Abstract/Details

Improvement of III-nitride visible and ultraviolet light-emitting diode performance, including extraction efficiency, electrical efficiency, thermal management and efficiency maintenance at high current densities


2009 2009

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Abstract (summary)

In this work, highly efficient broad-area LEDs on bulk GaN substrates were developed and the fabrication process and device layout were optimized. This optimization relied in part on electrical, optical, thermal and recombination models. The peak external quantum efficiency of the 450 nm LEDs was over 68% when biased at 20 mA. The efficiency characteristic showed a typical droop curve, decreasing at high current densities. The cause of this droop is unknown. An exploratory experiment was conducted to characterize electron overflow and its role in efficiency droop. Novel device structures were developed, allowing direct measurement of overflow electrons in LED-like structures under electrical injection. In these test structures, electrons were observed in the p-type region of the LED only at current densities where efficiency droop was active. The onset of efficiency droop was preceded by the onset of electron overflow. However, the magnitude of the overflow current could not be measured and it is undetermined whether the dominant cause of efficiency droop is electron overflow or some other process such as Auger recombination. Calibration structures allowing measurement of the magnitude of the overflow are proposed.

Work on deep-ultraviolet, 275 nm, LEDs is also presented. Demonstration of direct-wafer bonded LEDs to β-Ga2O3 is presented. A SiC substrate removal process is discussed. LEDs fabricated by this flip-chip process exhibited up to 1.8 times greater power compared to LEDs fabricated by a standard process but suffered from increased forward voltage and premature failure. Further process development leading to electrically efficient operation is proposed.

Indexing (details)


Subject
Electrical engineering;
Materials science
Classification
0544: Electrical engineering
0794: Materials science
Identifier / keyword
Applied sciences; Current density; Droop; Electrical efficiency; Extraction efficiency; Gallium nitride; Light-emitting diodes; Nitride; Thermal management; Ultraviolet
Title
Improvement of III-nitride visible and ultraviolet light-emitting diode performance, including extraction efficiency, electrical efficiency, thermal management and efficiency maintenance at high current densities
Author
Vampola, Kenneth
Number of pages
444
Publication year
2009
Degree date
2009
School code
0035
Source
DAI-B 70/11, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
9781109483697
Advisor
DenBaars, Steven P.; Nakamura, Shuji
Committee member
Hu, Evelyn; Mishra, Umesh; Speck, James S.
University/institution
University of California, Santa Barbara
Department
Materials
University location
United States -- California
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
3379526
ProQuest document ID
304852210
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/304852210
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