Optimized profiles for neutron and photocurrent hardened power transistors

This paper discusses two problems: the partitioning of bipolar transistor breakdown voltage between the collector and the base in the context of neutron tolerance, and the dependence of collector photocurrent on substrate doping. It is suggested that enhanced neutron tolerance for a given breakdown voltage may sometimes be achieved by increasing the basewidth so that a portion of the breakdown voltage is supported by the base. Peak current gains of ten were achieved with a four micron basewidth after exposure to 3 &time; 10¹⁴ neutrons (1 MeV eq.) cm⁻². Substrate photocurrents were found to be very dependent on substrate doping; by using a substrate doping of 10²⁰ cm⁻³, substrate photo-currents were suppressed to an equivalent silicon photocurrent collection length of three microns.