Dead space effect in space-charge region of collector of AlGaAs/InGaAs p-n-p heterojunction bipolar transistors

Hole-initiated avalanche multiplication is investigated using an AlGaAs/InG aAs p-n-p heterojunction bipolar transistor (HBT). Both experimental measur ements and theoretical calculation are used to determine the avalanche mult iplication factor. A large departure is observed at low electric field when comparison is made between the measured data and theoretical results obtai ned from the standard ionization model. The comparison shows that the conve ntional impact ionization model, based on local electric field, substantial ly overestimates the hole avalanche multiplication factor M-p-1 in the AlGa As/InGaAs p-n-p HBT, where a significant dead space effect occurs in the co llector space-charge region. A simple correction model for the dead space i s proposed, that allows the multiplication to be accurately predicted, even in a heavily doped structure. Based on this model, multiplication characte ristics for different threshold energy of the hole are calculated. A thresh old energy of 2.5 eV was determined to be suitable for describing the hole- initiated impact ionization process. (C) 2001 American Institute of Physics .