Tunability of InGaN/GaN quantum well light emitting diodes through current
TL;DR: In this article, the authors introduced the tunability of an InGaN/GaN quantum well (QW) light emitting diodes (LEDs) having a well width of 4'nm and In mole fraction of 0.3.
Abstract: In the recent years, InGaN/GaN quantum well (QW) light emitting diodes (LEDs) have gathered much importance through the introduction of white LEDs and dual wavelength LEDs. However, the continuous tunability of InGaN/GaN QW LEDs has not been well addressed or discussed. In this paper, we introduce the tunability of an InGaN/GaN QW LED having a well width of 4 nm and In mole fraction of 0.3. The results, obtained from self-consistent solutions of the Schrodinger and Poisson equations, show that the transition energy of the LED may be continuously tuned by the device current. A prominent nonlinearity of the transition energy with the device current is generated, which should be of interest to the research workers in the field of optoelectronics.
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TL;DR: In this article, different forms of the staggered QW; single sided and symmetric, with different Indium compositions in the well, have been studied comprehensively, and the best results are obtained for the symmetrically staggered QWs, where the overlap increases even up to three times that of the rectangular QW and using this structure the operating current may be decreased by more than two orders of magnitude to obtain the same transition energy.
16 citations
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TL;DR: In this article, a comprehensive and systematic studies on InGaN/InGaN quantum well light emitting diodes reveal that the overlap of electron and hole wave functions can be increased even at low operating currents by the introduction of In in the barriers.
16 citations
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TL;DR: In this article, a detailed investigation has been carried out through the selfconsistent solutions of the Schrodinger and Poisson equations to elucidate the change of the emission energy and the transition probability with the operating current and explore how the changes depend on the well width of the QW and the In mole fraction.
11 citations
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TL;DR: In this paper, the authors studied the transition energy, overlap of electron and hole wave functions, band structures and field distributions of the parabolic QW LEDs through self consistent solutions of Schrodinger and Poisson equations.
Abstract: The strong piezoelectric field in the InxGa1−xN/GaN quantum well (QW) LEDs, separates the electrons and holes spatially, which decreases the luminescence. Various shapes and compositions of such QWs are studied to improve the performance. We have studied the transition energy (TE), overlap of electron and hole wave functions, band structures and field distributions of the parabolic QWs (PQW) through the self consistent solutions of Schrodinger and Poisson equations. The shape of the PQW is varied along with the compositions and dopings. The square of the overlap of electron and hole wave functions i.e. the transition probability (TP) is strikingly increased, compared to the rectangular QW and it is even higher than the symmetrically staggered QW. At a particular current density, for the same TE, the TP of the PQW increases more than two times that of the rectangular QWs. An important feature, desirable for the QW LEDs emerge. The change of the TE with increase in the current density is minimized. A brief theory, computational procedures and the results will be presented in details with suitable discussions.
9 citations
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TL;DR: In this paper, the incorporation of Indium (In) in the GaN barrier layers, with an aim of increasing the overlap of electron and hole wave functions, has been investigated.
Abstract: Although that the continuous tunability of InGaN/GaN QW LEDs, carries the promise of a significant impact in optoelectronics, the reduction of the square of the overlap of electron and hole wave functions ( M e h 2 ) in InGaN/GaN QW LEDs, under certain conditions, is a sizable problem, difficult to overcome. Theoretical investigations have been carried out on the incorporation of Indium (In) in the GaN barrier layers, with an aim of increasing the overlap of electron and hole wave functions. Rigorous studies through the self consistent solution of Schrodinger and Poison equations expose some new and striking results. With suitable doping, the inclusion of In in the barriers can increase M e h 2 to more than two times that of a conventional InGaN/GaN QW LED. In in the barrier along with doping may be suitably utilized to tailor the transition energy and M e h 2 with current density, as desired. The transition energy and the M e h 2 may be made to have a positive or a negative slope with current density or they may be made fairly constant. This paper will outline the theoretical details, computational methodologies, the parameters used, and the striking new results with suitable depictions and discussions. These new information ought to be interesting for current optoelectronics.
6 citations
References
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TL;DR: In this paper, the bandgap of InN was revised from 1.9 eV to a much narrower value of 0.64 eV, which is the smallest bandgap known to date.
Abstract: Wide-band-gap GaN and Ga-rich InGaN alloys, with energy gaps covering the blue and near-ultraviolet parts of the electromagnetic spectrum, are one group of the dominant materials for solid state lighting and lasing technologies and consequently, have been studied very well. Much less effort has been devoted to InN and In-rich InGaN alloys. A major breakthrough in 2002, stemming from much improved quality of InN films grown using molecular beam epitaxy, resulted in the bandgap of InN being revised from 1.9 eV to a much narrower value of 0.64 eV. This finding triggered a worldwide research thrust into the area of narrow-band-gap group-III nitrides. The low value of the InN bandgap provides a basis for a consistent description of the electronic structure of InGaN and InAlN alloys with all compositions. It extends the fundamental bandgap of the group III-nitride alloy system over a wider spectral region, ranging from the near infrared at ∼1.9 μm (0.64 eV for InN) to the ultraviolet at ∼0.36 μm (3.4 eV for GaN...
871 citations
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TL;DR: In this paper, the authors provide a snapshot of the current state of droop research, reviews currently discussed droop mechanisms, contextualizes them, and proposes a simple yet unified model for the LED efficiency droop.
Abstract: Nitride-based light-emitting diodes (LEDs) suffer from a reduction (droop) of the internal quantum efficiency with increasing injection current. This droop phenomenon is currently the subject of intense research worldwide, as it delays general lighting applications of GaN-based LEDs. Several explanations of the efficiency droop have been proposed in recent years, but none is widely accepted. This feature article provides a snapshot of the present state of droop research, reviews currently discussed droop mechanisms, contextualizes them, and proposes a simple yet unified model for the LED efficiency droop.
Illustration of LED efficiency droop (details in Fig. 13).
778 citations
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TL;DR: In this paper, the nonlinear polarization for nitride alloys of arbitrary composition was calculated, and the bound sheet charge induced by polarization discontinuity at the interfaces between different alloy and binary (epi) layers.
Abstract: We provide explicit rules to calculate the nonlinear polarization for nitride alloys of arbitrary composition, and hence, the bound sheet charge induced by polarization discontinuity at the interfaces between different alloy and binary (epi)layers. We then present experimental results and simulations of polarization-related quantities in selected nitride-alloy-based heterostructure systems. The agreement of experiment and simulation, also in comparison to previous approaches, strongly suggests that the macroscopic polarization of nitride alloys is indeed nonlinear as a function of composition.
750 citations
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TL;DR: In this paper, a selfconsistent, one-dimensional solution of the Schrodinger and Poisson equations is obtained using the finite-difference method with a nonuniform mesh size.
Abstract: A self‐consistent, one‐dimensional solution of the Schrodinger and Poisson equations is obtained using the finite‐difference method with a nonuniform mesh size. The use of the proper matrix transformation allows preservation of the symmetry of the discretized Schrodinger equation, even with the use of a nonuniform mesh size, therefore reducing the computation time. This method is very efficient in finding eigenstates extending over relatively large spatial areas without loss of accuracy. For confirmation of the accuracy of this method, a comparison is made with the exactly calculated eigenstates of GaAs/AlGaAs rectangular wells. An example of the solution of the conduction band and the electron density distribution of a single‐heterostructure GaAs/AlGaAs is also presented.
674 citations
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TL;DR: In this article, the optical absorption edge covers a wide energy range from the intrinsic band gap of InN of about 0.7 to about 1.7 eV which is close to the previously accepted band gap.
Abstract: InN films with free electron concentrations ranging from mid-1017 to mid-1020 cm−3 have been studied using optical absorption, Hall effect, and secondary ion mass spectrometry. The optical absorption edge covers a wide energy range from the intrinsic band gap of InN of about 0.7 to about 1.7 eV which is close to the previously accepted band gap of InN. The electron concentration dependence of the optical absorption edge energy is fully accounted for by the Burstein–Moss shift. Results of secondary ion mass spectrometry measurements indicate that O and H impurities cannot fully account for the free electron concentration in the films.
222 citations