Semiconductor device and equipment for communication system

Equipment for a communication system handling an RF signal, the equipment being disposed in the communication system and having an active element formed by using a semiconductor, the active element comprising:

• at least one first active region disposed on a substrate and composed of a first semiconductor;
• and
• at least one second active region disposed in contact with the first active region and composed of a second semiconductor having a band gap different from a band gap of the first semiconductor such that a band discontinuity occurs between the first and second active regions, the second active region being composed of:
• at least one first semiconductor layer which allows passage of carriers therethrough;
• and
• at least one second semiconductor layer containing an impurity for carriers at a concentration higher than in the first semiconductor layer and smaller in film thickness than the first semiconductor layer such that carriers spread out to the first semiconductor layer under a quantum effect,
• the first and second semiconductor layers being disposed in contact with each other.