Recombination lifetimes in gamma-irradiated silicon
Hewes, Ralph Allan
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https://hdl.handle.net/2142/25048
Description
Title
Recombination lifetimes in gamma-irradiated silicon
Author(s)
Hewes, Ralph Allan
Issue Date
1966
Doctoral Committee Chair(s)
Compton, W.D.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
recombination lifetimes
gamma-irradiated silicon
radiation induced lifetime changes
Language
en
Abstract
The small-signal recombination lifetimes of minority carriers were
measured as a function of temperature in silicon before and after irradiation
at room temperature by cobalt 60 gamma rays. The resistivity of
the boron doped samples ranged between 10 and 5000 ohm-cm, and the
resistivity of the phosphorus doped samples was between 20 and 220 ohm-cm.
Both crucible and floating zone grown materials were investigated.
The radiation induced lifetime changes were interpreted by the theory
of Hall, and Shockley and Read. The lifetime changes in n-type material
were interpreted to be due to two energy levels, one 0.17 ev from the
conduction band edge, which was assumed to be the substitutional oxygen
(A center) defect, and the other at 0.4 ev from the conduction band edge.
On the basis of annealing data, it appeared that the 0.4 ev level could be
due to several defects whose energy levels coincided, but that most of the
recombination in the float~zoned material occurred through the donor-vacancy
complex (E center). The introduction rates of the levels were not strongly
influenced by differences in resistivity, but the introduction rate of the
0.4 ev level was much less in material containing large oxygen concentrations.
Defects controlling the lifetime in irradiated p-type material were
placed at 0.18 ev above the valence band edge and at 0.3 ev below the
conduction band edge. The former level could possibly be located 0.18 ev
below the conduction band edge, but it is most unlikely that it is the A center
because of the ratio of the hole and electron Qapture cross-sections. The
0.18 ev level controlled the lifetime in the room temperature region in the
pulled material, and the 0.3 ev level controlled the lifetime at all measured
temperatures in float-zoned material whose resistivity was 70 ohm-em or
greater. The ratio of the hole to electron capture cross-section for the
0.3 ev level was about 20. No strong effect of resistivity was seen in
either of the p-type silicon, but the effect of the larger oxygen content
of the pulled material was to reduce the introduction rate of the 0.3 ev
level.
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