Laser Lift-Off 공정과 SiO2/ZrO2 기반 분포 브래그 반사막을 이용한 3족 질화물 계열 공명공진기 발광다이오드의 제작과 측정

Abstract

ABSTRACT

Fabrication and Measurements of Ⅲ-Nitride based Resonant Cavity Light-Emitting Diodes using Laser Lift-Off process and SiO2/ZrO2 Distributed Bragg Reflector

Jae-Hoon Kim Advisor : Prof. Hyun-Su Kim, Ph.D. Department of Photonic Engineering, Graduate School of Chosun University

Resonant cavity light emitting diodes (RC-LEDs) have many merits such as circular output beam shape, narrow output line-width and forward directed light output. So RC-LEDs have lots of applications in the area which needs high-speed modulation or high coupling efficiency. This research deals with fabrications and measurements of Ⅲ-Nitride based RC-LEDs using laser lift-off (LLO) process and SiO2/ZrO2 distributed bragg reflectors (DBRs). Two different cavities structures of RC-LEDs were fabricated. One was using metal reflectors and SiO2-ZrO2 DBR for both side mirrors of cavity and the other using SiO2-ZrO2/SiO2-ZrO2 DBR. The epitaxial layers were grown on sapphire substrate by organic-metallic vapor phase epitaxy (OMVPE). After 0.5-㎛-thick undoped GaN layer and a 2.0-㎛-thick n-type GaN layer were grown, a multiple quantum wells (MQWs) of five periods of a 2-㎚-thick InGaN well and an 7-㎚-thick GaN barrier were grown. The target emission wavelength of MQWs was 460 ㎚. Then a 90-㎚-thick p-type GaN layer was grown. Thin film of indium tin oxide (ITO) was deposited on the epitaxial layer for current spreading and the Ni/Ag/Pt metal reflectors or SiO2/ZrO2 DBR layers were deposited on top. DBR Structure was deposited using physical vapor deposition system. Because of SiO2-ZrO2 DBR is insulators, we made several hole patterns at SiO2-ZrO2 DBR for current injection. We used inductively coupled plasma (ICP) for this holes pattern process. The thick bonding metal (Ti/Au/Sn/Au) was deposited over the entire sample. Then the sample was bonded onto a highly conductive Au-coated Si substrate under high temperature and pressure. To remove the sapphire substrate, LLO technique was employed. After sapphire substrate removal, the GaN surface was treated with a HCl solution to remove the residual Ga material. After LLO process, a Cl2-based ICP was used for etching the n-GaN layer in order to do the formation of GaN cavity with the resonant cavity length. The mesa etch was performed to separate each device on wafer. The sample sizes are about 1000 × 1000 ㎛2. A patterned Cr-Au electrode was deposited on n-GaN as the n-type contact layer. Finally, SiO2/ZrO2 DBR layers were deposited on n-GaN and DBRs were etched with smaller size than n-electrode size by Cl2-based ICP. The fabricated GaN-based blue RC-LEDs were measured for the electrical and optical charaterization. The device were performed with multi modes operation of mode spacing Δλ=18 ㎚ and with FWHM 12 ㎚. The device was well working up to 0∼500 ㎃ input current level. The output luminous intensity is 350 m㏅ at 460 ㎚ peak wavelength under 350 ㎃ input current. From the measurements of the reflectance of RC-LED structure, we verified that the reflectance of cavity structure corresponds with output spectrum of RC-LED.