Energy and Climate
Energy and ClimateRenewable SystemsEnergy EfficiencySolid-State Lighting Science EFRCOur SSLS EFRC’s Scientific Research Challenges and PublicationsResearch Challenge 3: Competing Radiative and Nonradiative Processes

Research Challenge 3: Competing Radiative and Nonradiative 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.
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Conduction and valence band profile of an InGan multiple quantum well (MQW) LED active regions including GaN barrier modification due to polarization fields and Si doping. Dominant emission is from the rightmost (p-side) QW.

Our study of these competing physical processes involves both experiment and theory, with a particular current focus on carrier-density and polarization-field impacts 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.

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Model predictions of effective radiative coefficient (B) and loss due to carrier capture and relaxation via phonon emission (heating) versus current density for violet and green LEDs. Increased loss due to heating and lower B coefficient are factors that reduce efficiency for green LEDs.

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 nonradiative 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 Scientific 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

  • Cho, Jaehee; Schubert, E. Fred; and Kim, Jong Kyu Efficiency droop in light-emitting diodes: Challenges and countermeasures, Laser Photonics Rev., (2012). [10.1002/lpor.201200025]
  • Lin, Guan-Bo; Shan, Qifeng; Birkel, Andrew J.; Cho, Jaehee; Schubert, E. Fred; Crawford, Mary H.; Westlake, Karl R.; and Koleske, Daniel D. Method for determining the radiative efficiency of GaInN quantum wells based on the width of efficiency-versus-carrier-concentration curve, Appl. Phys. Lett., 101, 241104 (2012). [10.1063/1.4770317]
  • Ma, Ming; Cho, Jaehee; Schubert, E. Fred; Park, Yongjo; Kim, Gi Bum; and Sone, Cheolsoo Strong light-extraction enhancement in GaInN light-emitting diodes patterned with TiO2 micro-pillars with tapered sidewalls, Applied Physics Letters, 101, 141105 (2012). [10.1063/1.4756797]
  • Shan, Qifeng; Cho, Yong Suk; Lin, Guan-Bo; Meyaard, David S.; Cho, Jaehee; Schubert, E. Fred; Son, Joong Kon; and Sone, Cheolsoo Analysis of parasitic cyan luminescence occurring in GaInN blue light-emitting diodes, Journal of Applied Physics, 112, 074512 (2012). [10.1063/1.4754829]
  • Ma, Ming; Meyaard, David S.; Shan, Qifeng; Cho, Jaehee; Schubert, E. Fred; Kim, Gi Bum; Kim, Min-Ho; and Sone, Cheolsoo Polarized light emission from GaInN light-emitting diodes embedded with subwavelength aluminum wire-grid polarizers, Applied Physics Letters, 101, 061103 (2012). [10.1063/1.4744422]
  • Mont, Frank W.; Fischer, Arthur J.; Noemaun, A. N.; Poxson, David J.; Cho, Jaehee; Schubert, E. Fred; Crawford, Mary H.; Koleske, Daniel D.; and Fullmer, Kristine W. Enhanced light-extraction from a GaN waveguide using micro-pillar TiO2–SiO2 graded-refractive-index layers, Phys. Status Solidi A, 209, 2277 (2012). [10.1002/pssa.201228295]
  • Ma, Ming; Noemaun, A. N.; Cho, Jaehee; Schubert, E. Fred; Kim, Gi Bum; and Sone, Cheolsoo Emission pattern control and polarized light emission through patterned graded-refractiveindex coatings on GaInN light-emitting diodes, Optics Express, 20, 16677 (2012). [10.1364/OE.20.016677]
  • Lin, Guan-Bo; Meyaard, David S.; Cho, Jaehee; Schubert, E. Fred; Shim, Hyunwook; and Sone, Cheolsoo Analytic model for the efficiency droop in semiconductors with asymmetric carrier-transport properties based on drift-induced reductin of injection efficiency, Applied Physics Letters, 100, 161106 (2012). [10.1063/1.4704366]
  • Shim, Jong-Im; Han, Dong-Pyo; Kim, Hyunsung; Shin, Dong-Soo; Lin, Guan-Bo; Meyaard, David S.; Shan, Qifeng; Cho, Jaehee; Schubert, E. Fred; Shim, Hyunwook; and Sone, Cheolsoo Efficiency droop in AlGaInP and GaInN light-emitting diodes, Applied Physics Letters, 100, 111106 (2012). [10.1063/1.3694044]
  • Zhu, Di; Schubert, Martin F.; Xu, Jiuru; Cho, Jaehee; Schubert, E. Fred; Crawford, Mary H.; and Koleske, Daniel D. Genetic algorithm for innovative designs in high efficiency III-V nitride light-emitting diodes, Applied Physics Express, 5, 012102 (2012). [10.1143/APEX.5.012102]
  • 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]
  • Chow, Weng W. Modeling excitation-dependent bandstructure effects on InGaN light-emitting diode efficiency, Optics Express, 19, 21818 (2011). [10.1364/OE.19.021818]
  • Xu, Jiuru; Schubert, Martin F.; Zhu, Di; Cho, Jaehee; Schubert, E. Fred; Shim, Hyunwook; and Sone, Cheolsoo Effects of plarization-field tuning in GaInN light-emitting diodes, Applied Physics Letters, 99, 041105 (2011). [10.1063/1.3609783]
  • 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]
  • 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). [10.1889/JSID19.6.431]
  • 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, Appl. Phys. Lett., 98, 033506 (2011). [10.1063/1.3544584 ]
  • 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, Appl. Phys. Lett., 97, 121105 (2010). [10.1063/1.3490232]
  • 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, Appl. Phys. Lett., 97, 133507 (2010). [10.1063/1.3493654]
  • Schubert, Martin F.; and Schubert, E. Fred Effect of heterointerface polarization charges and well width upon capture and dwell time for electrons and holes above GaInN/GaN quantum wells, Appl. Phys. Lett., 96, 131102 (2010). [10.1063/1.3373610]
  • 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, Appl. Phys. Lett., 96, 121110 (2010). [10.1063/1.3371812]
  • Tsao, Jeffrey Y.; Brener, Igal; Kelley, David F.; and Lyo, S. Ken Quantum-Dot-Based Solid-State Lighting With Electric-Field-Tunable Chromaticity, J. Disp. Technol., (2012). [10.1109/JDT.2012.2225407]
  • Lyo, S. Ken Photon-exchange energy transfer of an electron-hole plasma between quasi-two-dimensional semiconductor layers, Journal of Luminescence, 132, 3035 (2012). [10.1016/j.jlumin.2012.06.033]
  • Armstrong, Andrew; Henry, Tania A.; Koleske, Daniel D.; Crawford, Mary H.; Westlake, Karl R.; and Lee, Stephen R. Dependence of radiative efficiency and deep level defect incorporation on threading dislocation density for InGaN/GaN light emitting diodes, Applied Physics Letters, 101, 162102 (2012). [10.1063/1.4759003]
  • Armstrong, Andrew; Henry, Tania A.; Koleske, Daniel D.; Crawford, Mary H.; and Lee, Stephen R. Quantitative and depth-resolved deep level defect distributions in InGaN/GaN light emitting diodes, Optics Express, 20, A812-A821 (2012). [10.1364/OE.20.00A812]
  • Armstrong, Andrew; Crawford, Mary H.; and Koleske, Daniel D. Quantitative and Depth-Resolved Investigation of Deep-Level Defects in InGaN/GaN Heterostructures, J. Electron. Mater., 40, 369 (2011). [10.1007/s11664-010-1453-4]

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