plane in PSS lens, using selective photoresist
mask. To analyze the cause of selective growth on PSS, the contact angle measurement was implemented and thecause of growth suppression can be found by the surface energy from contact angle.
Keywords: gallium nitride, patterned sapphire substrate, metal-organic chemical vapor deposition

1.

Introduction

multi-step method [12] have been implemented. Several methods

Gallium nitride (GaN)-based light emitting diodes (LEDs) haveincluding use of patterned sapphire substrate (PSS) [13-16],

attracted much attention in solid-state lighting such as full color

embedded air void [17,18], patterning of transparent conductiveor white LED displays and backlights for liquid crystal displays.

oxide layer [19], and sidewall etching of GaN [20,21] have been

Although GaN-based LEDs are commercially available, there isalso developed to improve the LEE of LED. Among theseroom for improvement of external quantum efficiency (EQE).

technologies for EQE, the PSSs method is recently being used inThe EQE of LEDs is primarily linked with internal quantum

manufacturing industries because of the enhancement of IQE andefficiency (IQE) and light extraction efficiency (LEE). The low

LEE by decreasing TD and improving photon scattering.

IQE is attributed to the low crystal quality of GaN epitaxial layer

However, air void structure in LEDs has been also studied as[1] which affected by the threading dislocation density (TD) bymeans to increase IQE and LEE for high efficiency

the large lattice mismatch of lattice constant and thermal

optoelectronic devices [22-24]. Although most of LEDs with air

expansion coefficient between the GaN epitaxial layer andvoid have been made using an additional crystallographic wet

sapphire substrate [2-4]. Another major issue for low EQE is low

etching process [22-24], excessive wet etching process can result

LEE, which primarily results from total internal reflection ofin epitaxial growth problem including surface pits and a roughlight caused by the difference in refractive indexes of GaN andsurface [25].

the sapphire substrate. Because of total internal reflection, mostTo overcome issues by wet etching process, a new method toof the photons generated from multi-quantum well (MQW)

build up air void by the growth of GaN on lens ridge of PSS wascannot escape from GaN. Therefore, improvement of IQE andproposed without a wet etching process. But it is not easy toLEE is a major issue for high performance LED.

control the behavior of GaN growth on various planes existed onPSS.

Many useful growth techniques have been proposed toenhance the EQE of GaN-based LED. To improve crystal quality

In this study, we investigate the behavior of GaN growth onforlateral

PSS and introduce a method to fabricate air void by the control

overgrowth(ELOG) [5-7], pendeo-epitaxy(PE)[8], AlN bufferof the surface energy on PSS lens, using selective photoresist

layer[9], facet-controlled epitaxial lateral overgrowth [10,11] andcarbonization.

IQE,variousconcepts

suchasepitaxial*Corresponding author: dbyun@korea.ac.kr(112)