Author
Meyaard, David S.
Other Contributors
Schubert, E. Fred; Bhat, Ishwara B.; Huang, Zhaoran Rena; Wetzel, Christian;
Date Issued
2013-08
Subject
Electrical engineering
Degree
PhD;
Terms of Use
This electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author.;
Abstract
The Shockley-Read-Hall recombination rate increases with temperature and is found to greatly reduce the light output at low current densities (≪ 35 A/cm2). However, this mechanism fails to explain the drop in light-output power at high current densities (≫ 35 A/cm2). At the typical operating current density (≈ 35 A/cm2), as temperature increases, we find that Shockley-Read-Hall recombination is not sufficient to fully explain the reduction in efficiency. Electron leakage out of the active region is shown to be a major contribution to the recombination at 450 K and 35 A/cm2. Both Shockley-Read-Hall and electron leakage significantly contribute to the reduction in light-output power in GaInN/GaN light-emitting diodes at high temperatures.; Methods of reducing these two recombination mechanisms are discussed to improve the temperature stability in GaInN/GaN based light-emitting diodes. Firstly, reducing the threading dislocation density (TDD) by using lattice matched substrates, or unique buffer layers, would greatly reduce the Shockley-Read-Hall recombination. Secondly, electron leakage must be reduced. This can be completed by: (i) enhancing p-type doping, leading to less asymmetry of carrier concentration or mobility in the junction, (ii) reducing the strain in the epitaxial layers with polarization matched material, or applying external strain via a capping layer, and (iii) redesigning the active region of the LED to have more quantum wells, thereby hindering electron leakage.; The light-output power emitted by GaN-based light-emitting diodes decreases with increasing temperature; this is a well-known phenomenon with significant impact in the field of solid-state lighting. In this work, the different mechanisms causing this reduction in light-output power are discussed and analyzed. Two important loss mechanisms and their temperature dependence are discussed: Shockley-Read-Hall recombination and electron leakage out of the active region. Each of these is examined in detail, and the dominance of each mechanism's role in the reduction in efficiency is studied at different current densities. The temperature dependence of these mechanisms is quantitatively extracted from experimental data.;
Description
August 2013; School of Engineering
Department
Dept. of Electrical, Computer, and Systems Engineering;
Publisher
Rensselaer Polytechnic Institute, Troy, NY
Relationships
Rensselaer Theses and Dissertations Online Collection;
Access
Restricted to current Rensselaer faculty, staff and students. Access inquiries may be directed to the Rensselaer Libraries.;