The optical and structural properties of InGaN epilayers with very high indium content

Bayliss, S. C.; Demeester, Piet; Fletcher, I; Martin, Robert; Middleton, P. G.; Moerman, Ingrid; O’Donnell, K. P.; Sapelkin, Andrei V.; Trager‐Cowan, C.; Stricht, W. Van der; Young, Colin L.

doi:10.1016/s0921-5107(98)00358-4

Cited by 17 publications

(13 citation statements)

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“…23 Furthermore, there is some experimental evidence from structural measurements that indium concentration fluctuations occur on a variety of distance scales and are possibly fractal. 3,24 According to theoretical models, ␤ ϭ0.59 is consistent with a fractal dimension of 1.18. 25 We note that preliminary time-resolved PL measurements on LEDs with ten InGaN layers using a Ti-sapphire oscillator for excitation yielded similar results.…”

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confidence: 67%

Time-resolved photoluminescence measurements of InGaN light-emitting diodes

Pophristić

Long

Tran³

et al. 1998

Applied Physics Letters

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confidence: 67%

Time-resolved photoluminescence measurements of InGaN light-emitting diodes

Pophristić

Long

Tran³

et al. 1998

Applied Physics Letters

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“…In the InGaN alloy system, very large Urbach energies E U of few hundreds of meV have been observed, [8][9][10] attributed to phase separation of the InGaN alloy. This is to be contrasted with the luminescence linewidth in LED materials which is most often quite smaller, of the order of 100 meV or less.…”

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confidence: 99%

Localization landscape theory of disorder in semiconductors. II. Urbach tails of disordered quantum well layers

Piccardo

et al. 2017

Phys. Rev. B

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Urbach tails in semiconductors are often associated to effects of compositional disorder. The Urbach tail observed in InGaN alloy quantum wells of solar cells and LEDs by biased photocurrent spectroscopy is shown to be characteristic of the ternary alloy disorder. The broadening of the absorption edge observed for quantum wells emitting from violet to green (indium content ranging from 0 to 28%) corresponds to a typical Urbach energy of 20 meV. A 3D absorption model is developed based on a recent theory of disorder-induced localization which provides the effective potential seen by the localized carriers without having to resort to the solution of the Schrödinger equation in a disordered potential. This model incorporating compositional disorder accounts well for the experimental broadening of the Urbach tail of the absorption edge. For energies below the Urbach tail of the InGaN quantum wells, type-II well-to-barrier transitions are observed and modeled. This contribution to the below bandgap absorption is particularly efficient in near-UV emitting quantum wells. When reverse biasing the device, the well-to-barrier below bandgap absorption exhibits a red shift, while the Urbach tail corresponding to the absorption within the quantum wells is blue shifted, due to the partial compensation of the internal piezoelectric fields by the external bias. The good agreement between the measured Urbach tail and its modeling by the new localization theory demonstrates the applicability of the latter to compositional disorder effects in nitride semiconductors.

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“…Analysis of x-ray absorption fine structure oscillations can provide structural information on the nanometer scale. When used to probe the local environment of indium atoms within InGaN layers on a next-nearest-neighbor scale, this technique has indicated phase segregation into nanometer size quantum dots and metallic clusters [20,21].…”

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confidence: 99%

Origin of Luminescence from InGaN Diodes

1999

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We report the first direct observation of phase decomposition in a luminescent alloy and show that this decomposition, allied to quantum confinement enhancements, accounts for the surprisingly high efficiency of InGaN-based diodes manufactured by Nichia Chemical Industries. Hence nanostructure, rather than composition, is responsible for the success of these devices. A common nanostructure, in the form of nearly pure InN quantum dots, occurs across a large range of average indium content in InGaN and leads to a universal scalability of the optical spectra. [S0031-9007(98)08055-7] PACS numbers: 85.60. Jb, 78.66.Fd, 85.30.Vw While Nichia Chemical Industries have recently commercialized blue and green light-emitting diodes (LEDs) based upon InGaN quantum wells [1,2], and demonstrated long-lived blue lasers at room temperature [3], rather little is known about the origin of the luminescence from such devices, or its apparent indifference to a huge density of structural defects [4]. Much of the discussion of the operational characteristics of Nichia diodes contradicts a theoretical demonstration [5] that In is, to a large extent, insoluble in GaN at typical growth temperatures. Hence the emission spectrum of, say, a "50% alloy of InGaN grown at 700 ± C" should actually contain two components at high and low energy, corresponding to the twocomponent phase decomposition demanded by thermodynamics. This decomposition of the emission spectrum has been observed for the first time in Nichia diode electroluminescence spectra. In addition, we observe a shift of the low-energy component due to quantum confinement in nanocrystalline inclusions of nearly pure InN, which leads to a dominant emission band in the blue or green spectral region.Although (partial) phase segregation has been shown to be present in InGaN alloys by a number of authors [6-8], we argue here that cation segregation takes an extreme form in Nichia diodes, and find that the origin of the luminescence in these devices is best described as emission from quantum dots of approximately constant composition-approaching InN-and having radii that increase monotonically with the average In incorporation.The intimate connection between exciton localization and luminescence in semiconductors is now well established. Luminescence occurs when the dwell time of an exciton in a localized site exceeds its radiative decay time. The process of luminescence therefore involves an exchange of energy between a massive stationary particle (the exciton) and a massless particle traveling out of the semiconductor at the speed of light (the photon). The interaction is well described in systems without disorder by the polariton model, but it should be noted that each luminescence event involves at least one defect, in the form of a surface. Since excitation, in contrast to luminescence, maps the joint density of states (JDOS), there is an energy shift (usually called the Stokes' shift) between peaks of luminescence and absorption in solid state systems with spatial energy disorder (s...

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The optical and structural properties of InGaN epilayers with very high indium content

Cited by 17 publications

References 4 publications

Time-resolved photoluminescence measurements of InGaN light-emitting diodes

Time-resolved photoluminescence measurements of InGaN light-emitting diodes

Localization landscape theory of disorder in semiconductors. II. Urbach tails of disordered quantum well layers

Origin of Luminescence from InGaN Diodes

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