Electrical and Computer Engineering ETDs

Publication Date



In this work, low-temperature photoconductivity measurements using excitation in the long-wavelength infrared were performed in conjunction with infrared-blocked band-gap excitation in the first studies of the energy transfer between carriers moving in lattice bands and those associated with an impurity band in a semiconductor. Extrinsic (impurity-band) excitations were produced in Si:As, Si:Bi, and Si:Al detectors by infrared photoexcitation at 29-33.5 μm wavelengths (37-43 meV); this could be augmented by simultaneous intrinsic (band-gap) photoexcitation using infrared-blocked white light to inject lattice-band carriers. Carrier transport was induced by applied electric fields of 35-175 V /cm. The experiments were performed at temperatures of 7-8 K, where thermal ionization of photoexcited impurity-band. carriers is unimportant, and also at 16 K, where thermal ionization is more significant. Although simplistic modeling indicates that impurity-band and lattice-band transport should be largely independent under the conditions of our experiments, we observed strong interactions in all cases studied. The presence of very shallow D-centers associated with the impurity band explains this result, which has important implications for certain proposed infrared detector designs. The effects of white light illumination on the temporal response of the detectors under pulsed infrared excitation were also investigated in this work. The results can be explained on the basis of a model in which lattice-band carriers interact with D- centers, in agreement with the conclusions of our spectral studies.

Document Type




Degree Name

Electrical Engineering

Level of Degree


Department Name

Electrical and Computer Engineering

First Committee Member (Chair)

John McIver

Second Committee Member

Kenneth Jungling

Third Committee Member

Donald Neaman

Third Advisor

Carroll Norris