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PHOTOCONDUCTIVITY AND NOISE IN TELLURIUM,
MICHIGAN UNIV ANN ARBOR INST OF SCIENCE AND TECHNOLOGY
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Certain electrical properties of single-crystal tellurium in the extrinsic temperature range have been measured and interpretated theoretically. The chief object of study was the effect of ther mal and optical excitation upon electrical con ductivity in its steady-state, transient, and randomly fluctuating aspects. The steady-state photoconductivity response is proportional to the first power of the intensity of the light for low excitation, becoming proportional to the square root of the intensity for conductance changes greater than 2. The small-signal re ponsive time constant is about 350 micro sec for T less than 80 K in the dark, decreasing rapidly with either thermal or steady optical excita tion. A model composed of 5 million millionths traps cc of energy level 0.072 ev above the valence band and an unspecified recombination mechanism account quantitatively for the observed steady-state and transient behavior. The elec trical noise power due to conductivity fluctua tions is measured in the dark as a function of temperature and at 79 K as a function of steady optical excitation. The dark noise is interpre ted quantitatively in terms of electron transit ions between the valence band and traps of ener gy level about 0.045 ev above it. The additional noise dut to steady optical excitation at 79 K is attributed to transverse carrier-density gradi ents resulting from nonuniform excitation. Author
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