Ultrafast amorphization in Ge_10Sb_2Te_13 thin film induced by single femtosecond laser pulse

Konishi, M.; Santo, Hisashi; Hongo, Yuki; Tajima, Kazuyuki; Hosoi, Masaharu; Saiki, Takanao

doi:10.1364/ao.49.003470

Cited by 65 publications

(43 citation statements)

References 11 publications

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“…Non-thermal effects may be present; particularly nonthermal melting and amorphization under femtosecond laser excitation. 34,37 Confirmation of their influence would require transient reflectivity and structural measurements which will form the scope of future investigations.…”

Section: Discussionmentioning

confidence: 99%

Crystallization of Ge2Sb2Te5 films by amplified femtosecond optical pulses

Liu

Aziz

Shalini

et al. 2012

Journal of Applied Physics

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The phase transition between the amorphous and crystalline states of Ge 2 Sb 2 Te 5 has been studied by exposure of thin films to series of 60 femtosecond (fs) amplified laser pulses. The analysis of microscope images of marks of tens of microns in size provide an opportunity to examine the effect of a continuous range of optical fluence. For a fixed number of pulses, the dependence of the area of the crystalline mark upon the fluence is well described by simple algebraic results that provide strong evidence that thermal transport within the sample is one-dimensional (vertical). The crystalline mark area was thus defined by the incident fs laser beam profile rather than by lateral heat diffusion, with a sharp transition between the crystalline and amorphous materials as confirmed from line scans of the microscope images. A simplified, one-dimensional model that accounts for optical absorption, thermal transport and thermally activated crystallization provides values of the optical reflectivity and mark area that are in very good quantitative agreement with the experimental data, further justifying the one-dimensional heat flow assumption. Typically, for fluences below the damage threshold, the crystalline mark has annular shape, with the fluence at the centre of the irradiated mark being sufficient to induce melting. The fluence at the centre of the mark was correlated with the melt depth from the thermal model to correctly predict the observed melt fluence thresholds and to explain the closure and persistence of the annular crystalline marks as functions of laser fluence and pulse number. A solid elliptical mark may be obtained for smaller fluences. The analysis of marks made by amplified fs pulses present a new and effective means of observing the crystallization dynamics of phase-change material at elevated temperatures near the melting point, which provided estimates of the growth velocity in the range 7-9 m/s. Furthermore, finer control over the crystallization process in phase-change media can be obtained by controlling the number of pulses which, along with the laser fluence, can be tailored to any medium stack with relaxed restrictions on the thermal properties of the layers in the stack. V C 2012 American Institute of Physics. [http://dx

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Section: Discussionmentioning

confidence: 99%

Crystallization of Ge2Sb2Te5 films by amplified femtosecond optical pulses

Liu

Aziz

Shalini

et al. 2012

Journal of Applied Physics

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“…An amorphous-to-crystalline phase transition is induced by irradiating the alloy using focused nanosecond laser pulses or continuous-wave laser output via transient temperature ramping, 3 whereas a crystalline-to-amorphous phase transition can be driven by femtosecond laser pulses via a non-thermal process. 4 Although there have been many attempts to reveal the mechanism of the phase transitions in phase change chalcogenide alloys, 4-7 the rapid crystalline-to-amorphous phase transition is not fully understood because the amorphization occurs as a single-shot event that is completed on a femtosecond time scale. Therefore, to understand the dynamics of this ultrafast amorphization, single-shot detection of the amorphization process with femtosecond time resolution is essential.…”

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confidence: 99%

Ultrafast crystalline-to-amorphous phase transition in Ge2Sb2Te5 chalcogenide alloy thin film using single-shot imaging spectroscopy

Takeda

Oba

Minami

et al. 2014

Applied Physics Letters

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We have observed an irreversible ultrafast crystalline-to-amorphous phase transition in Ge2Sb2Te5 chalcogenide alloy thin film using broadband single-shot imaging spectroscopy. The absorbance change that accompanied the ultrafast amorphization was measured via single-shot detection even for laser fluences above the critical value, where a permanent amorphized mark was formed. The observed rise time to reach the amorphization was found to be ∼130–200 fs, which was in good agreement with the half period of the A1 phonon frequency in the octahedral GeTe6 structure. This result strongly suggests that the ultrafast amorphization can be attributed to the rearrangement of Ge atoms from an octahedral structure to a tetrahedral structure. Finally, based on the dependence of the absorbance change on the laser fluence, the stability of the photoinduced amorphous phase is discussed.

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“…We used a thicker film compared to previous samples (Figs. [2][3][4][5] in order to observe the evolution of morphology more clearly. SEM images captured at 100, 140, 145, and 150 • C in a single heating run are shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…The structural, optical, thermal, and electrical properties of bulks and thin-films of chalcogenides are still the subjects of intensive research [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Recently, the size of memory cells for phase change memory (PCM) has been driven down further and further in order to reduce power consumption.…”

Section: Introductionmentioning

confidence: 99%