Photon management of GaN-based optoelectronic devices via nanoscaled phenomena

Abstract

Photon management is essential in improving the performances of optoelectronic devices including light emitting diodes, solar cells and photo detectors. Beyond the advances in material growth and device structure design, photon management via nanoscaled phenomena have also been demonstrated as a promising way for further modifying/improving the device performance. The accomplishments achieved by photon management via nanoscaled phenomena include strain-induced polarization field management, crystal quality improvement, light extraction/harvesting enhancement, radiation pattern control, and spectrum management. In this review, we summarize recent development, challenges and underlying physics of photon management in GaN-based light emitting diodes and solar cells.

Introduction

III-nitride materials have attracted great attention over the past decades. The bandgaps of the III-nitrides including AlN, GaN, InN materials and their related binary, ternary and quaternary compounds span 0.7 to 6.2 eV, which contribute to the emission/absorption ranging from deep ultraviolet (UV) to near infrared (NIR) region. Such large bandgap tunability, high thermal stability, direct bandgap make III-N materials the promising candidate for optoelectronic devices, such as light emitting diodes (LEDs), laser diodes (LDs) and solar cells [1], [2], [3]. Various applications such as full color displays, high density optical storage, automobile lights, visible light communication (VLC), biotechnology, and photovoltaic devices are vigorously developed.

However, the GaN-based devices are still obstructed by several issues, including low light extraction/harvesting, high defect density and strain-induced polarization [4], [5], [6], [7], [8]. To address these issues, there have been numerous approaches proposed over the past years. Fig. 1 shows the timeline of technology progresses in GaN optoelectronic devices. At early stages, the main efforts were focused on improving material qualities [9], [10] and device structuring [11], [12], [13]. As time passes, the advanced growth/fabrication techniques enable photon management in nanostructured interfaces, further enhancing the quantum efficiencies of devices. For the materials in low-dimension scale, many distinctive phenomena, e.g. reflection suppressing, scattering increase, strain reduction, can be observed in the optoelectronic devices with superior performances [14], [15], [16], [17], [18]. In the following sections, the photon management via nanoscaled phenomena in GaN-based LEDs and solar cells will be reviewed and discussed in details.