Ultrafast Carrier Dynamics and Recombination in Green Emitting InGaN MQW LED
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0916-DD04-10
Ultrafast Carrier Dynamics and Recombination in Green Emitting InGaN MQW LED A. N. Cartwright1, M. C-K. Cheung1, F. Shahedipour-Sandvik2, J. R. Grandusky2, M. Jamil2, V. Jindal2, S. B. Schujman3, L. J. Schowalter3, C. Wetzel4, P. Li5, T. Detchprohm5, and J. S. Nelson5 1 Department of Electrical Engineering, Universisty at Buffalo, The State University of New York, Buffalo, New York, 14260 2 College of Nanoscale Science and Engineering, University at Albany-State University of New York, Albany, New York, 12203 3 Crystal IS Inc., Green Island, New York, 12183 4 Future Chips Constellation, Rensselaer Polytechnic Institute, Troy, New York, 12180 5 Uniroyal Optoelectronics, Tampa, Florida, 33619
ABSTRACT Time-resolved photoluminescence studies can provide useful information for the development of InGaN/GaN heterostructures for long wavelength visible emitters. In this paper, we present results of time-resolved photoluminescence from samples grown using two different approaches to achieve green emission from InGaN/GaN MQWs. In one approach, samples, with high indium incorporation, were grown on a high quality AlN substrate to achieve green emission. The resulting photoluminescence decay of the green luminescence is long-lived and non-exponential. Quantitative analysis showed that the decay has a stretched-exponential characteristic, typical of InGaN/GaN MQW with potential fluctuation along the growth plane. This carrier localization, in a structure with low defect density, proves to be an effective means to achieve green emission. In another approach, a piezoelectric Stark-like ladder effect is used. In this case, a methodical layer-by-layer growth homogeneity optimization process was adopted to achieve an optical transition below the electron to heavy-hole (e1hh1) transition when the quantum well is subjected to the strong piezoelectric polarization dipole. This approach has proven to be successful in achieving green luminescence on conventional sapphire substrates. The resulting photoluminescence decay at 14 K, of a sample grown by this approach, is single exponential and shorter in duration than the decay observed in the first approach. This exponential decay is consistent with previous AFM studies that revealed a homogeneous active region. INTRODUCTION Nitride materials have demonstrated remarkable versatility as light emitting devices. These materials have become the standard for developing UV and visible LED and laser sources [1]. Obviously, the early technological breakthroughs for low indium content InGaN/GaN heterostructures have resulted in successful commercialization. However, deep UV laser sources and long wavelength (red and green) visible emitters remain as major challenges for nitride materials. Remarkably, the recent unexpected discovery of the narrow band gap energy of InN (~0.7 eV) [2-4] provides new opportunities for the application of InGaN ternary alloy as multijunction solar cells [5] and invigorates research efforts to achieve visible to infrared emitters
from the InGaN system. How
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