Abstract:
Electron and neutron irradiation effects in InGaP/GaAs single
heterojunction bipolar transistors are investigated in this thesis. Devices with
different emitter sizes and grown by two different growth techniques were
examined. Based on the physics of heterojunction bipolar transistors and concepts
of radiation damage mechanisms, the irradiation effects were analyzed.
The devices were subjected to electron and neutron irradiation and were
electrically characterized before and after irradiation. Under electron irradiation
these devices were quite robust up to a fluence of 6.69x 10^15 e/cm^2. However, a
more careful analysis showed a slight gain improvement at a low base current and
a small gain degradation at higher base currents. The gain increase at small base
currents and low fluence is believed to be caused by the ionization damage in the
polyimide passivation layer. The gain degradation at higher fluence and high base
currents is due to the displacement damage in the emitter-base junction region.
In the case of neutron irradiation the major effects were (1) the decrease of
collector current or equivalently the common-emitter DC current gain reduction
and (2) the collector-emitter offset voltage shift. At low fluence of neutron
irradiation, a small gain increase is observed at low base currents which is caused
by the suppression of the base current due to ionization effect. At higher fluence,
gain degradation is observed whose magnitude depends upon the nature and
fluence of the irradiation particle. This degradation is caused by the displacement
damage in the SCR leading to the current gain degradation at all base currents. In
addition to the gain degradation, neutron irradiation causes a shift of the collector-emitter
offset voltage, which is caused by the displacement damage in the base-collector
region.
