SEMICONDUCTORS. DIELECTRICS
Dislocation spectroscopy of crystals
S. Z. Shmurak
Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow District,
Russia
͑Submitted March 5, 1999; resubmitted April 21, 1999͒
Fiz. Tverd. Tela ͑St. Petersburg͒ 41, 2139–2146 ͑December 1999͒
A new method of studying the energy characteristics of dislocations is proposed, which is based
on the investigation of the interaction of moving dislocations with purposefully introduced
electronic and hole centers. A study has been made of KCl, NaCl, KBr, LiF, and KI alkali halide
crystals containing electronic F and hole V
K
and Me
ϩϩ
(Cu
ϩϩ
,Ag
ϩϩ
,Tl
ϩϩ
,In
ϩϩ
) centers.
Investigation of the temperature dependence of the dislocation interaction with the F centers
permitted determination of the position of the dislocation-induced electronic band ͑DEB͒ in
the band diagram of the crystal. In KCl, the DEB is separated by Ϸ2.2eV from the conduction-
band minimum. It is shown that dislocations transport holes from the centers lying below
the dislocation-induced hole band ͑DHB͒ (X
ϩ
,In
ϩϩ
,Tl
ϩϩ
, V
K
) to those above the DHB ͑the Cu
ϩ
and Ag
ϩ
centers͒. Such a process is temperature independent. The DHB position in the
crystal band diagram has been determined; in KCl it is separated by Ϸ1.6eV from the valence-
band top. The effective radii of the dislocation interaction with the electronic F and hole
X
ϩ
, V
K
, and Tl
ϩϩ
centers have been found. © 1999 American Institute of Physics.
͓S1063-7834͑99͒00812-6͔
Dislocations are known to affect considerably the elec-
tronic spectrum of a crystal, thus inducing a change of many
physical properties ͑electrical, optical, and magnetic͒ of the
latter.
A number of processes are stimulated by moving dislo-
cations. When dislocations move in colored alkali halide
͑AH͒ crystals, one observes emission of photons and elec-
trons accompanied by annihilation of some centers, e.g. of F
and V
K
, and creation of others (Cu
ϩϩ
,Ag
ϩϩ
).
1–4
In ZnS
crystals, moving dislocations give rise to the onset of tran-
sient and steady-state dislocation-induced luminescence,
electron emission, electroplastic effect odd in the field, and
structural rearrangements in the crystal.
5–7
In order to identify the mechanisms responsible for the
effect of dislocations on the physical properties of crystals,
one has first of all to understand the way in which the dislo-
cations change the energy spectrum of a crystal. Unfortu-
nately, despite a wealth of publications dealing with the in-
fluence of dislocations on the physical properties of crystals,
the information on the energy characteristics of dislocations
is extremely scant.
The present work proposes a new method for determin-
ing the energy characteristics of dislocations, which is based
on studying dislocation interaction with centers introduced
purposefully into AH crystals. In this way electronic and
hole centers with known energy characteristics are created in
a crystal. Next one investigates the variation with tempera-
ture of the concentration of these centers after the moving
dislocations have interacted with them. The electronic and
hole centers act in this process as energy ‘‘tags.’’ This tech-
nique permits one to obtain information on the energy pa-
rameters of the electronic and dislocation-induced hole bands
in the band diagram of the crystal. Another merit of this
method is that in this way one can determine the energy
characteristics of moving dislocations, which are free of the
impurities decorating them when they are immobile.
1. DISLOCATION INTERACTION WITH THE ELECTRONIC
AND HOLE CENTERS IN IONIC CRYSTALS
Theoretical treatment of the effect of such a complex
system as the dislocation on the spectrum of electronic states
is a very serious problem even in the case of alkali halide
crystals, whose band diagram is studied in considerable de-
tail and the dislocation structures are known.
Quantum mechanical calculations show the existence on
dislocations of bound states of both electrons and holes.
8,9
However the binding energies determined in these studies
should be considered only as order-of-magnitude estimates,
because they make use of the short-range ͑deformation͒ po-
tential approximation. At the same time an analysis shows
the radius of the carrier bound state to be of the order of the
lattice constant, which renders the starting approximation in-
valid. Therefore experimental investigation of the dislocation
energy characteristics obtained by studying the interaction of
moving dislocations with the electronic and hole centers is of
considerable interest for physics of the solid state.
A moving dislocation always interacts with electronic
and hole centers. Obviously enough, if the energy level of an
electronic center ͑EC͒ lies above the dislocation-induced
electronic band (D
e
), the dislocation will capture an electron
PHYSICS OF THE SOLID STATE VOLUME 41, NUMBER 12 DECEMBER 1999
19631063-7834/99/41(12)/7/$15.00 © 1999 American Institute of Physics