The relaxation of photodarkening (PD) brought about by above-bandgap and sub-bandgap excitations is studied in a wide temperature range in amorphous selenium (a-Se) films designed for avalanche photodetectors. The experimental results suggest that in contrast to sub-bandgap excitation, above-bandgap excitation does not cause the formation of self-trapped excitons, viz., photoinduced transformation of the a-Se ground state configuration into a metastable higher-energy configuration. For above-bandgap excitation only transient PD is observed, and its subsequent relaxation can be explained by thermalization and energy relaxation of uncorrelated carriers through the band-tails in order to restore the ground state configuration. In contrast, sub-bandgap excitation causes both transient and reversible PD, with the latter controlled by the formation of self-trapped excitons, whose relaxation requires overcoming an energy barrier of 0.78 ± 0.02 eV either by thermal activation (at elevated temperatures) or by configurational tunneling (for temperatures below room temperature).

1.
S.
Kasap
,
J. B.
Frey
,
G.
Belev
,
O.
Tousignant
,
H.
Mani
,
J.
Greenspan
,
L.
Laperriere
,
O.
Bubon
,
A.
Reznik
,
G.
DeCrescenzo
 et al., “
Amorphous selenium and its alloys from early xeroradiography to high resolution X-ray image detectors and ultrasensitive imaging tubes
,”
Phys. Status Solidi B
246
(
8
),
1794
1805
(
2009
).
2.
K.
Tanioka
,
J.
Yamazaki
,
K.
Shidara
,
K.
Taketoshi
,
T.
Kawamura
,
S.
Ishioka
, and
Y.
Takasaki
,
IEEE Electron Device Lett.
8
,
392
(
1987
).
3.
N. F.
Motta
,
E. A.
Davisa
, and
R. A.
Street
, “
States in the gap and recombination in amorphous semiconductors”
,
Philos. Mag.
32
,
961
996
(
1975
).
4.
A.
Kolobov
, “
Chalcogenides Metastability and Phase Change Phenomena
”, Material Science Vol.
164
(
Springer
,
2012
), Chap. 4.
5.
K.
Tanaka
, “
Mechanisms of photodarkening in amorphous chalcogenides
”,
J. Non-Cryst. Solids
59&60
,
925
928
(
1983
).
6.
K.
Tanaka
,
J. Appl. Phys.
65
,
2042
(
1989
).
7.
V. K.
Tikhomirov
,
G. J.
Adriaenssens
, and
S. R.
Elliott
, “
Temperature dependence of the photoinduced anisotropy in chalcogenide glasses: Activation energies and their interpretation
,”
Phys. Rev. B
55
,
R660
R663
(
1997
).
8.
D. K.
Biegelsen
and
R. A.
Street
, “
Photoinduced defects in chalcogenide glasses
,”
Phys. Rev. Lett.
44
(
12
),
803
806
(
1980
).
9.
R. A.
Street
, “
Non-radiative recombination in chalcogenide glasses
,”
Solid State Commun.
24
,
363
365
(
1977
).
10.
V. L.
Averianov
,
A. V.
Kolobov
,
B. T.
Kolomiets
, and
V. M.
Lyubin
,
Phys. Status Solidi A
57
,
81
(
1980
).
11.
K.
Tanaka
and
A.
Odajima
,
Solid State Commun.
43
,
961
(
1982
).
12.
K.
Shimakawa
,
S.
Inami
, and
S. R.
Elliott
,
Phys. Rev. B
42
,
11857
(
1990
).
13.
A.
Reznik
,
B. J. M.
Lui
,
J. A.
Rowlandsal
,
S. D.
Baranovskii
,
O.
Rubel
,
V.
Lyubin
,
M.
Klebanov
,
S. O.
Kasap
,
Y.
Ohkawa
,
T.
Matsubara
 et al.,
J. Appl. Phys.
100
,
113506
(
2006
).
14.
H.
Fritzsche
, “
The origin of reversible and irreversible photostructural changes in chalcogenide glasses
,”
Philos. Mag. B
68
(
4
),
561
572
(
1993
).
15.
K.
Tanaka
,
Jpn. J Appl. Phys., Part 1
25
,
779
(
1986
).
16.
Z. U.
Borisova
,
Glassy Semiconductors
(
Plenum
,
New York
,
1981
).
17.
A.
Reznik
,
S. D.
Baranovskii
,
M.
Klebanov
,
V.
Lyubin
,
O.
Rubel
, and
J. A.
Rowlands
, “
Reversible vs irreversible photodarkening in a-Se: the kinetics study
,”
J. Mater. Sci.: Mater. Electron
20
,
S111
S115
(
2009
).
18.
V. K.
Tikhomirov
and
S. R.
Elliot
, “
Model for photoinduced anisotropy and its dark relaxation in chalcogenide glasses
,”
Phys. Rev. B
51
(
8
),
5538(R)
(
1995
).
19.
D. E.
Ackley
,
J.
Tauc
, and
W.
Paul
, “
Picosecond relaxation of optically induced absorption in amorphous semiconductors
,”
Phys. Rev. Lett.
43
,
715
718
(
1979
).
20.
C.
Tsang
and
R. A.
Street
, “
Recombination in plasma-deposited amorphous Si:H. Luminescence decay
,”
Phys. Rev. B
19
,
3027
3040
(
1979
).
21.
J.
Berashevich
,
A.
Mishchenko
, and
A.
Reznik
, “
Two-Step Photoexcitation Mechanism in Amorphous Se
”,
Phys. Rev. Appl.
1
,
034008
(
2014
).
You do not currently have access to this content.