Design of AlGaN/GaN Heterojunction Bipolar Transistor Structures

The potential of III-nitride materials for the fabrication of bipolar transistors is investigated theoretically. Several different pseudomorphic AlGaN/GaN n-p-n heterojunction bipolar transistor structures are examined through calculations of their band profiles and majority carrier distributions in equilibrium. Spontaneous and piezoelectric polarization charges are utilized to create large hole sheet carrier densities in the base layer, thus minimizing the base spreading resistance. At the same time, a large accelerating field in the base can help reduce the base transit times of the electrons and, hence, increase the current gains of these devices. The effect of strain due to substrate mismatch is also investigated.