Try refining the mesh, particularly in critical areas like the junction, and

try using smaller time steps and see if that improves convergence.

. This should help resolve the issue.

i have tried with smaller time steps but there is no improvment and when changing the mess it will take 2-3 hours to run, sometimes after run plots are not accurate

I recommend increasing the mesh size at the junctions and reducing it on the sides as shown in pic in this link https://www.researchgate.net/profile/Dr-Rahi/publication/328900384/figure/fig3/AS:692346719064064@1542079729409/Tony-plot-display-using-2D-mesh-of-double-gate-TFET.png

. Also, ensure doping is considered.