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

Pyry Kivisaari*, Iurii Kim, Sami Suihkonen, Jani Oksanen

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

3 Citations (Scopus)
7 Downloads (Pure)

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 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.

Original languageEnglish
Title of host publicationLight-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XXI
EditorsJK Kim, MR Krames, LW Tu, M Strassburg
PublisherSPIE - The International Society for Optical Engineering
ISBN (Electronic)9781510606890
DOIs
Publication statusPublished - 2017
MoE publication typeA4 Article in a conference publication
EventSPIE Conference on Light-Emitting Diodes - San Francisco, United States
Duration: 30 Jan 20171 Feb 2017
Conference number: 21

Publication series

NameProceedings of SPIE : the International Society for Optical Engineering
Volume10124
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X

Conference

ConferenceSPIE Conference on Light-Emitting Diodes
CountryUnited States
CitySan Francisco
Period30/01/201701/02/2017

Keywords

  • composition grading
  • current crowding
  • diffusion-driven charge transport
  • high-power operation
  • Light-emitting diodes
  • selective-area growth

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