Transient photoconductivity in silver chloride at low temperatures
Van Heyningen, Roger Steven
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https://hdl.handle.net/2142/16608
Description
Title
Transient photoconductivity in silver chloride at low temperatures
Author(s)
Van Heyningen, Roger Steven
Issue Date
1958
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
silver chloride
Transient photoconductivity
Language
en
Abstract
Primary photoconductivity in single crystals of pure AgCl has been investigated in the temperature range 6.5°K to 80°K by using low intensity monochromatic light pulses and a. sensitive electrometer. In the region of fundamental optical absorption, the photoresponse as a function of wavelength and applied electric field has been found to be strongly dependent on the condition of the illuminated surface. This behavior may be explained by a theory in which it is assumed that a thin layer near the surface has a different density of traps than the volume of the crystal. The range of electrons was found to be long in an air grown crystal, ~10^-3 cm2/volt, and relatively short in a vacuum grown crystal, ~10^-6 cm2/volt, at 80°K. In both air and vacuum grown crystals the range of holes was not measurable. At 80°K an upper limit for hole range of ~10^-8 cm2/volt was established. The yield of free electrons per absorbed photon (quantum efficiency) as a function of wavelength and temperature has 'been determined from the experiment. In all crystals the measured quantum efficiency showed structure and was high, decreasing from ~0.7 at the optical absorption edge through the first absorption peak to ~ 0.1 at 220mµ. The quantum efficiency was the same at 35°K as at 80°K and was comparable at 6. 5°K. . There was no evidence that the quantum efficiency decreased in the absorption peak with decreasing temperature. Trapping greatly reduced the electron range at low temperatures (~10^-3 cm2/volt at 80°K; ~10^-9 cm2/volt at 6.5°K). Characteristics of the most important traps can be deduced from prominent electrical glow peaks at 15°K, 36°K, and 180°K, as well as from current decay measurements and trap filling experiments at fixed temperatures. The deep, 0.55 ev, traps are present in concentrations of ~10^10 cm^-3 (air grown crystals) to ~10^13 cm^-3 (vacuum grown crystals) and have a large cross section, ~10^-12 cm2. The shallow traps are in much higher concentration.
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