Hi. The “overflow” error arises when the solver diverges. The results (numbers) become too large to save and overflow occurs. To solver this problem we have to figure out why the solver is diverging. Most often the reason is some error in the simulation setup.
When I looked at your file and calculated the mesh, I noticed that the top of the circle was not getting doped. Your import doping object for the circle was 0.5 um long whereas the circle itself was 0.6 um long. This means that the surface in contact with the metal was low-doped. This would create problem with convergence. I have reduced the height of the top circle to match the extent of the doping object. I have also made the inner radius of the emitter contact larger so that it just contacts the outside of the circle and does not cut it out. Finally, I noticed that the P+ doping object was extended so that it was covering not only the substrate but also the cone and the top circle. I have shrunk it so that it now only covers the substrate. The doping profile now looks reasonable.
When I run the file now the solver is able to simulate it properly without any error. Below is the I-V I am getting with the above mentioned changes.
I am attaching the modified file here (final_mod.ldev (6.4 MB)). Note that I had to remove the import doping and generation object to make the file smaller. You will have to place them in the file again. Please let me know if you have any problem running the file.