Effects of neutron irradiation on GaAs/AlGaAs heterojunction bipolar transistors

The effects of neutron irradiation on 3-μm-emitter, self-aligned-base, ohmic metal GaAs/AlGaAs heterojunction bipolar transistors and ICs based on molecular beam epitaxy have been experimentally and analytically investigated at fluence levels up to 1.3×10¹⁴ n/cm². Devices with high DC current gain, β, exhibited higher sensitivity to neutron irradiation than those with low β. At 1.3×10¹⁴ n/cm², DC β was degraded by 25% for high-β devices and by 7% for low-β devices. Parasitic base current components such as the emitter edge recombination seem to be the key factor determining the neutron sensitivity. The functional dependence of β on neutron fluence seems to follow the Messenger-Spratt relation, manifested by a linear increase of the base current with fluence. No deterioration was seen either in transistor RF characteristic or in digital circuit high-speed performance due to neutron irradiation up to a fluence of 1.3×10¹⁴ n/cm²