Temperature dependent characteristics of GaN/GaInN based light emitting diodes

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.