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First-principles calculations on effects of Al and Ga dopants on atomic and electronic structures of amorphous Ge <sub/>2</sub> Sb <sub/>2</sub> Te <sub/>5</sub>
摘要： Effects of post-transition metal dopants M (M = Al, Zn, and Ga) on structural and electronic properties of amorphous Ge2Sb2Te5 (a-GST) are investigated through first-principles calculations based on the density functional theory. The doped a-GST is generated through the melt-quench procedure using molecular dynamics simulations. It is found that the three dopants behave similarly in a-GST, and they are mostly coordinated by Te atoms in tetrahedral geometry, which is similar to those in crystalline MxTey. This is in contrast with crystalline GST wherein the most stable position of dopant M is the octahedral vacancy site. The number of wrong bonds such as Ge–Ge, Ge–Sb, or Sb–Sb increases as dopant atoms predominantly bond with Te atoms. The number of 4-fold ring structures, especially ABAB-type, decreases significantly, explaining the enhanced thermal stability of doped a-GST in the experiment. The bandgap estimated from density of states and the optical gap obtained from Tauc plot increase upon doping, which is also in good agreement with the experiment. By successfully relating the experimental doping effects and changes in the atomic structure, we believe that the present work can serve as a key to offer better retention and lower power consumption in phase-change memory.
关键词： amorphous Ge2Sb2Te5,electronic structures,first-principles calculations,atomic structures,Al and Ga dopants
更新于2025-09-19 17:15:36
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The effect of Ga doping on ZnO thin films subjected to CO2 laser annealing
摘要： The effect of Ga dopant on ZnO thin films was studied for transparent conducting oxide (TCO) applications. In and Ga were selected as dopants for the ZnO thin films, and their mole ratios were varied to identify the optimum proportions of the two dopants. After doping, optical post-annealing processes were applied to improve the conducting properties of the films. By applying optical post-annealing processes, rapid thermal annealing and CO2 laser annealing, the dopants were ionized and thus contributed to the conducting process. The crystal and electrical properties were studied and analyzed. By determining the films’ absorption and transmittance properties, their energy band gaps were calculated, and through X-ray photoelectron spectroscopy analysis, we found that the Ga dopant plays an important role in the TCO behavior. The Ga dopant in the ZnO thin films that had undergone laser annealing improved the electrical conductance properties due to their contributing the oxygen vacancy concentration, increasing the amount of free electrons in the ZnO structure.
关键词： In and Ga dopants,transparent conducting oxides,ZnO
更新于2025-09-16 10:30:52