Energetic electron-induced impurity ionization in Si:As IBC detectors

The problem of persistent dose rate gamma noise in impurity-band-conduction (IBC) silicon infrared detectors was investigated using a novel experimental approach. Of interest is the possibility that energetic electrons from gamma events create impurity band carriers as well as intrinsic carriers. If collected, these carriers would comprise a significant component of the gamma pulse amplitudes. To test this, an experiment was conducted to determine the ratio of impurity-band holes to valence-band holes collected in response to incident energetic electrons, such as those resulting from a gamma event. An upper limit of 10% was found for this ratio. The transient response was measured for pulses of both 20-μm IR and energetic electron (13 keV and 39 keV) irradiation, and the much longer transit time of impurity-band holes relative to that of valence-band holes and electrons was used to distinguish their contribution to the current. A first-order model for the transient response was derived that predicted contributions from RC time constant (dielectric relaxation time) effects in the undepleted region of the detector as well as from transit time (drift) effects in the depleted region, and allowed the deconvolution of the two contributions