Measurements of the Electric Field of Zero-Point Optical Phonons in GaAs Quantum Wells Support the Urbach Rule for Zero-Temperature Lifetime Broadening

Bhattacharya, Rupak; Mondal, Richarj; Khatua, Pradip; Rudra, A.; Kapon, E.; Malzer, S.; Döhler, G. H.; Pal, Bipul; Bansal, Bhavtosh

doi:10.1103/physrevlett.114.047402

Cited by 18 publications

(14 citation statements)

References 42 publications

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“…An alternate way to characterize the Urbach tail is via the fit to a simple equation α ∼ exp( ω/E u (T )), where E u (T ) is the temperature dependent slope. While our measured values of E u at the lowest temperature are again in excellent agreement with the early data summarized by Pankove where 5 < E u < 10 meV at helium temperature [39], interestingly, they are about four times larger than what was measured on high quality GaAs quantum wells [27] where E u was ≈ 2 meV. This difference, of course, reflects the difference in the excitonic binding energy between bulk and quasitwo dimensional systems.…”

Section: Physics Of the Excitonic Urbach Edgesupporting

confidence: 91%

“…It has long been known that the joint density of states of almost all band insulators has a 'tail' just below the fundamental energy gap. In this bandtail region, the absorption coefficient α( ω, T ) has a universal form given by the Urbach rule [26,27]…”

Section: The Urbach Edgementioning

confidence: 99%

“…Since the bound states are now energetically degenerate with the continuum, the additional lifetime broadening of excitonic resonance manifests as the Urbach lineshape [27,34,37]. each instant in time, essentially sees a snapshot of the distorted lattice [37].…”

Section: Physics Of the Excitonic Urbach Edgementioning

confidence: 99%

“…While there have been some previous attempts [10,25], which we will describe below, the fundamentally difficult nature of this enterprise has resulted in large uncertainties. Here we demonstrate how the low temperature Urbach edge [26,27,28,29,30,31,32,33,34] of a high purity band insulator may be used to directly estimate the bare excitonic gap [27]. .…”

Section: Introductionmentioning

confidence: 97%

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Experimental determination of the bare energy gap of GaAs without the zero-point renormalization

Roy

Mukhuti²,

Bansal³

2019

J. Phys.: Condens. Matter

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The energy gap of simple band insulators like GaAs is a strong function of temperature due to the electron-phonon interactions. Interestingly, the perturbation from zero-point phonons is also predicted to cause significant (a few percent) renormalization of the energy gap at absolute zero temperature but its value has been difficult to estimate both theoretically and, of course, experimentally. Given the experimental evidence [Bhattacharya, et al., Phys. Rev. Lett. 114, 047402 (2015)] that strongly supports that the exponential broadening (Urbach tail) of the excitonic absorption edge at low temperatures is the manifestation of this zero temperature electron-phonon scattering, we argue that the location of the Urbach focus is the zero temperature unrenormalized gap. Experiments on GaAs yield the zero temperature bare energy gap to be 1.581 eV and thus the renormalization is estimated to be 66 meV.

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Section: Physics Of the Excitonic Urbach Edgesupporting

confidence: 91%

Section: The Urbach Edgementioning

confidence: 99%

Section: Physics Of the Excitonic Urbach Edgementioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

See 2 more Smart Citations

Experimental determination of the bare energy gap of GaAs without the zero-point renormalization

Roy

Mukhuti²,

Bansal³

2019

J. Phys.: Condens. Matter

Self Cite

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“…The difference in the broadenings obtained from the static and the dynamical DFPT schemes is best understood with Eq. (11). Only the electronic states in a narrow energy range are available for scattering.…”

Section: Resultsmentioning

confidence: 99%

Dynamical and anharmonic effects on the electron-phonon coupling and the zero-point renormalization of the electronic structure

Poncé²,

et al. 2015

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The renormalization of the band structure at zero temperature due to electron-phonon coupling is explored in diamond, BN, LiF and MgO crystals. We implement a dynamical scheme to compute the frequency-dependent self-energy and the resulting quasiparticle electronic structure. Our calculations reveal the presence of a satellite band below the Fermi level of LiF and MgO. We show that the renormalization factor (Z), which is neglected in the adiabatic approximation, can reduce the zero-point renormalization (ZPR) by as much as 40%. Anharmonic effects in the renormalized eigenvalues at finite atomic displacements are explored with the frozen-phonon method. We use a non-perturbative expression for the ZPR, going beyond the Allen-Heine-Cardona theory. Our results indicate that high-order electron-phonon coupling terms contribute significantly to the zero-point renormalization for certain materials.PACS numbers: 63.20.kd, 63.20.dk, 71.15.Mb, 71.20.Nr The electron-phonon coupling is at the heart of numerous phenomena such as optical absorption 1,2 , thermoelectric transport 3 , and superconductivity 4-7 . It is also a crucial ingredient in basic electronic structure calculations, giving renormalized quasiparticle energies and lifetimes. This renormalization causes the temperature dependence of the band gap of semiconductors 8 , and accounts for the zero-point renormalization (ZPR), while the lifetime broadenings are observed through the electron mobility 9,10 and in photo-absorption/emission experiments 11 . Obtaining the quasiparticle structure from first principles has been a challenge, addressed for the first time for bulk silicon by King-Smith et al.12 , in 1989, using density functional theory (DFT), with a mixed frozen-phonon supercell and linear response approach. These authors pointed the inadequate convergence of their results with respect to phonon wavevector sampling, due to the limited available computing capabilities. Fifteen year passed, before Capaz et al. computed it for carbon nanotubes 13 using DFT with frozen phonons. At variance with the frozen-phonon approach, the theory of Allen, Heine and Cardona (AHC) [14][15][16] casts the renormalization and the broadening in terms of the first-order derivatives of the effective potential with respect to atomic positions. Used initially with empirical potentials, tight-binding or semi-empirical pseudopotentials 14-20 , AHC was then implemented with the density functional perturbation theory (DFPT) 21-24 , providing an efficient way to compute the phonon band structure and the electron-phonon coupling altogether. This powerful technique allowed A. Marini to compute, from first principles, temperature-dependent optical properties 25 . While DFPT has been widely applied to predict structural and thermodynamical properties of solids 26 , few * gabriel.antonius@gmail.com studies have used it to compute the phonon-induced renormalization of the band structure. The scarcity of experimental data is at least partly responsible for this imbalance. Whereas the phonon s...

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Phonon‐Assisted Electro‐Optical Switches and Logic Gates Based on Semiconductor Nanostructures

Shan

Wang

et al. 2019

Advanced Materials

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High‐performance nanostructured electro‐optical switches and logic gates are highly desirable as essential building blocks in integrated photonics. In contrast to silicon‐based optoelectronic devices, with their inherent indirect optical bandgap, weak light‐modulation mechanism, and sophisticated device configuration, direct‐bandgap‐semiconductor nanostructures with attractive electro‐optical properties are promising candidates for the construction of nanoscale optical switches for on‐chip photonic integrations. However, previously reported semiconductor‐nanostructure optical switches suffer from serious drawbacks such as high drive voltage, limited operation spectral range, and low modulation depth. High‐efficiency electro‐optical switches based on single CdS nanobelts with low drive voltage, ultra‐high on/off ratio, and broad operation wavelength range, properties resulting from unique electric‐field‐dependent phonon‐assisted optical transitions, are demonstrated. Furthermore, functional NOT, NOR, and NAND optical logic gates are demonstrated based on these switches. These switches and optical logic gates represent an important step toward integrated photonic circuits.

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Measurements of the Electric Field of Zero-Point Optical Phonons in GaAs Quantum Wells Support the Urbach Rule for Zero-Temperature Lifetime Broadening

Cited by 18 publications

References 42 publications

Experimental determination of the bare energy gap of GaAs without the zero-point renormalization

Experimental determination of the bare energy gap of GaAs without the zero-point renormalization

Dynamical and anharmonic effects on the electron-phonon coupling and the zero-point renormalization of the electronic structure

Phonon‐Assisted Electro‐Optical Switches and Logic Gates Based on Semiconductor Nanostructures

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