A = area of cross-section

L = length

= resistivity

We know I = JA, J is the current density.

v = drift velocity, = mobility for (n) electrons and (p) holes, respectively and q the electronic charge.

Hence,

Therefore, cut off frequency associated with this device is:

So to increase we must increase

q and are fundamental constants for Si.

If

            So we must increase mobility and therefore drift velocity .

• Increase doping. However, increase in doping reduces mobility & velocity. Therefore optimization needed.

           We need to study the basics of solid state physics to understand about mobility, carrier concentration, etc.