Role of defects in the thermal droop of InGaN-based light emitting diodes
01 Mar 2016-Journal of Applied Physics (American Institute of Physics Inc.)-Vol. 119, Iss: 9, pp 094501
TL;DR: In this article, the authors investigated the role of various mechanisms including Shockley-Read-Hall recombination, thermionic escape from the quantum well, phonon assisted tunneling, and thermionic trap-assisted tunneling; in addition, to explain the thermal droop, they proposed a closed-form model which is able to accurately fit the experimental data by using values extracted from measurements and simulations and a limited set of fitting parameters.
Abstract: This paper reports an investigation of the physical origin of the thermal droop (the drop of the optical power at high temperatures) in InGaN-based light-emitting diodes. We critically investigate the role of various mechanisms including Shockley-Read-Hall recombination, thermionic escape from the quantum well, phonon-assisted tunneling, and thermionic trap-assisted tunneling; in addition, to explain the thermal droop, we propose a closed-form model which is able to accurately fit the experimental data by using values extracted from measurements and simulations and a limited set of fitting parameters. The model is based on a two-step phonon-assisted tunneling over an intermediate defective state, corrected in order to take into account the pure thermionic component at zero bias and the field-assisted term.
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References
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TL;DR: In this article, the statistics of the recombination of holes and electrons in semiconductors were analyzed on the basis of a model in which the recombinations occurred through the mechanism of trapping.
Abstract: The statistics of the recombination of holes and electrons in semiconductors is analyzed on the basis of a model in which the recombination occurs through the mechanism of trapping. A trap is assumed to have an energy level in the energy gap so that its charge may have either of two values differing by one electronic charge. The dependence of lifetime of injected carriers upon initial conductivity and upon injected carrier density is discussed.
5,442 citations
TL;DR: In this paper, a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III-V semiconductors that have been investigated to date is presented.
Abstract: We present a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III–V semiconductors that have been investigated to date. The two main classes are: (1) “conventional” nitrides (wurtzite and zinc-blende GaN, InN, and AlN, along with their alloys) and (2) “dilute” nitrides (zinc-blende ternaries and quaternaries in which a relatively small fraction of N is added to a host III–V material, e.g., GaAsN and GaInAsN). As in our more general review of III–V semiconductor band parameters [I. Vurgaftman et al., J. Appl. Phys. 89, 5815 (2001)], complete and consistent parameter sets are recommended on the basis of a thorough and critical review of the existing literature. We tabulate the direct and indirect energy gaps, spin-orbit and crystal-field splittings, alloy bowing parameters, electron and hole effective masses, deformation potentials, elastic constants, piezoelectric and spontaneous polarization coefficients, as well as heterostructure band offsets. Temperature an...
2,525 citations
TL;DR: In this paper, the Auger recombination coefficient in quasi-bulk InxGa1−xN (x∼9%−15%) layers grown on GaN (0001) is measured by a photoluminescence technique.
Abstract: The Auger recombination coefficient in quasi-bulk InxGa1−xN (x∼9%–15%) layers grown on GaN (0001) is measured by a photoluminescence technique. The samples vary in InN composition, thickness, and threading dislocation density. Throughout this sample set, the measured Auger coefficient ranges from 1.4×10−30to2.0×10−30cm6s−1. The authors argue that an Auger coefficient of this magnitude, combined with the high carrier densities reached in blue and green InGaN∕GaN (0001) quantum well light-emitting diodes (LEDs), is the reason why the maximum external quantum efficiency in these devices is observed at very low current densities. Thus, Auger recombination is the primary nonradiative path for carriers at typical LED operating currents and is the reason behind the drop in efficiency with increasing current even under room-temperature (short-pulsed, low-duty-factor) injection conditions.
1,124 citations
TL;DR: The droop phenomenon in GaN light-emitting diodes originates from the excitation of Auger processes, which shows that hot carriers are being generated in the active region (InGaN quantum wells) by an Auger process.
Abstract: We report on the unambiguous detection of Auger electrons by electron emission spectroscopy from a cesiated $\mathrm{InGaN}/\mathrm{GaN}$ light-emitting diode under electrical injection. Electron emission spectra were measured as a function of the current injected in the device. The appearance of high energy electron peaks simultaneously with an observed drop in electroluminescence efficiency shows that hot carriers are being generated in the active region (InGaN quantum wells) by an Auger process. A linear correlation was measured between the high energy emitted electron current and the ``droop current''---the missing component of the injected current for light emission. We conclude that the droop phenomenon in GaN light-emitting diodes originates from the excitation of Auger processes.
592 citations
TL;DR: In this paper, the free-carrier effects in GaN were derived by studying the normal-incidence reflectance as a function of carrier concentration in the 2.17-to 1.20-folding range.
Abstract: Infrared reflectivity and absorption measurements have been made on single-crystal epitaxial GaN on (0001) $\ensuremath{\alpha}\ensuremath{-}$${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ crystals. Analysis of the normal-incidence reflectance data on low-carrier-concentration layers using the Kramers-Kronig technique and dielectric oscillator fits yields the values ${\ensuremath{\omega}}_{\mathrm{TO}}^{\ensuremath{\perp}}=560$ ${\mathrm{cm}}^{\ensuremath{-}1}$ and ${\ensuremath{\omega}}_{\mathrm{LO}}^{\ensuremath{\perp}}=746$ ${\mathrm{cm}}^{\ensuremath{-}1}$ for the optical mode frequencies at 300 K. Adopting ${\ensuremath{\epsilon}}_{\ensuremath{\infty}}^{\ensuremath{\perp}}=5.35$ from a fit to Ejder's refractive-index data the additional quantities ${\ensuremath{\epsilon}}_{o}^{\ensuremath{\perp}}=9.5$ for the static dielectric constant, ${e}_{B}^{*\ensuremath{\perp}}=2.65e$ for the Born effective charge, and ${\ensuremath{\alpha}}^{\ensuremath{\perp}}=0.44$ for the polaron coupling constant are derived. Reflectivity measurements at 50\ifmmode^\circ\else\textdegree\fi{} incidence with $s$ and $p$ polarizations show that the longitudinal lattice mode is nearly isotropic. Using the value ${\ensuremath{\omega}}_{\mathrm{TO}}^{\ensuremath{\parallel}}=533$ ${\mathrm{cm}}^{\ensuremath{-}1}$ from Raman data the values ${\ensuremath{\omega}}_{\mathrm{LO}}^{\ensuremath{\parallel}}=744$ ${\mathrm{cm}}^{\ensuremath{-}1}$, ${\ensuremath{\epsilon}}_{o}^{\ensuremath{\parallel}}=10.4$, ${e}_{B}^{*\ensuremath{\parallel}}=2.82e$, and ${\ensuremath{\alpha}}^{\ensuremath{\parallel}}=0.49$ are obtained from oscillator fits to the 50\ifmmode^\circ\else\textdegree\fi{} incidence data. Information on the free-carrier effects in GaN was obtained by studying the normal-incidence reflectance as a function of carrier concentration in the 2\ifmmode\times\else\texttimes\fi{}${10}^{17}$ to 1\ifmmode\times\else\texttimes\fi{}${10}^{20}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ range. By fitting the reflectance minima versus concentration data, a value of $\frac{{m}^{*}}{m}=(0.20\ifmmode\pm\else\textpm\fi{}0.02)$ for the optical effective mass is obtained. Measurements at 50\ifmmode^\circ\else\textdegree\fi{} incidence show that the plasma frequency is isotropic within experimental precision.
543 citations