Effect of alloy fluctuations on the local polarization in nitride nanostructures

Miguel, A.; Schulz, Stefan; O’Reilly, Eoin P.

doi:10.1002/pssb.201100402

Cited by 6 publications

(13 citation statements)

References 13 publications

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“…In order to compute the local polarization potential and overcome these limitations, we have previously used a point dipole model. 4 Here we give the details of our model and extend it, as well as assess its limitations and degree of validity for calculations involving a position-dependent value of the polarization.…”

Section: Point Dipole Methods For the Calculation Of The Polarizamentioning

confidence: 99%

“…In a system where the density of dipoles n p is approximately constant, for instance one dipole located at each cation site in Ref. 4, the number of dipoles δN p contributing to Eq. (B9) located at distances between R and R + δR from r is proportional to the surface area of a sphere of radius R:…”

Section: Computational Aspects: Methods Of Layers and Application To Qmentioning

confidence: 99%

“…To overcome this limitation, we will assume for the nitrides, and InGaN in particular, that the Born effective charge of the cations in the alloy remains the same as for the binary, and that the spherical approximation still holds. 4 We have devised two tests in order to establish how good this approximation is. First, we will use the smallest alloy cell, which is a CuPt-like (CPlike) InGaN unit cell consisting only of 4 atoms, 4,30 and will perform random distortions of the atomic positions within the unit cell.…”

Section: Local Polarization In Ingan Alloys: Strategies and Testingmentioning

confidence: 99%

“…In the description of local polarization that we have previously employed, the values of P were given at the sites of each of the cations present in the crystal. 4 The latter is a useful description, in the sense that the representation of the whole crystal as a collection of deformed tetrahedra can be done via the relative positioning of the nearest neighbors: each cation and its four neighboring anions unambiguously define each tetrahedron. Labeling the anions immediately surrounding a cation as 1, 2, 3 and 4 ( Fig.…”

Section: A From Polarization To Dipole Momentmentioning

confidence: 99%

“…Electrostatic built-in fields arising from discontinuities of the electric polarization vector significantly modify the electronic and optical properties of semiconductor nanostructures. [1][2][3][4] Of particular interest are systems such as GaAs-based quantum dots (QDs), whose electronic and optical properties are affected by the symmetry of strain and strain-induced piezoelectric fields. 5,6 The effect of built-in electrostatic fields is even more dramatic in III-N-based heterostructures, where the large piezoelectric response together with the intrinsic spontaneous polarization give rise to built-in electrostatic fields far exceeding those encountered for other III-V materials.…”

Section: Introductionmentioning

confidence: 99%

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Theory of local electric polarization and its relation to internal strain: Impact on polarization potential and electronic properties of group-III nitrides

Schulz²,

2013

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We present a theory of local electric polarization in crystalline solids and apply it to study the case of wurtzite group-III nitrides. We show that a local value of the electric polarization, evaluated at the atomic sites, can be cast in terms of a summation over nearest-neighbor distances and Born effective charges. Within this model, the local polarization shows a direct relation to internal strain and can be expressed in terms of internal strain parameters. The predictions of the present theory show excellent agreement with a formal Berry phase calculation for random distortions of a test-case CuPt-like InGaN alloy and InGaN supercells with randomly placed cations. While the present level of theory is appropriate for highly ionic compounds, such as III-N materials, we show that a more complex model is needed for less ionic materials, such as GaAs, in which the strain dependence of Born effective charges has to be taken into account. Moreover, we provide ab initio parameters for GaN, InN and AlN, including hybrid functional values for the piezoelectric coefficients and the spontaneous polarization, which we use to accurately implement the local theory expressions. In order to calculate the local polarization potential, we also present a point dipole method. This method overcomes several limitations related to discretization and resolution which arise when obtaining the local potential by solving Poisson's equation on an atomic grid. Finally, we perform tight-binding supercell calculations to assess the impact of the local polarization potential arising from alloy fluctuations on the electronic properties of InGaN alloys. In particular, we find that the large upward bowing with composition of the InGaN valence band edge is strongly influenced by local polarization effects. Furthermore, our analysis allows us to extract composition-dependent bowing parameters for the energy gap and valence and conduction band edges. *

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Section: Point Dipole Methods For the Calculation Of The Polarizamentioning

confidence: 99%

Section: Computational Aspects: Methods Of Layers and Application To Qmentioning

confidence: 99%

Section: Local Polarization In Ingan Alloys: Strategies and Testingmentioning

confidence: 99%

Section: A From Polarization To Dipole Momentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Theory of local electric polarization and its relation to internal strain: Impact on polarization potential and electronic properties of group-III nitrides

Schulz²,

2013

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Analysis of Reduced Built-In Polarization Fields and Electronic Structure of InGaN/GaN Quantum Dot Molecules

Schulz¹,

O’Reilly

2013

Lecture Notes in Nanoscale Science and Technology

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Perspective: Theory and simulation of highly mismatched semiconductor alloys using the tight-binding method

Broderick,

O’Reilly,

Schulz

2024

Journal of Applied Physics

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The electronic structure of highly mismatched semiconductor alloys is characterized by carrier localization and strongly influenced by the local alloy microstructure. First-principles calculations can deliver valuable quantitative insight, but their associated computational expense limits alloy supercell size and imposes artificial long-range ordering, which can produce misleading results. The empirical tight-binding method (ETBM) provides a transparent approach to investigate large-scale supercells on an atomistic level, to quantitatively predict the electronic structure of semiconductor alloys. Here, we overview key aspects and considerations for establishing ETBMs. Additionally, we discuss and highlight, given that the ETBM matrix elements are described in the language of overlaps between localized atomic orbitals, that ETBMs have proven highly successful in analyzing the impact of localized and resonant impurity states, as well as disorder, on the optoelectronic properties of highly mismatched alloys. The ETBM continues to provide valuable insight for emerging material systems, including two-dimensional materials, perovskites and their heterostructures, and provides a framework to address technologically relevant questions including the importance of short-range disorder for loss mechanisms such as non-radiative Auger–Meitner recombination. Moreover, the ETBM furnishes a quantitative basis for continuum models such as k⋅p or localization landscape theories, allowing to explicitly incorporate disorder effects in nanostructures to underpin predictive device-level analysis.

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Effect of alloy fluctuations on the local polarization in nitride nanostructures

Cited by 6 publications

References 13 publications

Theory of local electric polarization and its relation to internal strain: Impact on polarization potential and electronic properties of group-III nitrides

Theory of local electric polarization and its relation to internal strain: Impact on polarization potential and electronic properties of group-III nitrides

Analysis of Reduced Built-In Polarization Fields and Electronic Structure of InGaN/GaN Quantum Dot Molecules

Perspective: Theory and simulation of highly mismatched semiconductor alloys using the tight-binding method

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