Rise time and fall time

what is turn on time and off time of epc2001 and epc2107. i want to switch 100v by 1ns pulse. please suggest GaN for it.

the switching times will depend on your topology and circuit design. To get an idea of a typical behavior, you can take a look at the half-bridge demo boards of the devices.
By the way, the EPC2001 is obsolete, there is a newer version EPC2001c. Both of the EPC2001c and EPC2107 are previous generations, and although plenty fast, some newer devices might provide better price/performance based on your application. You can use our GaN FET Selection Tool for Buck Converters (epc-co.com) to screen for parts based on some representative conditions for you.
In general, I recommend you take a look at each step shown here: GaN Design Support Center for EPC Products | EPC (epc-co.com).
Once you have the right device (Step 2) and gate driver (Step 3), you can check switching times using LTSpice (step 5.2).