SILVACO ATLAS dielectric

Hi forum,

For simulating a device, the definition of dielectric (or dielectric anisotropy) is very important. Especially if u got vertical or lateral device.
So I got stuck at the definition of the dielectric in ATLAS. The manual says:

ATLAS allows you to specify a value of anisotropic relative dielectric permittivity using the PERM.ANISO parameter on the MATERIAL statement. By default, this is the value of (εyy) if the simulation is in 2D and (εzz) if it is in 3D. The off-diagonal elements are assumed to be zero. In the case of a 3D simulation, you can apply the value of PERM.ANISO to the Y direction instead of the Z direction by specifying YDIR.ANISO or ^ZDIR.ANISO on the MATERIAL statement.

Click to expand...

This means what exactly?
How are the x,y,z axes defined in ATLAS?
εyy or εzz coincides with the c-axis (having in mind the optical axis in a hexagonal crystal '6H-SiC')?
The c-axis is the z-axis of ATLAS? i.e the εzz in the tensor?
Why is εyy the default value for 2D?
What is the Y direction? Again Y direction with respect to what real coordinate system?
These information about how ATLAS is defining the axes for simulation is not included in the manual and cant find any further info o that, so I would appreciate any help on that.

Thank you in advance for reading this, hope you can help me out. If im not clear let me know so i can rephrase some questions. Have a good day :lol: