Since the AlGaInN alloy has a continuous direct bandgap from about 0.7 eV
(InN) to 6.2 eV (AlN), nitride-based materials can cover most of the electromag netic spectrum from near-infrared to ultraviolet. Based on this feature, nitride based light-emitting diode (LED) devices have been widely used. With the first
commercialization of blue LED devices in 1993, the LED industry became more
and more important in the field of lighting. As a typical light-emitting material,
LED devices are not only determined by their own components, but also their
luminous efficiency is one of the focuses of attention. Generally speaking, the
standard for measuring the luminous efficiency of LED devices is the ratio of the
number of injected carriers to the number of emitted photons, that is, the external
quantum efficiency (EQE). In order to obtain a higher EQE, it can be improved
from three aspects, namely internal quantum efficiency (IQE), light extraction ef ficiency (LEE) and injection efficiency (IE). However, since LED devices are often
grown by vapor phase epitaxy, the epitaxial growth substrate often absorbs the
light emitted by the LED device, thereby reducing the EQE of the entire device
and affecting the luminous efficiency. Especially as the light-emitting wavelength
of LEDs becomes longer and longer, the EQE of LED devices tends to drop from
more than 80% to 4% or even lower (the decline of red LEDs will be more signif icant). At the same time, as the size of LED devices decreases, the proportion of
damage caused by the mesa etching process and the surface recombination area
of devices (such as Micro LED devices) increases accordingly, and EQE will also
show a clear downward trend. Therefore, in addition to further improving EQE
through internal quantum efficiency, increasing LEE as much as possible through
structural changes is also a key point to improve EQE. In our study, based on
our group’s own grown red LEDs, we successfully transferred structured vertical
InGaN red LEDs from Si(111) substrates to new substrates, achieving further
improvements in LEE. At the same time, it also provides options for applying
this technology to LED devices and micro-LED devices of various wavelengths in
the future. The LED device with the vertical structure has a low turn-on work ing voltage and a small series resistance. The whole process adopts dry etching
technology, which makes the process more precise and reliable. Compared to
standard LED devices, the operating voltage and series resistance of LEDs are
changed from 30Ω to less than 10Ω respectively, and the LEE is improved by 70%,
which is mainly attributed to the removal of the light-collecting substrate and the
use of metal reflective layers to improve light extraction efficiency. Furthermore,
although the process is an improvement over LEE, this structure-based process
improvement can be used for LEDs of various wavelengths as well as micro-LEDs
in the future. This typical substrate transfer technique can transfer very thin
(3 micron) LED structures from one substrate to another without damaging the
device itself, thus providing a way to realize flexible substrates in the near future.
| Identifer | oai:union.ndltd.org:kaust.edu.sa/oai:repository.kaust.edu.sa:10754/691790 |
| Date | 03 May 2023 |
| Creators | Jin, Yu |
| Contributors | Ohkawa, Kazuhiro, Computer, Electrical and Mathematical Science and Engineering (CEMSE) Division, Elatab, Nazek, Han, Yu |
| Source Sets | King Abdullah University of Science and Technology |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | 2024-05-18, At the time of archiving, the student author of this thesis opted to temporarily restrict access to it. The full text of this thesis will become available to the public after the expiration of the embargo on 2024-05-18. |
| Relation | N/A |
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