Ultrafast defect dynamics: A new approach to all optical broadband switching employing amorphous selenium thin films

Sharma, Rituraj; Prasai, K.; Drabold, D. A.; Adarsh, K. V.

doi:10.1063/1.4927543

Cited by 6 publications

(5 citation statements)

References 37 publications

(33 reference statements)

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“…We make use of a 216-atom model of Zhang and Drabold [31] and relax it using LDA in a plane wave basis. The model represents the material reasonably well as reported in earlier work [31,43]. It is notable from figure 2 that the DOS is higher near the Fermi level for a-Se.…”

Section: Amorphous Seleniumsupporting

confidence: 80%

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Electrons and phonons in amorphous semiconductors

Prasai

Biswas

Drabold

2016

Semicond. Sci. Technol.

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The coupling between lattice vibrations and electrons is one of the central concepts of condensed matter physics. The subject has been deeply studied for crystalline materials, but far less so for amorphous and glassy materials, which are among the most important for applications. In this paper, we explore the electron-lattice coupling using current tools of a first-principles computer simulation. We choose three materials to illustrate the phenomena: amorphous silicon (a-Si), amorphous selenium (a-Se) and amorphous gallium nitride (a-GaN). In each case, we show that there is a strong correlation between the localization of electron states and the magnitude of thermally induced fluctuations in energy eigenvalues obtained from the density-functional theory (i.e. Kohn-Sham eigenvalues). We provide a heuristic theory to explain these observations. The case of a-GaN, a topologically disordered partly ionic insulator, is distinctive compared to the covalent amorphous examples. Next, we explore the consequences of changing the charge state of a system as a proxy for tracking photoinduced structural changes in the materials. Where transport is concerned, we lend insight into the Meyer-Neldel compensation rule and discuss a thermally averaged Kubo-Greenwood formula as a means to estimate electrical conductivity and especially its temperature dependence. We close by showing how the optical gap of an amorphous semiconductor can be computationally engineered with the judicious use of Hellmann-Feynman forces (associated with a few defect states) using molecular dynamics simulations. These forces can be used to close or open an optical gap, and identify a structure with a prescribed gap. We use the approach with plane-wave density functional methods to identify a low-energy amorphous phase of silicon including several coordination defects, yet with a gap close to that of good quality a-Si models.

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Section: Amorphous Seleniumsupporting

confidence: 80%

“…The timescale associated with this relaxation from occupation-induced changes are short (e.g. a few phonon periods), which can be exploited to develop novel applications in solids involving ultrafast processes [43]. This approach was pioneered by Peter Fedders and coworkers [44].…”

Section: Structural Change From Electronic/optical Modificationmentioning

confidence: 99%

Electrons and phonons in amorphous semiconductors

Prasai

Biswas

Drabold

2016

Semicond. Sci. Technol.

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“…Iex and I0 are the transmitted intensities of the sequential probe pulses after a delay time τ following excitation by the pump beam and in the ground state respectively [18,20]. It is important to note that all the pump-probe measurements are performed in ambient condition.…”

Section: Methodsmentioning

confidence: 99%

“…In the former theme, bandgap light illumination produces electron-hole states known as excitons that get self-trapped in the deformable glassy network. The self-trapping of excitons can be attributed to the formation of metastable local defect configurations of under-and overcoordinated chalcogen atoms in the neutral and charged states [17][18][19][20]. These local structural changes form localized states in the tail of the band edges and results in a reduction of the bandgap.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast light-induced softening of chalcogenide thin films above the rigidity percolation transition

Khan

Yadav

Adarsh

2018

Journal of Applied Physics

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Little is known about the role of network rigidity in light-induced structural rearrangements in network glasses due to a lack of supporting experiments and theories. In this article, we demonstrate for the first time the ultrafast structural rearrangements manifested as induced absorption (IA) over a broad spectral range in a-GexAs35-xSe65 thin films above the mean-field rigidity percolation transition, quantified by the mean coordination number ⟨r⟩ = 2.40. The IA spectrum arising from self-trapped excitons, induced structural rearrangements by softening the glass network that strikingly reveal two relaxation mechanisms which differ by one order of magnitude. The fast kinetics of electron-lattice interaction occurs within 1 ps, exhibits a weak dependence on rigidity and dominates in the sub-bandgap region. In a stark contrast, the slow kinetics are associated with the structural changes in the bandgap region and depends strongly on network rigidity. Our results further demonstrate that amplitude of IA scales a linear relationship with excitation fluence which provides a unique way to induce structural rearrangements in over-coordinated network to exploit it for practical purposes. Our results modify the conventional concept of rigidity dependence of light-induced effects in network glasses, when excited with an ultrafast laser.

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“…21) Then, we may again adopt the transient absorption. 30,31,36) Although quantitative evaluations are difficult, it may give ΔT ≈ 10 1 -10 2 K. Since the thermal expansion coefficients of these glasses are ∼3 × 10 −5 K −1 , 27,37) the transient temperature rise possibly causes explosive volume expansion (in super-cooled states in Se), which may result in the crater-like damages. It is interesting to note that such thermal damage does not induce crystallization in Se, in contrast to the fs pulse effect.…”

mentioning

confidence: 99%

Femto- and nano-second laser-induced damages in chalcogenide glasses

Li¹,

Qi²,

Wang³

et al. 2019

Jpn. J. Appl. Phys.

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We have studied damaging behaviors in bulk As2Se3, Se and As2S3 glasses using fs and ns laser pulses. Threshold fluence of laser damages markedly varies with excitations and materials. Under sub-gap fs pulses with photon-energy of ħω = 1.6 eV, the threshold in As2S3 is roughly twice that of the other two glasses, and photo-crystallization appears in Se. For ns pulses, all the glasses under bandgap (ħω = 2.3 eV) illumination possess higher thresholds than those under mid-gap (ħω = 1.2 eV) illumination. These observations are discussed, taking electronic and thermal effects into account.

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Ultrafast defect dynamics: A new approach to all optical broadband switching employing amorphous selenium thin films

Cited by 6 publications

References 37 publications

Electrons and phonons in amorphous semiconductors

Electrons and phonons in amorphous semiconductors

Ultrafast light-induced softening of chalcogenide thin films above the rigidity percolation transition

Femto- and nano-second laser-induced damages in chalcogenide glasses

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