Sir, thank you for your comment

The structure do take my fabricated device into account,Both we know the PD bandwidth is depended on the charge transport time and the electrical response. So this is why I want to get the travel time .

I really want your suggestion about how to get it in approximate way.

In order to get the travel time ,I had tried the 2D-x normal steady simulation. but there is another error.

Here is my simulation log.

Error (divergence): Drift-diffusion/Poisson solver failed to converge after 10000 iterations, 0.376543(1e-007) remains. Residual (ratio/last) 1.81525e+006/35547.3.

Warning: the charge transport solver failed to converge. A partial result will be saved.

The program terminated due to an error: The simulated result is incomplete. Please review the log files for details.

Error: there was an unknown parallel error. The error code is 9002, the process number is 0

How do I make this right? Thank you very much!