Electronic structure of intrinsic defects in crystalline germanium telluride

Edwards, Arthur H.; Pineda, Andrew C.; Schultz, Peter A.; Martin, Marcus G.; Thompson, Aidan P.; Hjalmarson, Harold P.; Umrigar, C. J.

doi:10.1103/physrevb.73.045210

Cited by 222 publications

(199 citation statements)

References 33 publications

(22 reference statements)

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“…Therefore, there are three delocalized holes on the top of the valence band. These results are in agreement with previous LDA calculations [41]. We now consider the point defects in s-GeSb2Te4.…”

Section: Resultssupporting

confidence: 92%

“…Note that o-GeTe is proposed as a lower symmetry crystalline approximation to the real amorphous GeTe and its sX band gap coincides with the experimental value. Theoretically, the calculated band gap values of r-GeTe varied from 0.367 eV to 0.66 eV based on the LDA functional [23,37,41], quantum mote carlo method gave even larger value of 0.7 eV [41]. Previous relativistic band structure calculations showed smaller band gap values, assuming the GeTe in the fcc structure [42,43].…”

Section: Resultsmentioning

confidence: 88%

“…It can be viewed as the interplay between elemental TM atom and Ge or Sb vacancy. It is well known that excessive vacancies are presented in GST, which are speculated to be related to the ptype conductivity, switching mechanism, high crystallization speed, metal-insulator transitions in crystalline GST [45,46 and [41,47]. Therefore, we only consider TM atom on Ge or Sb site in this work.…”

Section: Resultsmentioning

confidence: 99%

“…3 the LDOSs of single neutral Ge and Sb vacancy, respectively, in r-GeSb2Te4 (r-GeTe similarly). Edwards et al [41] found that the geometry relaxation around the single vacancy in r-GeTe is small. We use the unrelaxed vacancy configurations here.…”

Section: Resultsmentioning

confidence: 99%

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Electronic Structure and Spin Configuration Trends of Single Transition Metal Impurity in Phase Change Material

Hong

Pei

Shi

2016

Journal of Elec Materi

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Fe doped GST has shown experimentally the ability to alter its magnetic properties by phase change. In this work, we use screened exchange hybrid functional to study the single neutral substitutional 3d transition metal (TM) in crystalline GeTe and GeSb2Te4. By curing the problem of local density functional (LDA) such as over delocalization of the 3d states, we find that Fe on Ge/Sb site has its majority d states fully occupied while its minority d states are empty, which is different than previous predicted electronic configuration by LDA. From early transition metal Cr to heavier Ni, the majority 3d states are gradually populated until fully occupied and then the minority 3d states begin to be filled. In order to study the magnetic contrast, we use lower symmetry crystalline GeTe and GeSb2Te4 as the amorphous phases, respectively, which has been proposed to model the medium range disordering. We find that only Co substitution in r-GeSb2Te4 and s-GeSb2Te4 shows magnetic contrast. The experimental magnetic contrast for Fe doped GST may be due to additional TM-TM interaction, which is not included in our model. It can also be possible that these lower symmetry crystalline models are not sufficient to characterize the magnetic properties of real 3d TM doped amorphous GST.

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Section: Resultssupporting

confidence: 92%

Section: Resultsmentioning

confidence: 88%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Electronic Structure and Spin Configuration Trends of Single Transition Metal Impurity in Phase Change Material

Hong

Pei

Shi

2016

Journal of Elec Materi

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“…37 This is a common situation in DF calculations, and spin-orbit corrections further reduce the gap in c-GeTe. 38 Amorphization in semiconductors usually results in broader valence and conduction bands that can overlap, so a larger band gap is unusual. 10 The overall form of the DOS ͑Fig.…”

Section: E Electronic Structurementioning

confidence: 99%

Structural phase transitions on the nanoscale: The crucial pattern in the phase-change materialsGe2Sb2Te5and GeTe

2007

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Phase-change materials are of immense importance for optical recording and computer memory, but the structure of the amorphous phases and the nature of the phase transition in the nanoscale bits pose continuing challenges. Massively parallel density functional simulations have been used to characterize the amorphous structure of the prototype materials Ge 2 Sb 2 Te 5 and GeTe. In both, there is long-ranged order among Te atoms and the crucial structural motif is a four-membered ring with alternating atoms of types A ͑Ge and Sb͒ and B ͑Te͒, an "ABAB square." The rapid amorphous-to-crystalline phase change is a reorientation of disordered ABAB squares to form an ordered lattice. There are deviations from the "8 − N rule" for coordination numbers, with Te having near threefold coordination. Ge atoms are predominantly fourfold coordinated, but-contrary to recent speculation-tetrahedral coordination is found in only approximately one-third of the Ge atoms. The average coordination number of Sb atoms is 3.7, and the local environment of Ge and Sb is usually "distorted octahedral" with AB separations from 3.2 to 4 Å in the first coordination shell. The number of A -A bonds is significantly greater in GeTe than in Ge 2 Sb 2 Te 5 . Vacancies ͑voids͒ in the disordered phases of these materials provide the necessary space for the phase transitions to take place. The vacancy concentration in Ge 2 Sb 2 Te 5 ͑11.8%͒ is greater than in GeTe ͑6.4%͒, which is consistent with the better phase-change performance of the former.

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