Q. The material used to fabricate IMPATT diodes is GaAs since they have the highest efficiency in all aspects.

 impatt diodes can be fabricated using silicon, germanium, gaas or indium phosphide. out of these materials, gaas have highest efficiency, low noise and high operating frequencies. but gaas has a major disadvantage of complex fabrication process and higher cost. so, gaas are not preferred over silicon and germanium.