Using a spark gap oscillator in tesla coil designs works relatively well, but it is also very inefficient. As current travels through the air gap, energy is lost in the frictional heating of air inside the gap. The first solution developed to amplify energy transfer was to replace the spark gap with a vacuum tube. A vacuum tube is capable of amplifying electric signals.
Vacuum tubes are basically like the the spark gap only there is no air in the gap, only a vacuum.
This did succeed in minimizing energy losses across the spark gap. However, vacuum tubes are large and bulky contraptions. A smaller more efficient amplifier needed to be developed. This device uses semiconducting, and superconducting materials. The phenomenon of superconductivity is vastly important in technology, because it is very useful to be able to cause change to flow through a super conducting conductor without thermal energy loss.