Changes in the electronic structures and optical band gap of Ge2Sb2Te5 and N-doped Ge2Sb2Te5 during phase transition

Abstract

Changes in the electronic structures of Ge2Sb2Te5 (GST) and N-doped Ge2Sb2Te5 film during the phase transition from an amorphous to a crystalline phase were studied using synchrotron radiation high-resolution x-ray photoemission spectroscopy. The changes in tetrahedral and octahedral coordinated Ge 3d peaks are closely related to the changes in the chemical bonding state of GST films. The metallic Sb peak in the Sb 4d spectra of annealed GST films demonstrates that the metallic Sb atoms become segregated during thermal treatment resulting in phase separation. The incorporation of nitrogen into the GST film affects its structure and chemical bonding state, resulting in the suppression of crystallization. The incorporation of nitrogen also increases the optical band gap of the film due to the formation of a nitride.

Hard x-ray photoelectron spectroscopy study of Ge2Sb2Te5; as-deposited amorphous, crystalline, and laser-reamorphized

“…The finding of a second germanium species at higher coordination constituting of 36% of the total spectra in the crystalline phase agrees well with the theoretical prediction of 30% presence of nonresonant bonds in Ge 2 Sb 2 Te 5 , 10 and it is conceivable that it is this very small relative change in bonding that is the underlying foundation of the very fast phase change in Ge 2 Sb 2 Te 5 . While the trend of shift from octahedrally to tetrahedrally coordinated germanium agrees with the work of Kim et al, 17 in our work, unlike the cited study, the majority of the change of the spectral shape stems not from a transfer of intensity from one species to another but much more from a broadening of the constituent signals, i.e., the full width at half maximum (FWHM) of the fitted peaks is much larger for the amorphous samples compared to the crystalline one leading to much stronger overlap of spectral features in the amorphous cases.…”

Temperature dependence of thermal properties of Ag8In14Sb55Te23 phase-change memory materials

“…When the laser beam is switched off, the melted marks quench into an amorphous state due to the high thermal conductivity of the substrate underneath the phase-change materials. Conversely, the recorded marks are erased when the materials are heated above the glass transition temperature but yet below the melting threshold so that the materials return to the crystalline state [7][8][9][10][11][12][13][14][15][16][17]. For the nonvolatile electrical storage, applying a higher voltage pulse (reset pulse) to the crystalline state with low resistivity leads to the local melting and consequently the formation of an amorphous information bit with high resistivity due to the rapid quenching.…”

“…With the development of the phase-change memory, various materials were examined, and the materials of the best performances in terms of speed and stability were found to be GeSbTe (abbreviated as GST) family, such as Ge 2 Sb 2 Te 5 and Ge 1 Sb 4 Te 7 [4,9,16,17,[21][22][23], and AgInSbTe (abbreviated as AIST) family, such as Ag 3.4 [2,3,7,[11][12][13][14][15][24][25][26][27][28]. The thermal properties of GST family were measured and studied in details, and the studies showed that there were common characteristics for different members in the GST family due to the distorted NaCl-type rock structures [21,22].…”

“…Chalcongenide phase-change materials are extensively used as the optical and nonvolatile electrical data storage media due to the apparent difference in optical reflectivity and electrical resistivity between the crystalline and amorphous state [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. For optical data storage, the recording is achieved by forming amorphous marks on a crystalline base with a focused laser beam.…”

Thermal Stability of SiO2Doped Ge2Sb2Te5for Application in Phase Change Random Access Memory

“…[3,4] However, the high level of reset current (I res ) has been a major obstacle to the further scaling of PCRAM, because of the limited on-current drive capability of the cell transistor (< 0.5 mA/μm). There have been various investigations on the improvement of the switching performance of GST [5][6][7][8][9][10][11][12]. Although many improvements have been made in reducing I res , there still remain several issues to be resolved and one of them is the device reliability during the repeated switching cycles; degradation or failure of PCRAM devices, such as reset and set stuck, and compositional variation of phase change material, have been reported [13][14][15][16].…”