Phase transition in stoichiometric GaSb thin films: Anomalous density change and phase segregation

Putero, Magali; Coulet, Marie‐Vanessa; Ouled-Khachroum, T.; Müller, Christophe; Baehtz, Carsten; Raoux, Simone

doi:10.1063/1.4842175

Cited by 24 publications

(20 citation statements)

References 22 publications

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“…For the octahedral configuration, we used single scattering paths given by three Ge-Te bonds at 2.80 Å and another three Ge-Te bonds at 3.15 Å . 64 The presence of homopolar Te-Te bonds was reported earlier by EXAFS analysis on GeTe crystalized thin films, 60 but they were not considered in our analysis. An amplitude reduction factor of 0.76 was kept fixed for all simulations at all temperatures.…”

Section: Gete/gasbmentioning

confidence: 90%

“…After GeTe crystallization, we consider that some of the Ga atoms (which are the smallest atoms in the structure) diffused in the vacancies of the GeTe crystalline structure (the GeTe crystalline structure contains up to 10% vacancies). Diffusion produced an increased concentration of Sb in the GaSb film which will lead to a reduction of the crystallization temperature as shown by Raoux et al 60 The crystallization temperature is composition dependent, decreasing with the increase in Sb concentration. Thus, the crystallization temperature of the Sb-rich GaSb layer is decreased to 168 C. On the other hand, the interface might play a role in the crystallization of GaSb.…”

Section: Gete/gasbmentioning

confidence: 93%

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In-situ crystallization of GeTe\GaSb phase change memory stacked films

Velea

Borca

Socol

et al. 2014

Journal of Applied Physics

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Single and double layer phase change memory structures based on GeTe and GaSb thin films were deposited by pulsed laser deposition (PLD). Their crystallization behavior was studied using in-situ synchrotron techniques. Electrical resistance vs. temperature investigations, using the four points probe method, showed transition temperatures of 138 C and 198 C for GeTe and GaSb single films, respectively. It was found that after GeTe crystallization in the stacked films, Ga atoms from the GaSb layer diffused in the vacancies of the GeTe crystalline structure. Therefore, the crystallization temperature of the Sb-rich GaSb layer is decreased by more than 30 C. Furthermore, at 210 C, the antimony excess from GaSb films crystallizes as a secondary phase. At higher annealing temperatures, the crystalline Sb phase increased on the expense of GaSb crystalline phase which was reduced. Extended X-ray absorption fine structure (EXAFS) measurements at the Ga and Ge K-edges revealed changes in their local atomic environments as a function of the annealing temperature. Simulations unveil a tetrahedral configuration in the amorphous state and octahedral configuration in the crystalline state for Ge atoms, while Ga is four-fold coordinated in both as-deposited and annealed samples. V

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Section: Gete/gasbmentioning

confidence: 90%

Section: Gete/gasbmentioning

confidence: 93%

In-situ crystallization of GeTe\GaSb phase change memory stacked films

Velea

Borca

Socol

et al. 2014

Journal of Applied Physics

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“…At the respective crystallization temperature which can be deduced from the left side of Fig. 2, however, for the Ga:Sb = 45:55 alloy the Kiessig fringes shift abruptly to lower angles (as expected for this alloy because of the decrease in mass density and related increase in film thickness 13 ), for the Ga:Sb = 30:70 alloy the Kiessig fringes period do not shift at all, and for the Ga:Sb = 9:91 alloy the Kiessig fringes shift abruptly to high angles indicating an increase in mass density and a reduction in film thickness. The dashed lines are a guide to the eye for the shift direction.…”

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confidence: 99%

“…These materials include Cu 2 GeTe 3 , 6, 10 Fe-Te, 11 Ge-rich Ge-Sb compositions, 12 and GaSb. 13 In order to optimize phase change materials for PCRAM application, we have studied systematically Ga-Sb alloys by adding Sb (positive mass density change) to GaSb (negative mass density change). Combined in situ synchrotron X-ray diffraction (XRD), X-ray reflectivity (XRR), and sheet resistance (Rs) measurements reveal the interesting crystallization behavior of these alloys.…”

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confidence: 99%

Unusual crystallization behavior in Ga-Sb phase change alloys

et al. 2013

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Combined in situ X-ray scattering techniques using synchrotron radiation were applied to investigate the crystallization behavior of Sb-rich Ga-Sb alloys. Measurements of the sheet resistance during heating indicated a reduced crystallization temperature with increased Sb content, which was confirmed by in situ X-ray diffraction. The electrical contrast increased with increasing Sb content and the resistivities in both the amorphous and crystalline phases decreased. It was found that by tuning the composition between Ga:Sb = 9:91 (in at.%) and Ga:Sb = 45:55, the change in mass density upon crystallization changes from an increase in mass density which is typical for most phase change materials to a decrease in mass density. At the composition of Ga:Sb = 30:70, no mass density change is observed which should be very beneficial for phase change random access memory (PCRAM) applications where a change in mass density during cycling is assumed to cause void formation and PCRAM device failure.

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“…It is expected that, as the atomic density, and hence the electron density, increases, so does the refractive index, and hence also the reflectivity, which is one explanation for this anomalous behaviour. A very few other PCM materials also exhibit an anomalous negative density change on the a-c phase transition; these include GaSb [17,18], Fe-Te [9] and Ge-rich Ge-Sb materials [19].…”

Section: Gecu 2 Tementioning

confidence: 99%

Ab Initio Molecular-Dynamics Simulations of Doped Phase-Change Materials

Skelton

Lee

Elliott

2015

Molecular Dynamics Simulations of Disordered Materials

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The physical behaviour and device performance of phase-change, non-volatile memory materials can often be improved by the incorporation of small amounts of dopant atoms. In certain cases, new functionality can also be introduced, for example a contrast in magnetic properties between amorphous and crystalline phases of the host phase-change material when certain transition-metal dopants are included. This Chapter reviews some of the experimental data relating to doped phase-change materials and, in particular, a survey is given of the role played by molecular-dynamics simulations in understanding the atomistic mechanisms involved in the doping process. In addition, some examples are given of the in silico discovery of new phase-change compositions resulting from ab initio molecular-dynamics (AIMD) simulations.

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Phase transition in stoichiometric GaSb thin films: Anomalous density change and phase segregation

Cited by 24 publications

References 22 publications

In-situ crystallization of GeTe\GaSb phase change memory stacked films

In-situ crystallization of GeTe\GaSb phase change memory stacked films

Unusual crystallization behavior in Ga-Sb phase change alloys

Ab Initio Molecular-Dynamics Simulations of Doped Phase-Change Materials

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