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Fermi-level pinning and charge neutrality level in nitrogen-doped : Characterization and application in phase change memory devices
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Image of FIG. 1.
FIG. 1.

The core-level and VB spectra of samples with nitrogen doping content of (a) 0 at. % and (b) 8.4 at. %. The solid and open symbols represent the core-level spectra for a bulk sample and a sample with a thin metal overlayer, respectively. The VB spectra for bulk sample are shown by solid lines.

Image of FIG. 2.
FIG. 2.

(a) Dependence of hole barrier height on metal work function for undoped . (b) Measured hole barrier as a function of nitrogen doping concentration for the contact between various metals and NGST films. A less negative hole barrier results from an increased nitrogen content in NGST, while a more negative barrier could be achieved by using a metal with a higher work function.

Image of FIG. 3.
FIG. 3.

Plot of vs photon energy for the amorphous samples with atomic nitrogen concentrations from 0% to 8.4%. For each sample, linear extrapolation of the data to the abscissa obtains the band gap. The extrapolation for the undoped is illustrated using a dashed line. The inset shows the band gap as a function of nitrogen concentration.

Image of FIG. 4.
FIG. 4.

The dependence of the real part of the complex dielectric function on wavelength is plotted for films with nitrogen concentrations from 0% to 8.4%.

Image of FIG. 5.
FIG. 5.

Effective work function of Al, W, and Pt vs their vacuum work function on nitrogen content of 0 at. %, 3.5 at. %, 6.2 at. %, 7.7 at. %, and 8.4 at. % in (a), (b), (c), (d), and (e), respectively. The dashed line refers to the metal work functions when there is no Fermi-level pinning of the metals. The intercept between the dashed and straight line denotes the charge neutrality level of the phase change material, represented by a shaded circle in the figures.

Image of FIG. 6.
FIG. 6.

(a) The extracted slope parameter as a function of nitrogen doping concentration in the phase change films. Increasing the nitrogen content does not appear to have a significant impact on the slope parameter of the phase change material. (b) Plot of the slope parameter versus the dielectric constant for a wide range of materials. The solid data points in the plot show how the properties of the phase change materials compares with well-established values of various semiconductor materials (open symbols).

Image of FIG. 7.
FIG. 7.

Schematic energy band diagrams when a metal and phase change material are (a) not in contact and (b) in contact with each other. is almost constant as nitrogen content in the phase change material increases, while it increases with the work function of the overlayer metal.

Image of FIG. 8.
FIG. 8.

The electric dipole contribution between the various metals and as a function of nitrogen doping concentration. The larger difference in electronegativity between NGST and the metal adjacent to the phase change film results in a increase to the electric dipole term.


Generic image for table
Table I.

Effective work function of Al, W, and Pt on the various nitrogen-doped . The vacuum work functions of the respective metals are also shown for comparison.

Generic image for table
Table II.

Various material parameters for nitrogen-doped . The band gap , electron affinity , and charge neutrality level measured with respect to the vacuum level are shown in units of eV. The experimentally extracted slope parameter and the dielectric constant are also recorded.

Generic image for table
Table III.

Theoretical and experimental conduction and VB offsets between and materials such as Si, , , and . The charge neutrality values of the respective materials above the VB edge used in the calculation are also listed.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Fermi-level pinning and charge neutrality level in nitrogen-doped Ge2Sb2Te5: Characterization and application in phase change memory devices