passivation of InGaN/GaN nanopillar light emitting diodes

Open Access
Author:
Choi, Won Hyuck
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 03, 2013
Committee Members:
  • Suzanne E Mohney, Thesis Advisor
  • Jian Xu, Thesis Advisor
  • Joan Marie Redwing, Thesis Advisor
Keywords:
  • nanopillar
  • light emitting diode
  • passivation
  • InGaN/GaN
Abstract:
Recently, InGaN/GaN based blue light emitting diodes (LEDs) have become widely available commercially, but their efficiency is reduced due to the quantum confined Stark effect (QCSE) induced by the InGaN/GaN mismatch. These LEDs, when combined with a phosphor or other LEDs, can be used to provide white lighting, and maximizing their energy efficiency is desirable. Therefore, a new LED structure using nanopillars has been studied, which increases the surface area for light to escape as well as reducing the quantum confined Stark effect in order to improve the device efficiency. However, when InGaN/GaN nanopillars are prepared by dry etching, N vacancies and group Ⅲ oxides are created on the nanopillar sidewalls, causing excessive leakage current and non-radiative surface recombination. As a result, the internal quantum efficiency drops, and it degrades the device efficiency. In this research, reducing the etch rate and adding consecutive KOH wet etching and (NH4)2S/ isopropanol passivation steps were studied to reduce the sidewall damage and increase the device efficiency. The photoluminescence intensity in nanopillars prepared with the slow etch rate (0.18 nm/s) was 2 times higher than that of planar structures. In nanopillar LEDs, an additional 4 times higher electroluminescence intensity and suppressed leakage current under reverse and forward bias were recorded with sulfur passivation.