You can simulate and plot band to bant tunneling rate vs device length but only one by and you get different results, finaly you can use origin to plot this results in the same figure.
For example in ATLAS or DevEdit you make your 3D devices with a lenght taht you choose and you get your devices in Tonyplot3D.and in Tonyplot 3D there are a possibility to cut plane your device and you obtained a 2D of your devices and with this and cutline you can have your band to band tunneling and export this results.
and repeat another 3D devices with different length and repeat all this step and go to Origin and assemble yours results in the same figure.