Advanced

Elimination of resistive losses in large-area LEDs by new diffusion-driven devices

Kivisaari, Pyry LU ; Kim, Iurii; Suihkonen, Sami and Oksanen, Jani (2017) Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XXI 2017 In Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XXI 10124.
Abstract

High-power operation of conventional GaN-based light-emitting diodes (LEDs) is severely limited by current crowding, which increases the bias voltage of the LED, concentrates light emission close to the p-type contact edge, and aggravates the efficiency droop. Fabricating LEDs on thick n-GaN substrates alleviates current crowding but requires the use of expensive bulk GaN substrates and fairly large n-contacts, which take away a large part of the active region (AR). In this work, we demonstrate through comparative simulations how the recently introduced diffusion-driven charge transport (DDCT) concept can be used to realize lateral heterojunction (LHJ) structures, which eliminate most of the lateral current crowding. Specifically in... (More)

High-power operation of conventional GaN-based light-emitting diodes (LEDs) is severely limited by current crowding, which increases the bias voltage of the LED, concentrates light emission close to the p-type contact edge, and aggravates the efficiency droop. Fabricating LEDs on thick n-GaN substrates alleviates current crowding but requires the use of expensive bulk GaN substrates and fairly large n-contacts, which take away a large part of the active region (AR). In this work, we demonstrate through comparative simulations how the recently introduced diffusion-driven charge transport (DDCT) concept can be used to realize lateral heterojunction (LHJ) structures, which eliminate most of the lateral current crowding. Specifically in this work, we analyze how using a single-side graded AR can both facilitate electron and hole diffusion in DDCT and increase the effective AR thickness. Our simulations show that the increased effective AR thickness allows a substantial reduction in the efficiency droop at large currents, and that unlike conventional 2D LEDs, the LHJ structure shows practically no added efficiency loss or differential resistance due to current crowding. Furthermore, as both electrons and holes enter the AR from the same side without any notable potential barriers in the LHJ structure, the LHJ structure shows an additional wall-plug efficiency gain over the conventional structures under comparison. This injection from the same side is expected to be even more interesting in multiple quantum well structures, where carriers typically need to surpass several potential barriers in conventional LEDs before recombining. In addition to simulations, we also demonstrate selective-area growth of a finger structure suitable for operation as an LHJ device with 2μm distance between n- and p-GaN regions.

(Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Chapter in Book/Report/Conference proceeding
publication status
published
subject
keywords
composition grading, current crowding, diffusion-driven charge transport, high-power operation, Light-emitting diodes, selective-area growth
in
Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XXI
volume
10124
publisher
SPIE
conference name
Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XXI 2017
external identifiers
  • scopus:85020237759
DOI
10.1117/12.2251108
language
English
LU publication?
yes
id
c3257f3b-3b51-449a-94e9-dddbae8c3b76
date added to LUP
2017-06-30 11:48:19
date last changed
2017-06-30 11:48:19
@inproceedings{c3257f3b-3b51-449a-94e9-dddbae8c3b76,
  abstract     = {<p>High-power operation of conventional GaN-based light-emitting diodes (LEDs) is severely limited by current crowding, which increases the bias voltage of the LED, concentrates light emission close to the p-type contact edge, and aggravates the efficiency droop. Fabricating LEDs on thick n-GaN substrates alleviates current crowding but requires the use of expensive bulk GaN substrates and fairly large n-contacts, which take away a large part of the active region (AR). In this work, we demonstrate through comparative simulations how the recently introduced diffusion-driven charge transport (DDCT) concept can be used to realize lateral heterojunction (LHJ) structures, which eliminate most of the lateral current crowding. Specifically in this work, we analyze how using a single-side graded AR can both facilitate electron and hole diffusion in DDCT and increase the effective AR thickness. Our simulations show that the increased effective AR thickness allows a substantial reduction in the efficiency droop at large currents, and that unlike conventional 2D LEDs, the LHJ structure shows practically no added efficiency loss or differential resistance due to current crowding. Furthermore, as both electrons and holes enter the AR from the same side without any notable potential barriers in the LHJ structure, the LHJ structure shows an additional wall-plug efficiency gain over the conventional structures under comparison. This injection from the same side is expected to be even more interesting in multiple quantum well structures, where carriers typically need to surpass several potential barriers in conventional LEDs before recombining. In addition to simulations, we also demonstrate selective-area growth of a finger structure suitable for operation as an LHJ device with 2μm distance between n- and p-GaN regions.</p>},
  author       = {Kivisaari, Pyry and Kim, Iurii and Suihkonen, Sami and Oksanen, Jani},
  booktitle    = {Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XXI},
  keyword      = {composition grading,current crowding,diffusion-driven charge transport,high-power operation,Light-emitting diodes,selective-area growth},
  language     = {eng},
  publisher    = {SPIE},
  title        = {Elimination of resistive losses in large-area LEDs by new diffusion-driven devices},
  url          = {http://dx.doi.org/10.1117/12.2251108},
  volume       = {10124},
  year         = {2017},
}