Avalanche multiplication in GaInP/GaAs single heterojunction bipolar transistors

The electron multiplication factors in GaInP/GaAs single heterojunction bipolar transistors (HBT´s) have been measured as a function of base-collector bias for a range of GaAs collector doping densities. In the lowest doped (5×10¹⁴ cm^-3) thick collector the multiplication is determined by the local electric field. As the collector doping increases, the measured multiplication is found to be significantly reduced at low values of multiplication from that predicted by the electric field profile. However, good agreement is always found at high multiplication, close to breakdown. This reduction in multiplication at low electric fields is attributed to the dead space, the minimum distance over which carriers must travel before gaining the ionization threshold energy. A simple correction for the dead space is proposed, allowing the multiplication to be accurately predicted even in heavily doped structures