On the origin of 300 K near-band-edge luminescence in CdTe
A careful analysis of 300 K near-band-edge luminescence from bulk CdTe and cadmium telluride films is made. It is shown that: (i) the observed difference in 300 K peak positions of the near-band-edge luminescence hvm in CdTe crystals and films, and (ii) the hvm shift to lower energies as the excitat...
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| Опубліковано в: : | Semiconductor Physics Quantum Electronics & Optoelectronics |
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| Дата: | 2003 |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2003
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| Цитувати: | On the origin of 300 K near-band-edge luminescence in CdTe / K.D. Glinchuk, N.M. Litovchenko, O.N. Strilchuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2003. — Т. 6, № 4. — С. 441-443. — Бібліогр.: 14 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860036963063562240 |
|---|---|
| author | Glinchuk, K.D. Litovchenko, N.M. Strilchuk, O.N. |
| author_facet | Glinchuk, K.D. Litovchenko, N.M. Strilchuk, O.N. |
| citation_txt | On the origin of 300 K near-band-edge luminescence in CdTe / K.D. Glinchuk, N.M. Litovchenko, O.N. Strilchuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2003. — Т. 6, № 4. — С. 441-443. — Бібліогр.: 14 назв. — англ. |
| collection | DSpace DC |
| container_title | Semiconductor Physics Quantum Electronics & Optoelectronics |
| description | A careful analysis of 300 K near-band-edge luminescence from bulk CdTe and cadmium telluride films is made. It is shown that: (i) the observed difference in 300 K peak positions of the near-band-edge luminescence hvm in CdTe crystals and films, and (ii) the hvm shift to lower energies as the excitation intensity is increased, could not be satisfactory explained by an assumption that free excitons dominate in the formation of the above luminescence. So, the origin of 300 K near-band-edge luminescence in CdTe is not mainly the free exciton one as was proposed earlier, and needs further examination.
|
| first_indexed | 2025-12-07T16:54:37Z |
| format | Article |
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441© 2003, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
Semiconductor Physics, Quantum Electronics & Optoelectronics. 2003. V. 6, N 4. P. 441-443.
PACS: 78.55.-m ; 78.55. Et
On the origin of 300 K near-band-edge
luminescence in CdTe
K.D. Glinchuk, N.M. Litovchenko, O.N. Strilchuk
V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, 41, prospect Nauki, 03028 Kyiv, Ukraine
Phone : +380 (44) 2656373, fax: +380 (44) 2653337 (K.D. Glinchuk), E-mail: strilchuk@isp.kiev.ua
Abstract. A careful analysis of 300 K near-band-edge luminescence from bulk CdTe and
cadmium telluride films is made. It is shown that: (i) the observed difference in 300 K peak
positions of the near-band-edge luminescence hνm in CdTe crystals and films, and (ii) the hνm
shift to lower energies as the excitation intensity is increased, could not be satisfactory ex-
plained by an assumption that free excitons dominate in the formation of the above lumines-
cence. So, the origin of 300 K near-band-edge luminescence in CdTe is not mainly the free
exciton one as was proposed earlier, and needs further examination.
Keywords: 300 K near-band-edge luminescence, CdTe crystals and films, free excitons, emis-
sion intensities, exciton-phonon coupling.
Paper received 02.10.03; accepted for publication 11.12.03.
1. General remarks
The near-band-edge emission (its peak position hνm =
= 1.491�1.510 eV) is observed in 300 K luminescence
spectra of non-degenerated CdTe crystals and cadmium
telluride films (see, for example [1�4]). Some earlier [4],
an attempt was made to determine the origin of this emis-
sion. The authors of the cited paper [4] considered that
300 K near-band-edge emission from CdTe crystals and
films occurs mainly due to annihilation of free excitons
in the n = 1 ground state (further X1 excitons) and the
n = 2 excited state (further X2 excitons) with only limited
contribution (up to 30%) of band-to-band transitions, as
the luminescence peak energy is less that 300 K CdTe
bandgap Eg = 1.513 eV. Then, to explain the observed
emission regularities (see Figs 1 and 2): (i) the difference
in hνm values for CdTe films and crystals, and (ii) the
shift of hνm values to lower energies with the growing
excitation intensity L (power density P), they assumed
the following. (a) A strong free exciton-phonon coupling
exists in CdTe crystals, but not in CdTe films (this obvi-
ously shifts the discussed spectrum to lower energies),
and (b) the excitation-induced change in the contribu-
tion (i.e. in a relative strength) of free excitons in n = 1
and n =2 states to the formation of the near-band-edge
emission. But practically no careful analysis confirming
the adopted suppositions was made. In this paper, a de-
tailed analysis of assumptions made in [4] will be given.
On its basis, we will show that the dominant free exciton
contribution in the formation of the 300 K near-band-
edge CdTe emission cannot explain the regularities ob-
served when the cadmium telluride type (crystal or film)
and the excitation intensity are varied. So, the nature of
recombination transitions leading to a formation of 300 K
cadmium telluride near-band-edge emission needs
reexamination.
2. On the free exciton-phonon coupling in CdTe
The free exciton-phonon coupling (phonon-assisted
radiative transitions, i.e. phonon replicas of emission
lines) could really be observed in 4.2 K luminescence
spectra of both CdTe films and crystals (see, for exam-
ple, [5�9]). Obviously, it is difficult to observe directly
the exciton-phonon coupling at the room temperature due
to a considerable thermal broadening of the free exciton
induced emission lines. But there is no obvious reason to
suppose that the free exciton-phonon coupling could dif-
fer in bulk CdTe and cadmium telluride films (in any
case, this conclusion should be made from the direct ob-
servation of 4.2 K free exciton-induced luminescence
spectra of CdTe films and crystals; but unfortunately, no
free exciton recombination lines were resolved in 4.2 K
luminescence spectra of CdTe films and crystals investi-
442
SQO, 6(4), 2003
K.D. Glinchuk et al.: On the origin of 300 K near-band-edge luminescence in CdTe
gated in the discussed paper [4]). Moreover, nearly the
same free exciton-phonon coupling is observed in experi-
ment in 4.2 K luminescence spectra of cadmium telluride
films [7] and crystals [5,6,8,9]. So, it seems to us that the
proposed in [4] explanation of different peak positions in
300 K near-band-edge emission for bulk CdTe and cad-
mium telluride films as arising due to a different free
exciton-phonon coupling in them could not be taken as a
correct one, i.e. as well grounded.
3. Intensities of free exciton-induced emission
bands in the near-band-edge luminescence
spectra of non-degenerate semiconductors
Let us consider non-degenerate semiconductors (where
concentrations of equilibrium free electrons and holes are
n0 and p0 and of non-equilibrium δn and δp). Let the
excitonic luminescence spectrum be formed by annihila-
tion of thermalized free excitons (their distribution is given
by the Maxwell-Boltzmann function) in the ground state
n = 1 (their excess concentration nX1, binding energy εX1,
a probability of radiative annihilation aX1), and the ex-
cited state n = 2 [their excess concentration nX2, binding
energy εX2, a probability of radiative annihilation αX2
[naturally, αX2 < αX1 (αXn ~ 1/n3 for allowed direct
transitions as follows from the well-known correlation
between the free exciton absorption coefficient and the
luminescence intensity [10])]. Obviously, for the discussed
case, emission intensities induced by annihilation of free
excitons in the ground (IX1) and excited (IX2) states are:
IX1 = αX1nX1 , (1)
IX2 = αX2nX2 . (2)
To find the IX1 and IX2 dependence on L, one should
obtain nX1 and nX2 values (obviously, they are determined
by the rates of free exciton generation, their radiative
annihilation and thermal dissociation). They could be
found from the following kinetic equations (see also [11-
13] ):
1
1 0 0 1 1 1( ) ( )X
X X X X
dn
b n p p n p n q n
dt
δ δ δ δ α= + + − + = 0,
(3)
2
2 0 0 2 2 2( ) ( )X
X X X X
dn
b n p p n p n q n
dt
δ δ δ δ α= + + − + = 0,
(4)
where bX1 and bX2 are the probabilities of binding of free
electrons and holes into free excitons in the ground and
excited states (obviously, bX1 > bX2) , qX1 and qX2 are the
probabilities of thermal dissociation of X1 an X2 excitons
on free electrons and holes (obviously, qX1 < qX2) {a defi-
nite correlation between qX1 and bX1 [qX1= *
1 1X Xn b , where
* *
1 1exp( / )X X Xn N kTε= − ], qX2 and bX2 [qX2= *
2 2X Xn b ,
where * *
2 2exp( / )X X Xn N kTε= − ] ( *
XN = 2 3/2( / 2 )rm kT πh =
=2.4⋅1015 (mr /m0)3/2T 3/2 cm�3 , where mr = memh/(me +
+ mh) is the reduced exciton mass) exists [11�13]}. When
writing Eqs (3) and (4), we assumed that direct annihila-
1.45 1.50 1.55 1.60
b
1.492
hn , eV
I
,
a
r
b
.u
n
it
s
1.506
a
Fig. 1. Representative 300K photoluminescence from CdTe film
(a) and bulk CdTe (b) in a region of hνm independent on the
=excitation intensity [4].
1
2
0
1.485
1.490
1.495
1.500
1.505
1.510
20 40 60 80
2
Fig.2. Excitation power dependence of 300 K emission peak
energy for CdTe film (1) and bulk CdTe (2) [4].
K.D. Glinchuk et al.: On the origin of 300 K near-band-edge luminescence in CdTe
443SQO, 6(4), 2003
tion of free excitons proceeds mainly with the photon
emission and took into account that quasi-equilibrium
exists between thermalized free excitons in n =1 and n =
2 states.
Solving Eqs (3) and (4) one finds the nX1 and nX2
values. They are:
1
1 0 0
1 1
( )X
X
X X
b
n n p p n p n
q
δ δ δ δ
α
= + +
+
=
1
0 0*
1 1 1
( )X
X X X
b
n p p n p n
n b
δ δ δ δ
α
= + +
+
, (5)
2
2 0 0
2 2
( )X
X
X X
b
n n p p n p n
q
δ δ δ δ
α
= + +
+
=
2
0 0*
2 2 2
( )X
X X X
b
n p p n p n
n b
δ δ δ δ
α
= + +
+
, (6)
So, as one can see from Eqs (1), (2), (5) and (6), a
relation between intensities IX1 and IX2 does not depend
on the excitation intensity L, i.e.
IX1 : IX2 = αX1
1
1 1
X
X X
b
qα +
: αX2
2
2 2
X
X X
b
qα +
=
1 2
1 2* *
1 1 1 2 2 2
:X X
X X
X X X X X X
b b
n b n b
α α
α α
=
+ +
≠ ϕ(L)
(7)
{the validity of the obtained correlation IX1 : IX2 ≠ ϕ(L)
follows also from the direct calculation of IX1 and IX2
values from the well-known relation between the absorp-
tion coefficient and the recombination rate using detailed
balance arguments [10,12,14]}.
Therefore, the free exciton-induced luminescence spec-
trum in semiconductors, in particular, in CdTe, does not
change its shape with excitation, i.e. the relative weight
of recombination flows via n = 1 (IX1) and n = 2 (IX2)
excitonic states {obviously, IX1 > IX2 at any L [see Eq.
(7)] contrary to the accepted in [4]}, is not influenced by
the excitation intensity. So, the proposed in [4] explana-
tion of 300 K hνm shift with L in CdTe as connected with
the excitation-induced redistribution of recombination
flows via n = 1 and n = 2 free exciton states, is not well
founded. So, free excitons could bring a definite, but not
the dominating contribution into the formation of 300 K
near-band-edge luminescence of cadmium telluride.
4. Conclusion
300 K near-band-gap luminescence in cadmium telluride
crystals and films does not originate as a result of domi-
nating free exciton transitions (they bring some but not
the dominating contribution). Further investigations are
needed to arrive at the exact origin of 300 K near-band-
edge luminescence from cadmium telluride. One of them
concerns the detailed measurement of temperature-in-
duced (in the range of 4.2 to 300 K) variations in the
intensity and the line shape of the free exciton (as well as
bound exciton) emissions and band-to-band transitions
from cadmium telluride crystals and films. It will permit
to find the exact contribution to 300 K near-band-edge
luminescence from CdTe of free and bound excitons, band-
to-band and band-to-band tail states.
References
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| id | nasplib_isofts_kiev_ua-123456789-118083 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1560-8034 |
| language | English |
| last_indexed | 2025-12-07T16:54:37Z |
| publishDate | 2003 |
| publisher | Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| record_format | dspace |
| spelling | Glinchuk, K.D. Litovchenko, N.M. Strilchuk, O.N. 2017-05-28T16:41:27Z 2017-05-28T16:41:27Z 2003 On the origin of 300 K near-band-edge luminescence in CdTe / K.D. Glinchuk, N.M. Litovchenko, O.N. Strilchuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2003. — Т. 6, № 4. — С. 441-443. — Бібліогр.: 14 назв. — англ. 1560-8034 PACS: 78.55.-m ; 78.55. Et https://nasplib.isofts.kiev.ua/handle/123456789/118083 A careful analysis of 300 K near-band-edge luminescence from bulk CdTe and cadmium telluride films is made. It is shown that: (i) the observed difference in 300 K peak positions of the near-band-edge luminescence hvm in CdTe crystals and films, and (ii) the hvm shift to lower energies as the excitation intensity is increased, could not be satisfactory explained by an assumption that free excitons dominate in the formation of the above luminescence. So, the origin of 300 K near-band-edge luminescence in CdTe is not mainly the free exciton one as was proposed earlier, and needs further examination. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics On the origin of 300 K near-band-edge luminescence in CdTe Article published earlier |
| spellingShingle | On the origin of 300 K near-band-edge luminescence in CdTe Glinchuk, K.D. Litovchenko, N.M. Strilchuk, O.N. |
| title | On the origin of 300 K near-band-edge luminescence in CdTe |
| title_full | On the origin of 300 K near-band-edge luminescence in CdTe |
| title_fullStr | On the origin of 300 K near-band-edge luminescence in CdTe |
| title_full_unstemmed | On the origin of 300 K near-band-edge luminescence in CdTe |
| title_short | On the origin of 300 K near-band-edge luminescence in CdTe |
| title_sort | on the origin of 300 k near-band-edge luminescence in cdte |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/118083 |
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