Re: Why is an ideal semiconductor switching device not achievable in practice?

The reason why an ideal semiconductor, having the characteristics which 
you describe, is not achievable is because of the laws of physics.

For the case, resistance = 0:
Only a superconductor will have zero resistance.  All other conductors 
will have some resistance.  Currently, our superconductor technology 
requires cold temperatures; this is not practical for a semiconductor.

For the case, resistance = infinity:
There are no materials that have an infinite resistance.  Anything can 
conduct electricity if the potential difference is high enough.  
Therefore, there are no perfect insulators

For the case, switching time = 0:
Due to the speed limit imposed by relativity, there will always be some 
non-zero time associated with any two (non-entangled) related events.  If 
you consider a classic, simple switch, then event "B" cannot happen after 
event "A" in a shorter time than it would take a photon to travel the 
distance between "A" and "B".  This time may be very small, but it is not 
zero.