Experimental investigations on growth of GaN-based materials for light emitting applications

Thumbnail Image

Files

isbn9789526048468.pdf (6.53 MB)

URL

Journal Title

Journal ISSN

Volume Title

School of Engineering | Doctoral thesis (article-based) | Defence date: 2012-11-16
Checking the digitized thesis and permission for publishing
Instructions for the author
Unless otherwise stated, all rights belong to the author. You may download, display and print this publication for Your own personal use. Commercial use is prohibited.

Authors

Date

2012

Department

Mikro- ja nanotekniikan laitos
Department of Micro- and Nanosciences

Major/Subject

Mcode

Degree programme

Language

en

Pages

93 + app. 48

Series

Aalto University publication series DOCTORAL DISSERTATIONS, 143/2012

Abstract

This work investigates the fabrication, characterization and application of GaN-based layers in light emitting structures. All the thin films and light emitting diodes (LEDs) discussed in this thesis were grown by metal organic vapor phase epitaxy (MOVPE). The objective of this thesis was to improve the material quality and light extraction of III-N optoelectronic structures. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), photoluminescence (PL) and electroluminescence (EL) were used to characterize the samples. GaN layers were grown on GaN templates having hexagon shaped openings. Embedded voids were created at the GaN-sapphire interface with a novel process described in this work. A control over the shape of the voids was demonstrated. It was observed that changing the diameter of the hexagonal openings has an impact on the inclination angle of the sidewalls of embedded voids. The GaN layers having the embedded voids with low inclination angle sidewalls showed an improved material quality. Significant threading dislocation (TD) bending was observed near such voids. InGaN/GaN LEDs were grown on GaN layers with embedded voids of different shapes. Improved material quality and more efficient light extraction due to the introduced void geometry enhanced the light output of 60 degrees inclined sidewall embedded void LEDs. Light extraction enhancement was also studied by mask-less chemical roughening of the back side of the sapphire substrate. An optimized roughening process improved the light extraction from the LED structure by more than 20 %. The compositional dependence of indium and aluminum on MOVPE growth conditions in quaternary InAlGaN layers was investigated. InGaN multi-quantum well structures (MQWs) having quaternary barriers with near-UV emission were also studied. It was observed that the internal quantum efficiency (IQE) of InGaN/InAlGaN MQW structure was sensitive to the barrier layer composition. A proof-of-concept LED based augmented reality application was demonstrated. A working InGaN/GaN single micro-pixel light source was integrated into a contact lens. The LED micropixel display was controlled via a radio frequency transmitter in free space and tested on a rabbit.

Description

Supervising professor

Sopanen, Markku, Dr., Aalto University, Finland

Thesis advisor

Suihkonen, Sami, Dr., Aalto University, Finland

Keywords

LED, III-nitrides, MOVPE, light extraction, augmented reality

Other note

Parts

  • [Publication 1]: M. Ali, A.E. Romanov, S. Suihkonen, O. Svensk, P.T. Torma, M. Sopanen, H. Lipsanen, M.A. Odnoblyudov and V.E. Bougrov. Void shape control in GaN re-grown on hexagonally patterned mask-less GaN. Journal of Crystal Growth, 315, 188 (2011).
  • [Publication 2]: M. Ali, A.E. Romanov, S. Suihkonen, O. Svensk, S. Sintonen, M. Sopanen, H. Lipsanen, V.N. Nevedomsky, N.A. Bert, M.A. Odnoblyudov and V.E. Bougrov. Analysis of threading dislocations in void shape controlled GaN re-grown on hexagonally patterned mask-less GaN. Journal of Crystal Growth, 344, 59 (2012).
  • [Publication 3]: M. Ali, O. Svensk, L. Riuttanen, M. Kruse, S. Suihkonen, A.E. Romanov, P.T. Torma, M. Sopanen, H. Lipsanen, M.A. Odnoblyudov and V.E. Bougrov. Enhancement of near-UV GaN LED light extraction efficiency by GaN/sapphire template patterning. Semiconductor Science and Technology, 27, 082002 (2012).
  • [Publication 4]: P.T. Torma, O. Svensk, M. Ali, S. Suihkonen, M. Sopanen, M.A. Odnoblyudov and V.E. Bougrov. Maskless roughening of sapphire substrates for enhanced light extraction of nitride based blue LEDs. Solid-State Electronics, 53, 166 (2009).
  • [Publication 5]: S. Suihkonen, O. Svensk, P.T. Torma, M. Ali, M. Sopanen, H. Lipsanen, M.A. Odnoblyudov and V.E. Bougrov. MOVPE growth and characterization of InAlGaN films and InGaN/InAlGaN MQW structures. Journal of Crystal Growth, 310, 1777 (2008).
  • [Publication 6]: M. Ali, S. Suihkonen, O. Svensk, P. T. Torma, M. Sopanen, H. Lipsanen, M.A. Odnoblyudov and V.E. Bougrov. Study of composition control and capping of MOVPE grown InGaN/InxAlyGa1−x−yN MQW Structures. Physica Status Solidi (c), 5 , 3020 (2008).
  • [Publication 7]: A.R. Lingley, M. Ali, Y. Liao, R. Mirjalili, M. Klonner, M. Sopanen, S. Suihkonen, T. Shen, B.P. Otis, H. Lipsanen and B.A. Parviz. A single pixel wireless contact lens display. Journal of Micromechanics and Microengineering, 21, 125014 (2011).

Citation

Permanent link to this item

https://urn.fi/URN:ISBN:978-952-60-4846-8

Collections

[diss] Insinööritieteiden korkeakoulu / ENG