I am interested in the possibility of using a combination of FDTD and DEVICE (charge and heat) to simulate thermionic emission across a vacuum gap. Is this possible?

Furthermore, I have read that quantum tunneling cannot be simulated by Lumerical. What is the smallest gap distance charge can model before quantum effects take place? 10x the electron wavelength?

# FDTD, DEVICE modeling of vacuum gap thermionic emission

**devon.jensen**#1

**aalam**#2

Hi @devon.jensen, my apologies for the long delay in getting a response. Since you are talking about both charge and heat I am assuming you want to use charge to model some sort of electrical transport and calculate the amount of Joule heating and then use heat to model the heat transport? If that is what you want to do then it is possible to run the charge and heat solvers in a coupled mode to get the complete electro-thermal picture. Unfortunately you wonâ€™t be able to model thermionic emission across a vacuum gap using the heat solver. The raditation boundary condition in the heat solver only works to model heat loss to open space. It does not model radiation from one surface to another.

Regarding the second question, the charge solver will simulate a structure with any length of gap. The only thing is that the current through the gap will always be zero irrespective of the width of the gap (since the solver cannot calculate tunneling). I am not sure at what gap current starts to flow through vacuum though. However I am sure there are enough articles out there that discusses this.