[MatSQ Tip] Module Utilization Tip: How to generate Ge-Sb-Te superlattice - It's Over 9000!


[MatSQ Tip] Module Utilization Tip: How to generate Ge-Sb-Te superlattice

2020-07-29 10:41:12
The generally used computer memory system, SRAM and DRAM, is volatile. The volatile memory needs electric power to store and update the information. However, to use efficiently the state-of-the-arts data science technologies, such as processing big data, we need non-volatile memory technology to enable better performance, the fast data processing speed and high-density storage, with the ultra-low power consumption.

The PCM (phase-change memory) is one of the good candidates for the next-generation nonvolatile memory technologies, due to the low variations of the resistance during lots of read/write cycles.

In particular, the Chalcogenide alloy, Ge-Sb-Te (GST)-based materials, continues to be actively studied due to the ultra-low power consumption characteristics and various suitable characteristics in the PCM field. This outstanding performance of GST originates from a unique data storage mechanism that uses the difference in electrical resistance between the crystalline and amorphous phases. Compared to the conventional crystalline-amorphous phase change, GST has a smaller conformational-entropy difference between the two phases, which can reduce energy consumption during the switching.[1],[2]



In this module tip, we'll learn about how to make the GST superlattice in MatSQ.

 

1. Procedure for generating each model


1. Sb2Te3

1. Search 'Sb2Te3' in 'DATABASE' menu, and select 'mp-1201'.


2. Click the 'CONVENTIONAL' icon at the 'Cell' tab.


3. Save the structure as 'CIF' format and upload that to straighten out the axis.


4. Select unnecessary atoms and press the 'Delete' key to delete them.


5. Move the atoms to the bottom by the 'MOVE' menu of the 'Atoms' tab.
(Subtract as much as z coordinates of the bottom atom)


6. Select 'Cell: Lattice Constant' in the 'EDIT' menu and adjust the length of the z-axis in consideration of PBC.


7. Click the 'Structure list' icon.


8. Change the name of 'Structure-0' into 'Sb2Te3'.


 

2. GeTe

1. Click the '+' button in the 'Structure list' to add a new structure.


2. Change the name of 'Structure-1' into 'GeTe'.


3. Search 'GeTe' in 'DATABASE' menu, and select 'mp-938'.


4. Click the 'CONVENTIONAL' icon at the 'Cell' tab.


5. Save the structure as 'CIF' format and upload that to straighten out the axis.


6. Select unnecessary atoms and press the 'Delete' key to delete them.


7. Move the atoms to the bottom by the 'MOVE' menu of the 'Atoms' tab.
(Subtract as much as z coordinates of the bottom atom)


8. Select 'Cell: Lattice Constant' in the 'EDIT' menu and adjust the length of the z-axis in consideration of PBC.


9. Click 'STRAIN' menu at the 'Cell' tab, and expand the model to fit the lattice constant of Sb2Te3.


 

3. Merge

1. Set like following and click 'Apply' on the 'MERGE' menu of the 'Cell' tab.


Base Structure: Sb2Te3
Attached Structure: GeTe


2. If need, generate supercell on the 'CLONE' menu of the 'Cell' tab.


 

 

2. Appearance setting


1. Open Setting window

1. Click the 'Mouse right button'.


2. Select the 'Display' tab.


 

2. Adjust the atom color

1. Click ▼ button beside the 'Atom'.


2. Click ▼ button of the atom to be color changed.


3. Change the color in the colorbox.


 

3. How to check the model under PBC

1. Click the 'Ghosts' to turn on.


2. 'tol' enables to change the ratio of the ghost atoms. (0~1)


 

4. Adjusting bond

1. Click ▼ button beside the 'Atom'.


2. Click the ▼ button of the atom which to adjust the bond.


3. Adjust the 'Radius' until the bond appears.


4. If the atom size is too large, adjust the total atom size through the 'Atom slider'.


5. Click ▼ button beside the 'Bond'.


6. Uncheck element combinations you don't want to see bonds.


 




[1] Chen, N. K., Li, X. B., Wang, X. P., Xie, S. Y., Tian, W. Q., Zhang, S., & Sun, H. B. (2017). Metal–insulator transition of Ge–Sb–Te superlattice: An electron counting model study. IEEE Transactions on Nanotechnology17(1), 140-146.
[2] Inoue, N., & Nakamura, H. (2019). Structural transition pathway and bipolar switching of the GeTe–Sb2Te3 superlattice as interfacial phase-change memory. Faraday discussions213, 303-319.

 

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