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On the Light Emission in GaN Based Heterostructures at High Injection

Published online by Cambridge University Press:  31 January 2011

Xianfeng Ni ,
Xing Li ,
Huiyong Liu ,
Natalia Izyumskaya ,
Vitaliy Avrutin ,
Ümit Özgür ,
Hadis Morkoç ,
Tanya Paskova ,
Greg Mullholland  and
Keith R. Evans
Xianfeng Ni
Affiliation:
nix@vcu.edu, Virginia Commonwealth University, Electrical and Computer Engineering, 23284, Virginia, United States
Xing Li
Affiliation:
lix9@vcu.edu, Virginia Commonwealth University, Electrical and Computer Engineering, Richmond, Virginia, United States
Huiyong Liu
Affiliation:
liuh3@vcu.edu, Virginia Commonwealth University, Electrical and Computer Engineering, 23284, Virginia, United States
Natalia Izyumskaya
Affiliation:
nizioumskaia@vcu.edu, Virginia Commonwealth University, Electrical and Computer Engineering, 23284, Virginia, United States
Vitaliy Avrutin
Affiliation:
vavrutin@vcu.eduv.avrutin@mail.ru, Virginia Commonwealth University, Electrical and Computer Engineering, 601 West Main St., Richmond, Virginia, 23284, United States, 1 (804)827 7000 ext 357, 1 (804)828 4269
Ümit Özgür
Affiliation:
uozgur@vcu.edu, Virginia Commonwealth University, Electrical and Computer Engineering, 23284, Virginia, United States
Hadis Morkoç
Affiliation:
hmorkoc@vcu.eduhmorkoc@vcu.edu, Virginia Commonwealth University, Electrical and Computer Engineering, R, Virginia, United States
Tanya Paskova
Affiliation:
paskova@kymatech.com, Kyma Tech, Raleigh, North Carolina, United States
Greg Mullholland
Affiliation:
mulholland@kymatech.com, Kyma Tech, Raleigh, North Carolina, United States
Keith R. Evans
Affiliation:
evans@kymatech.com, Kyma Tech, Raleigh, North Carolina, United States
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Abstract

For light emitting diodes (LEDs) to be used for general lighting, high efficiencies would need to be retained at high injection levels to meet the intensity and efficiency requirements. In this regard, it is imperative to overcome the observed drop in LED efficiency at high injection levels beyond that would be expected from junction temperature. The suggested genesis of efficiency degradation includes electron overflow or spillover, also suggested to be aided by polarization induced electric field, Auger recombination, current crowding, and elevated junction temperature. Setting the junction temperature aside, the degree to which or even whether each of these mechanisms plays a role is still under debate. We have undertaken a series of experiments to isolate, whenever possible, the aforementioned processes in an effort to determine the causes of efficiency loss at high injection levels. By using 1μs pulsed electrical injection with 0.1% duty cycle, we were able to minimize the effect of the junction temperature. By changing the design of the multiple quantum well region as well as by employing or not employing electron blocking layers, we demonstrated the important role that electron overflow plays on efficiency. Furthermore, by also exploring the same on non polar surfaces and observing any lack of dispersion in terms of the effect of the electron blocking layer we can conclude that the polarization induced field does not seem to play a major role. LEDs on non polar surface with no notable efficiency degradation, up to current densities of about 2250 Acm-2 used for measurements, have been obtained which seems to imply that Auger recombination up to these injection levels is not of major importance, at least in the structures investigated. The effect of current crowding on efficiency droop was investigated by comparing semitransparent Ni/Au p-contacts and transparent conducting oxide contacts (Ga-doped ZnO). Because the latter showed notably reduced efficiency degradation at high injection levels, we can conclude that current crowding plays a role as well.

Keywords

luminescenceoptical propertiesepitaxy
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1202: Symposium I – III-Nitride Materials for Sensing, Energy Conversion and Controlled Light-Matter Interactions , 2009 , 1202-I02-06
Copyright
Copyright © Materials Research Society 2010

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