Actions for Radiative transitions in InGaN quantum-well structures [electronic resource].

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Radiative transitions in InGaN quantum-well structures [electronic resource].

Published
Washington, D.C. : United States. Dept. of Energy, 2002.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description
vp : digital, PDF file
Additional Creators
Lawrence Berkeley National Laboratory, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information
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Summary
InGaN based light emitting devices demonstrate excellent luminescence properties and have great potential in lighting applications. Though these devices are already being produced on an industrial scale, the nature of their radiative transition is still not well understood. In particular, the role of the huge (>1MV/cm), built-in electric field in these transitions is still under debate. The luminescence characteristics of InGaN quantum well structures were investigated as a function of excitation power, temperature, and biaxial strain, with an intent of discerning the effects of the electric field and inhomogeneous indium distribution in the QW on the radiative transition. It was found that the luminescence energy did not scale only with the indium concentration but that the QW thickness must also be taken into account. The thickness affects the transition energy due to quantum confinement and carrier separation across a potential drop in the QW. The luminescence peak width was shown to increase with increased indium fraction, due to increased indium inhomogeneity. The carrier lifetime increased exponentially with QW thickness and luminescence wavelength, due to increased carrier separation. Measuring the luminescence energy and carrier lifetime as a function of excitation density showed that the electric field can be screened by strong excitation and, as a consequence, the carrier separation reduced. The temperature dependence of the luminescence showed evidence for bandtails in the density of states, a phenomenon that has been previously related to transition in indium-rich nano-clusters, yet could be accounted for by fluctuations in other parameters that affect the transition energy. Room temperature luminescence efficiency was shown to weakly decrease with increased QW thickness. The application of biaxial strain resulted in either a redshift or blueshift of the luminescence, depending on the sample. The direction and magnitude of the shift in luminescence energy is interpreted in terms of a newly introduced parameter L{sub r}, which can be regarded as the effective separation of electrons and holes participating in the luminescence transition. Strong carrier separation due to the built-in electric field usually results in a blueshift and L{sub r} close to the QW width, L{sub w}, whereas weak carrier separation usually can be a redshift. The carrier lifetime decreases with applied strain, indicating a reduction of the effective electron-hole (e-h) separation achieved by the strain-induced field-reduction in the well. This method is used to evaluate the effective e-h separation in several structures with varying QW thickness, indium concentration, and doping. L{sub r} increases with QW thickness, decreases with indium content, and decreases with heavy doping in the active region. The decrease associated with indium content might be due either to an increase of ''carrier trapping'' in indium-rich nano-clusters or to an effective reduction of the QW thickness due to interface diffusion. The decrease of L{sub r} associated with heavy doping is probably due to quenching of the electric field by the free carriers. The results also show that despite the reduced radiative transition rate associated with the carrier separation, the structures still exhibit efficient luminescence behavior and a low non-radiative recombination rate. This suggests that while the carriers are separated along the direction of the electric field, they are localized in the perpendicular direction such that they are not interacting with non-radiative centers associated with the high density of threading dislocations in the structure.
Report Numbers
E 1.99:lbnl--51029
lbnl--51029
Subject(s)
Other Subject(s)
Dissertation Note
Thesis (Ph.D.); Submitted to the University of California, Berkeley, CA (US); PBD: 27 Jun 2002
Note
Published through SciTech Connect.
06/27/2002.
"lbnl--51029"
"B& R KC0201030"
Shapiro, Noad Asaf.
Funding Information
AC03-76SF00098
513330
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