Research Challenge 3: Competing Radiative and Non-Radiative Processes

Research Challenge 3: Competing Radiative and Non-Radiative Processes

This Research Challenge aims to develop a microscopic understanding of the competing physical processes that determine light-emission efficiency of InGaN materials and heterostructures. With such understanding, new routes to ultra-high light-emission efficiency at all current densities and all across the visible spectrum might be realized, thus overcoming the blue-efficiency and RYG-gap technology challenges.  Along with this would come chromaticity-tunable light, which would also impact higher functionality light.

Our study of these competing physical processes involves both experiment and theory, with a particular current focus on the impact of carrier density and polarization fields on spontaneous emission rates, carrier trapping in, and escape from, quantum wells, and on the limitations to the so-called ABC model commonly used to characterize carrier recombination processes.

Our focus thus far has been on the blue-light-emitting InGaN planar architectures that the current generation of SSL is based on and, in particular, on the efficiency droop phenomenon that plagues these heterostructures. Despite an explosion of work in the past several years, the mechanism for efficiency droop is scientifically unresolved and controversial.

In our work, we are studying two of the most controversial issues. The first issue has to do with the importance of carrier capture and escape from quantum wells, where we are especially trying to understand the role of unequal electron and hole transport and local concentrations. The second issue has to do with suitability of the macroscopic “ABC model” for interpreting LED efficiency data and the unexpectedly high Auger recombination coefficients derived from this approach. We are developing alternative microscopic treatments of the radiative and non-radiative processes to achieve more accurate predictions of dominant recombination mechanisms and efficiency trends in the high-carrier-density regime.

Research Participants

• Dr. Mary Crawford (SNL) – Principal Investigator, coordinates activities, performs spectroscopic studies of InGaN MQW efficiency; contributes to custom-sample designs for efficiency-droop work.
• Dr. Weng Chow (SNL) – Performs bandstructure calculations and recombination modeling of InGaN heterostructures using a custom Sandia-developed code.
• Dr. Daniel Koleske (SNL) – Performs metal-organic vapor phase epitaxial (MOVPE) growth of InGaN.
• Prof. E. Fred Schubert (RPI) – Designs custom samples for efficiency droop studies, performs LED efficiency measurements and modeling of experimental data.

Because this Research Challenge is overarching, it also benefits from staff in most of the other Research Challenges, particularly from Research Challenges 1 (InGaN nanowires), 4 (Defect-Carrier Interactions) and 5 (Enhanced Spontaneous Emission).

We call special attention to the close collaboration with Prof. Fred Schubert (RPI). Prof. Schubert’s group is one of the leading groups studying efficiency droop, particularly the role of carrier transport. RPI graduate students lead experiments for many of our joint projects, employing custom InGaN heterostructures grown, processed and characterized by Sandia. The RPI team further employs LED modeling software and genetic algorithms for data analysis and development of new sample designs. Sandia complements these modeling efforts with microscopic models coupled with spectroscopic efficiency studies.

Research Challenge Publications

Zhu, Di; Schubert, Martin F.; Xu, Jiuru; Cho, Jaehee; Schubert, E. Fred; Crawford, Mary H.; Koleske, Daniel D. Genetic algorithm for innovative designs in high efficiency iii-v nitride light-emitting diodes, Applied Physics Express, Accepted (2012).

Chow, Weng W. Modeling excitation-dependent bandstructure effects on InGaN light-emitting diode efficiency, Optics Express, 19, 21818 (2011). [10.1364/OE.19.021818]

Zhu, Di; Schubert, Martin F.; Xu, Jiuru; Cho, Jaehee; Schubert, E. Fred; Crawford, Mary H.; Koleske, Daniel D. Genetic algorithm for innovative designs in high efficiency iii-v nitride light-emitting diodes, Applied Physics Express, Accepted (2012).

Meyaard, David S.; Lin, Guan-Bo; Shan, Qifeng; Cho, Jaehee; Schubert, E. Fred; Shim, Hyunwook; Kim, Min-Ho; and Sone, Cheolsoo Asymmetry of carrier transport leading to efficiency droop in gainn based light-emitting diodes, Applied Physics Letters, 99, 251115 (2011). [10.1063/1.3671395]

Xu, Jiuru; Schubert, Martin F.; Zhu, Di; Cho, Jaehee; Schubert, E. Fred; Shim, Hyunwook; and Sone, Cheolsoo Effects of pOLArization-field tuning in GaInN light-emitting diodes, Applied Physics Letters, 99, 041105 (2011). [10.1063/1.3609783]

Lin, Guan-Bo; Schubert, Martin F.; Cho, Jaehee; Schubert, E. Fred; and Kim, Hyungkun A complementary matching technique to reduce the variance of optical and electrical properties of light-emitting diodes, Journal of the Society for Information Display, 19, 431 (2011). [10.1063/1.3618673]

Meyaard, David S.; Shan, Qifeng; Dai, Qi; Cho, Jaehee; Schubert, E. Fred; Kim, Min-Ho; and Sone, Cheolsoo On the temperature dependence of electron leakage from the active region of GaInN/GaN light-emitting diodes, Applied Physics Letters, 99, 041112 (2011). [10.1063/1.3618673]

Chhajed, Sameer; Cho, Jaehee; Schubert, E. Fred; Kim, Jong Kyu; Koleske, Daniel D.; and Crawford, Mary H. Temperature-dependent light-output characteristics of GaInN light-emitting diodes with different dislocation densities, Physica Status Solidi A, 208, 947 (2011). [10.1002/pssa.201026668]

Dai, Qi; Shan, Qifeng; Cho, Jaehee; Schubert, E. Fred; Crawford, Mary H.; Koleske, Daniel D.; Kim, Min-Ho; and Park, Yongjo On the symmetry of efficiency-versus-carrier-concentration curves in GaInN/GaN light-emitting diodes and relation to droop-causing mechanisms, Applied Physics Letters, 98, 033506 (2011). [10.1063/1.3544584 ]

Dai, Qi; Shan, Qifeng; Wang, Jing; Chhajed, Sameer; Cho, Jaehee; Schubert, E. Fred; Crawford, Mary H.; Koleske, Daniel D.; Kim, Min-Ho; and Park, Yongjo Carrier recombination mechanisms and efficiency droop in GaInN/GaN light-emitting diodes, Applied Physics Letters, 97, 133507 (2010). [10.1063/1.3493654]

Zhu, D.; Noemaun, A. N.; Schubert, Martin F.; Cho, J.; Schubert, E. Fred; Crawford, Mary H.; and Koleske, Daniel D. Enhanced electron capture and symmetrized carrier distribution in GaInN light-emitting diodes having tailored barrier doping, Applied Physics Letters, 96, 121110 (2010). [10.1063/1.3371812]

Shan, Qifeng; Dai, Qi; Chhajed, Sameer; Cho, Jaehee; and Schubert, E. Fred Analysis of thermal properties of GaInN light-emitting diodes and laser diodes, Journal of Applied Physics, 108, 084504 (2010). [10.1063/1.3493117]

Chow, Weng W.; Crawford, Mary H.; Tsao, Jeffrey Y.; and Kneissl, Michael Internal efficiency of InGaN light-emitting diodes: Beyond a quasiequilibrium model, Applied Physics Letters, 97, 121105 (2010). [10.1063/1.3490232]

Schubert, Martin F.; and Schubert, E. Fred Effect of heterointerface polarization charges and well depth upon capture and dwell time for electrons and holes above GaInN/GaN quantum wells, Applied Physics Letters, 96, 131102 (2010). [10.1063/1.3373610]