Measurement of the electron ionization coefficient at low electric fields in Heterojunction Bipolar Transistors

摘要

New data for the electron impact-ionization coefficient α_n in GaAs and In_(0.53)Ga_(0.47)As are derived from measurements of the multiplication coefficient M-1 in Heterojunction Bipolar Transistors (HBT). We show that the intrinsic limiting factors of the M-1 measurement at low electric fields are the Early effect and the uncertainty in the electric field value in the collector depletion region. By adopting HBT's characterized by lightly doped collectors and heavily doped base regions we were able to extend previously available data on the impact-ionization coefficient of GaAs and In_(0.53)Ga_(0.47)As by two orders of magnitude, down to α_n = 1 cm~(-1). Our data on In_(0.53)Ga_(0.47)As also confirm the theoretical results on the weak field dependence of α_n at low electric fields.