Influence of complex defects on electrophysical properties of GaP light emitting diodes
In order to estimate the role of complex defects on GaP light emitting diodes (LED) operation, luminescent and electrical characteristics of GaP LEDs irradiated with reactor neutrons have been studied. It has been stated that nonradiative levels of radiation defects affect electroluminescence que...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2014
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| Cite this: | Influence of complex defects on electrophysical properties of GaP light emitting diodes / O. Konoreva, E. Malyj, S. Mamykin, I. Petrenko, M. Pinkovska, V. Tartachnyk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2014. — Т. 17, № 2. — С. 184-187. — Бібліогр.: 9 назв. — англ. |
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Konoreva, O. Malyj, E. Mamykin, S. Petrenko, I. Pinkovska, M. Tartachnyk, V. 2017-05-30T06:02:12Z 2017-05-30T06:02:12Z 2014 Influence of complex defects on electrophysical properties of GaP light emitting diodes / O. Konoreva, E. Malyj, S. Mamykin, I. Petrenko, M. Pinkovska, V. Tartachnyk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2014. — Т. 17, № 2. — С. 184-187. — Бібліогр.: 9 назв. — англ. 1560-8034 PACS 29.40.-n, 85.30.-z, 85.60.Dw https://nasplib.isofts.kiev.ua/handle/123456789/118369 In order to estimate the role of complex defects on GaP light emitting diodes (LED) operation, luminescent and electrical characteristics of GaP LEDs irradiated with reactor neutrons have been studied. It has been stated that nonradiative levels of radiation defects affect electroluminescence quenching. From the analysis of the tunnel current, the density of dislocations in the depleted part of the p–n junction was obtained. Neutron induced disorder regions do not change the tunnel component of the direct current of red diodes, increasing the dislocation density, because the carrier flow along the “tunnel shunts” is blocked. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics Influence of complex defects on electrophysical properties of GaP light emitting diodes Article published earlier |
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Influence of complex defects on electrophysical properties of GaP light emitting diodes |
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Influence of complex defects on electrophysical properties of GaP light emitting diodes Konoreva, O. Malyj, E. Mamykin, S. Petrenko, I. Pinkovska, M. Tartachnyk, V. |
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Influence of complex defects on electrophysical properties of GaP light emitting diodes |
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Influence of complex defects on electrophysical properties of GaP light emitting diodes |
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Influence of complex defects on electrophysical properties of GaP light emitting diodes |
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Influence of complex defects on electrophysical properties of GaP light emitting diodes |
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influence of complex defects on electrophysical properties of gap light emitting diodes |
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Konoreva, O. Malyj, E. Mamykin, S. Petrenko, I. Pinkovska, M. Tartachnyk, V. |
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Konoreva, O. Malyj, E. Mamykin, S. Petrenko, I. Pinkovska, M. Tartachnyk, V. |
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2014 |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Article |
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In order to estimate the role of complex defects on GaP light emitting diodes
(LED) operation, luminescent and electrical characteristics of GaP LEDs irradiated with
reactor neutrons have been studied. It has been stated that nonradiative levels of radiation
defects affect electroluminescence quenching. From the analysis of the tunnel current,
the density of dislocations in the depleted part of the p–n junction was obtained. Neutron
induced disorder regions do not change the tunnel component of the direct current of red
diodes, increasing the dislocation density, because the carrier flow along the “tunnel
shunts” is blocked.
|
| issn |
1560-8034 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/118369 |
| citation_txt |
Influence of complex defects on electrophysical properties of GaP light emitting diodes / O. Konoreva, E. Malyj, S. Mamykin, I. Petrenko, M. Pinkovska, V. Tartachnyk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2014. — Т. 17, № 2. — С. 184-187. — Бібліогр.: 9 назв. — англ. |
| work_keys_str_mv |
AT konorevao influenceofcomplexdefectsonelectrophysicalpropertiesofgaplightemittingdiodes AT malyje influenceofcomplexdefectsonelectrophysicalpropertiesofgaplightemittingdiodes AT mamykins influenceofcomplexdefectsonelectrophysicalpropertiesofgaplightemittingdiodes AT petrenkoi influenceofcomplexdefectsonelectrophysicalpropertiesofgaplightemittingdiodes AT pinkovskam influenceofcomplexdefectsonelectrophysicalpropertiesofgaplightemittingdiodes AT tartachnykv influenceofcomplexdefectsonelectrophysicalpropertiesofgaplightemittingdiodes |
| first_indexed |
2025-11-26T00:08:25Z |
| last_indexed |
2025-11-26T00:08:25Z |
| _version_ |
1850592170698866688 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 2. P. 184-187.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
184
PACS 29.40.-n, 85.30.-z, 85.60.Dw
Influence of complex defects on electrophysical properties
of GaP light emitting diodes
O. Konoreva1, E. Malyj1, S. Mamykin2,*, I. Petrenko1, M. Pinkovska1, V. Tartachnyk1
1Institute for Nuclear Researches, NAS of Ukraine,
47, prospect Nauky, 03028 Kyiv, Ukraine
2V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine,
41, prospect Nauky, 03028 Kyiv, Ukraine
*Corresponding author phone: +38(044)-525-37-49; e-mail: myrglory@yahoo.com
Abstract. In order to estimate the role of complex defects on GaP light emitting diodes
(LED) operation, luminescent and electrical characteristics of GaP LEDs irradiated with
reactor neutrons have been studied. It has been stated that nonradiative levels of radiation
defects affect electroluminescence quenching. From the analysis of the tunnel current,
the density of dislocations in the depleted part of the p–n junction was obtained. Neutron
induced disorder regions do not change the tunnel component of the direct current of red
diodes, increasing the dislocation density, because the carrier flow along the “tunnel
shunts” is blocked.
Keywords: gallium phosphide, light emitting diode, defect, luminescence and quantum
yield.
Manuscript received 21.01.14; revised version received 12.05.14; accepted for
publication 12.06.14; published online 30.06.14.
1. Introduction
The external quantum yield of light emitting diode
(LED), which determines its effectiveness, depends on
three factors: Е = іlo, where і is the coefficient of
minority carrier injection, l – effectiveness of light
generation and о – coefficient of light output. The first
and second multipliers characterize the quality of the
crystal and p–n junction and are usually combined as the
internal quantum yield I = іl [1].
It is more difficult to control a commercial device
than a separate crystal, especially if complex defects
such as dislocations, radiation induced defects and other
ones are available and dominate in device properties.
One should know that defects of “dark line” and “dark
spot” types, responsible for degradation processes in
GaP LEDs, are caused by the accumulation of
dislocation networks [2].
While creating the p–n junction in LEDs, layers of
different conductivity are deposited epitaxially on
substrate. Due to the interface between these two films,
defects are accumulated within the depleted region of
transition at a distance of 2-3 diffusion lengths from this
interface. It negatively affects the value of the internal
quantum yield.
The situation is still worsening due to the growth of
dislocations out of the substrate surface, which is
previously polished and possesses a great amount of
line-type defects ( > 106 cm–2). In order to eliminate the
influence of the substrate surface, it is unreasonable to
increase the n-film thickness, because self-absorption of
photons will increase.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 2. P. 184-187.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
185
Therefore, we hope that the study of behavior of
dislocations in the transition region will help to predict
the LED performance.
The authors of the papers [3, 4] showed the
possibility of appearance of the excess direct tunnel
current not only in degenerate p–n–n junctions and
heterostructures. It turns out that the model of
“dislocation shunt”, which describes interdefect
tunneling of carriers in the space charge region, can be
applied to the homojunction where the tunneling process
occurs along the dislocation line.
Based on the conclusions obtained in [3, 4], one
can appreciate the density of dislocations in the p–n
junction and identify the impact of extreme external
factors (including also fast particle irradiation – in this
case) on interdislocation tunneling of carriers.
We have presented the results of the study of
electroluminescence spectra and electrophysical
characteristics of GaP LEDs irradiated with fast reactor
neutrons. Current-voltage characteristics of initial diodes
and those with radiation defects have been analyzed
using the method proposed in the paper [4], and the
dislocation influence has been estimated as well.
2. Experimental
We studied green and red industrial LEDs made using
double solid epitaxial methods. Green LEDs were doped
with nitrogen atoms, red – with zinc and oxygen,
simultaneously. The electron concentration was equal to
317 cm102 , and that of holes – 316cm1054 . The
n-GaP substrate was made using the Czochralsky
method with the carrier concentration 317 cm1075 .
The sample dimensions were 1×1 mm. The diodes were
irradiated with fast neutrons in reactor at room
temperature. Current-voltage characteristics were
measured manually and by the automatic system within
the range A10...1 9 for current and 1 to 30 V – for
voltage at temperatures ranging from 77 up to 300 K.
Electroluminescence spectra were measured by a
spectrometer BLK-C F1000-VIS NIR-1 (StellarNet Inc)
for 190…850 nm intervals within the same temperature
range 77 to 300 K.
3. Result and discussion
The electroluminescence spectra of green GaP LEDs
measured at room and nitrogen temperatures are given in
Fig. 1. As one can see, the low temperature spectrum
possesses a fine structure due to izoelectron nitrogen
impurity. In the near-edge part of the spectrum, there is a
line associated with exciton bound to nitrogen atom. Its
intensity is significantly weaker than luminosity of
exciton bound to the pair of NNi centers due to the lower
binding energy and effect of self-absorption. When the
sample temperature increases up to 300 K, the fine
structure of the spectrum disappears.
Fig. 1. Electroluminescence spectrum of GaP LED at 300 and
77 K.
The main emission band is related with the pair
NN1. It has E = 2.22 eV and LA line as phonon
duplication.
Irradiation of GaP LED with fast reactor neutrons
causes a monotonic intensity drop of all the lines, and
the luminosity of exciton bound to the isolated nitrogen
atom is the most sensitive region of the spectrum to
introduction of radiation defects.
It was stated in [5] and confirmed later by us and
other authors [6-9] that the radiationless level of
radiation defects is a reason for electroluminescence
quenching.
It should be said that impurity levels existing in the
forbidden band of non-irradiated diode can also be the
centers of nonradiative recombination and reduce the
internal quantum yield.
It was found [2] that the low value of the internal
quantum yield of irradiated GaP LEDs was due to deep
levels caused mainly by dislocations in the np
junction, the thickness of which was of the order of the
diffusion length inherent to minority carriers.
Excess tunneling through the depleted region of the
diode is a component of the injection current and can
exist not only in the degenerate structures. Even at base
moderate doping of the p–n junction (order 317 cm10 ),
this opportunity may be provided by hopping-like
tunneling through the space charge region [3, 4].
In the dislocation shunt model, the exponential part
of the current-voltage characteristics is described as
follows:
1exp0
eV
II .
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 2. P. 184-187.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
186
Here, unlike the Shockley formula, І0 is the
function not only of diffusion and electric constants of
the base:
ceV
eI expD0 ,
where is the dislocation density, – characteristic
energy, D – Debye frequency, and е – electron charge.
The contact potential difference Vc (like to the
classical model) may be given in the form of
,lnlnln
lnlnln
2
p
V
n
Cg
g
VC
np
i
np
i
n
i
p
c
p
N
n
N
e
kT
e
E
kT
E
eNN
np
e
kT
n
np
e
kT
n
n
n
p
e
kT
V
where Еg is the band gap; NC, NV are densities of states in
the appropriated conduction and valence bands; nn, pp
are concentrations of electrons and holes, respectively.
Considering the GaP temperature dependence of
the band gap Eg = Eg(0) – T, where is a constant, one
can define the parameter and dislocation density:
gg
kT
VC
pn E
NN
pn
e
I
exp
D
0 .
GaP current-voltage characteristics of green (active
region is doped with nitrogen), red (doped with both zinc
and oxygen) and the same diode irradiated with fast
reactor neutrons (E = 1 MeV, F = 216cm10 ) are given
in Fig. 2.
Fig. 2. Current-voltage characteristics of GaP LED diode:
irradiated with fast reactor neutrons (1); initial red (2) and
green (3) diodes.
In the latter case, the neutron dose was so high that
the diode stopped emitting even at significant levels of
injection (I = 50…60 mA). By extrapolating the
exponential plot of the current-voltage dependence on
the zero displacement, it is possible to obtain І0, where
is the curve slope. Measurements carried out within the
range 77…300 K showed that both the parameters did
not practically depend on temperature. Considering that
NV = NC = 318cm108 and n p 317 cm10 ,
corresponding to the mean value of the carrier
concentration in the base of the diodes of AL-102 BM
series, the average dislocation density in green GaP(N)
is equal to D = 210 cm105.7 , in red GaP (Zn-O) D =
28cm104 .
After neutron irradiation of red diodes, D is equal
to 28cm104.4 .
So, it is obvious that in red diodes neutrons do not
appreciably affect the density of linear defects –
dislocations, despite the fact that thermal wedges and
associated deformation fields or Brinkman peaks of
displacements appear in irradiated objects.
It is also obvious that under neutron irradiation the
crystal structure becomes so disordered that tunnel
jumps, occuring in non-irradiated crystal along the
dislocation tubes, become impossible due to fractures of
dislocation lines. An additional increase of dislocation
densities in the periphery areas of disordered regions
does not affect the value of the tunnel component of the
direct current. “Dislocation shunt” does not work within
the space charge region.
4. Conclusions
Main lines of electroluminescence spectra of green
GaP(N) LEDs have been identified at different
temperatures. At 77 K, the thin structure was discovered
with the peak associated with exciton bound to separate
nitrogen atom. Its intensity is significantly weaker than
that of exciton bound to the pair of NN centers due to the
lower binding energy and effect of self-luminosity. The
structure vanishes when temperature increases up to
300 K. Neutron irradiation causes monotonic quenching
of all the components in the electroluminescence
spectrum.
The model of dislocation tunneling makes it
possible to assess the density of dislocations in the
depleted part of the np junction. This value D is
close to 210 cm105.7 in green GaP(N) and in red GaP
(Zn-O) – 28cm104 . Neutron irradiation does not
significantly affect D of red diodes.
It has been suggested that the disorder regions
induced with neutrons are able to block the current flow
along the “tunnel shunts”.
The authors thank to M. Lytovchenko for his help
in carrying out the experiment.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 2. P. 184-187.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
187
References
1. F.Е. Shubert, Light Emitting Diodes, Fizmatlit
Publ., Moscow, 2008 (in Russian).
2. A. Berg, P. Din, Light Emitting Diodes, Mir Publ.,
Moscow, 1979 (in Russian).
3. V.V. Evstropov, Yu.V. Zhiliayev, M. Dzhumaeva,
N. Nazarov, Tunnel-excess current in nondegenerated
barrier p-n and m-s silicon-containing ІІІ-V compound
semiconductor structures // Fizika i tekhnika polu-
provodnikov, 31(2), p. 152-158 (1997), in Russian.
4. V.V. Evstropov, Yu.V. Zhiliayev, M. Dzhumaeva, N.
Nazarov, A.A. Sitnikova, L.M. Fedorov, Dislocation
origin and a model of the excessive tunnel current in
GaP p-n structure // Fizika i tekhnika poluprovodnikov,
34(11), p. 1357-1368 (2000), in Russian.
5. D.V. Lang, L.C. Kimerling, Observation of a
thermal defect annealing in GaP // Appl. Phys. Lett.
28, p. 248 (1976).
6. A. Borsakovskyj, O. Gontaruk, V. Kochkin,
P. Litovchenko, V. Opilat, I. Petrenko,
V Tartachnyk, Radiation influence on
characteristics of GaP light emitting diodes //
Functional Materials, 16, p. 313-318 (2009).
7. A.V. Gomonnai, D.B. Goyer, O.O. Goushcha,
Yu.M. Azhniuk, I.G. Megela, M. Kranjcec,
Radiative recombination in electron-irradiated GaP
crystals // J. Optoelectron. Adv. Mater. 5(3),
p. 641-646 (2003).
8. T. Endo, T. Nichimura, K. Nakakuki, M. Kitamura,
K. Sugijama, DLTS study for energy-broadening of
the defect level on introducing radiation damage in
GaP // Jpn. J. Appl. Phys. 27(11), p. 2107-2112
(1988).
9. T. Endo, Yu. Hirosaki, E. Uchida, H. Miyake,
K. Sugiyama, Deep levels in electron-irradiated
GaP at 10 MeV // Jpn. J. Appl. Phys. 28(10),
p. 1864-1870 (1989).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 2. P. 184-187.
PACS 29.40.-n, 85.30.-z, 85.60.Dw
Influence of complex defects on electrophysical properties
of GaP light emitting diodes
O. Konoreva1, E. Malyj1, S. Mamykin2,*, I. Petrenko1, M. Pinkovska1, V. Tartachnyk1
1Institute for Nuclear Researches, NAS of Ukraine,
47, prospect Nauky, 03028 Kyiv, Ukraine
2V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine,
41, prospect Nauky, 03028 Kyiv, Ukraine
*Corresponding author phone: +38(044)-525-37-49; e-mail: myrglory@yahoo.com
Abstract. In order to estimate the role of complex defects on GaP light emitting diodes (LED) operation, luminescent and electrical characteristics of GaP LEDs irradiated with reactor neutrons have been studied. It has been stated that nonradiative levels of radiation defects affect electroluminescence quenching. From the analysis of the tunnel current, the density of dislocations in the depleted part of the p–n junction was obtained. Neutron induced disorder regions do not change the tunnel component of the direct current of red diodes, increasing the dislocation density, because the carrier flow along the “tunnel shunts” is blocked.
Keywords: gallium phosphide, light emitting diode, defect, luminescence and quantum yield.
Manuscript received 21.01.14; revised version received 12.05.14; accepted for publication 12.06.14; published online 30.06.14.
1. Introduction
The external quantum yield of light emitting diode (LED), which determines its effectiveness, depends on three factors: (Е = (і (l (o, where (і is the coefficient of minority carrier injection, (l – effectiveness of light generation and (о – coefficient of light output. The first and second multipliers characterize the quality of the crystal and p–n junction and are usually combined as the internal quantum yield (I = (і (l [1].
It is more difficult to control a commercial device than a separate crystal, especially if complex defects such as dislocations, radiation induced defects and other ones are available and dominate in device properties. One should know that defects of “dark line” and “dark spot” types, responsible for degradation processes in GaP LEDs, are caused by the accumulation of dislocation networks [2].
While creating the p–n junction in LEDs, layers of different conductivity are deposited epitaxially on substrate. Due to the interface between these two films, defects are accumulated within the depleted region of transition at a distance of 2-3 diffusion lengths from this interface. It negatively affects the value of the internal quantum yield.
The situation is still worsening due to the growth of dislocations out of the substrate surface, which is previously polished and possesses a great amount of line-type defects (( > 106 cm–2). In order to eliminate the influence of the substrate surface, it is unreasonable to increase the n-film thickness, because self-absorption of photons will increase.
Therefore, we hope that the study of behavior of dislocations in the transition region will help to predict the LED performance.
The authors of the papers [3, 4] showed the possibility of appearance of the excess direct tunnel current not only in degenerate p–n–n junctions and heterostructures. It turns out that the model of “dislocation shunt”, which describes interdefect tunneling of carriers in the space charge region, can be applied to the homojunction where the tunneling process occurs along the dislocation line.
Based on the conclusions obtained in [3, 4], one can appreciate the density of dislocations in the p–n junction and identify the impact of extreme external factors (including also fast particle irradiation – in this case) on interdislocation tunneling of carriers.
We have presented the results of the study of electroluminescence spectra and electrophysical characteristics of GaP LEDs irradiated with fast reactor neutrons. Current-voltage characteristics of initial diodes and those with radiation defects have been analyzed using the method proposed in the paper [4], and the dislocation influence has been estimated as well.
2. Experimental
We studied green and red industrial LEDs made using double solid epitaxial methods. Green LEDs were doped with nitrogen atoms, red – with zinc and oxygen, simultaneously. The electron concentration was equal to
3
17
cm
10
2
-
×
, and that of holes –
(
)
3
16
cm
10
5
4
-
×
-
. The n-GaP substrate was made using the Czochralsky method with the carrier concentration
(
)
3
17
cm
10
7
5
-
×
-
. The sample dimensions were 1×1 mm. The diodes were irradiated with fast neutrons in reactor at room temperature. Current-voltage characteristics were measured manually and by the automatic system within the range
A
10
...
1
9
-
for current and 1 to 30 V – for voltage at temperatures ranging from 77 up to 300 K.
Electroluminescence spectra were measured by a spectrometer BLK-C F1000-VIS NIR-1 (StellarNet Inc) for 190…850 nm intervals within the same temperature range 77 to 300 K.
3. Result and discussion
The electroluminescence spectra of green GaP LEDs measured at room and nitrogen temperatures are given in Fig. 1. As one can see, the low temperature spectrum possesses a fine structure due to izoelectron nitrogen impurity. In the near-edge part of the spectrum, there is a line associated with exciton bound to nitrogen atom. Its intensity is significantly weaker than luminosity of exciton bound to the pair of NNi centers due to the lower binding energy and effect of self-absorption. When the sample temperature increases up to 300 K, the fine structure of the spectrum disappears.
Fig. 1. Electroluminescence spectrum of GaP LED at 300 and 77 K.
The main emission band is related with the pair NN1. It has E = 2.22 eV and LA line as phonon duplication.
Irradiation of GaP LED with fast reactor neutrons causes a monotonic intensity drop of all the lines, and the luminosity of exciton bound to the isolated nitrogen atom is the most sensitive region of the spectrum to introduction of radiation defects.
It was stated in [5] and confirmed later by us and other authors [6-9] that the radiationless level of radiation defects is a reason for electroluminescence quenching.
It should be said that impurity levels existing in the forbidden band of non-irradiated diode can also be the centers of nonradiative recombination and reduce the internal quantum yield.
It was found [2] that the low value of the internal quantum yield of irradiated GaP LEDs was due to deep levels caused mainly by dislocations in the
n
p
-
junction, the thickness of which was of the order of the diffusion length inherent to minority carriers.
Excess tunneling through the depleted region of the diode is a component of the injection current and can exist not only in the degenerate structures. Even at base moderate doping of the p–n junction (order (
3
17
cm
10
-
), this opportunity may be provided by hopping-like tunneling through the space charge region [3, 4].
In the dislocation shunt model, the exponential part of the current-voltage characteristics is described as follows:
÷
ø
ö
ç
è
æ
-
e
=
1
exp
0
eV
I
I
.
Here, unlike the Shockley formula, І0 is the function not only of diffusion and electric constants of the base:
÷
÷
ø
ö
ç
ç
è
æ
e
-
rn
=
c
eV
e
I
exp
D
0
,
where ( is the dislocation density, ( – characteristic energy, (D – Debye frequency, and е – electron charge.
The contact potential difference Vc (like to the classical model) may be given in the form of
,
ln
ln
ln
ln
ln
ln
2
ï
þ
ï
ý
ü
ï
î
ï
í
ì
+
-
=
ú
ú
ú
ú
û
ù
ê
ê
ê
ê
ë
é
-
=
=
ú
ú
û
ù
ê
ê
ë
é
=
ú
û
ù
ê
ë
é
+
=
p
V
n
C
g
g
V
C
n
p
i
n
p
i
n
i
p
c
p
N
n
N
e
kT
e
E
kT
E
e
N
N
n
p
e
kT
n
n
p
e
kT
n
n
n
p
e
kT
V
where Еg is the band gap; NC, NV are densities of states in the appropriated conduction and valence bands; nn, pp are concentrations of electrons and holes, respectively.
Considering the GaP temperature dependence of the band gap Eg = Eg(0) – (T, where ( is a constant, one can define the ( parameter and dislocation density:
e
÷
÷
ø
ö
ç
ç
è
æ
n
=
r
g
g
kT
V
C
p
n
E
N
N
p
n
e
I
exp
D
0
.
GaP current-voltage characteristics of green (active region is doped with nitrogen), red (doped with both zinc and oxygen) and the same diode irradiated with fast reactor neutrons (E = 1 MeV, F =
2
16
cm
10
-
) are given in Fig. 2.
Fig. 2. Current-voltage characteristics of GaP LED diode: irradiated with fast reactor neutrons (1); initial red (2) and green (3) diodes.
In the latter case, the neutron dose was so high that the diode stopped emitting even at significant levels of injection (I = 50…60 mA). By extrapolating the exponential plot of the current-voltage dependence on the zero displacement, it is possible to obtain І0, where ( is the curve slope. Measurements carried out within the range 77…300 K showed that both the parameters did not practically depend on temperature. Considering that NV = NC =
3
18
cm
10
8
-
×
and n ( p (
3
17
cm
10
-
, corresponding to the mean value of the carrier concentration in the base of the diodes of AL-102 BM series, the average dislocation density in green GaP(N) is equal to (D =
2
10
cm
10
5
.
7
-
×
, in red GaP (Zn-O) (D =
2
8
cm
10
4
-
×
.
After neutron irradiation of red diodes, (D is equal to
2
8
cm
10
4
.
4
-
×
.
So, it is obvious that in red diodes neutrons do not appreciably affect the density of linear defects – dislocations, despite the fact that thermal wedges and associated deformation fields or Brinkman peaks of displacements appear in irradiated objects.
It is also obvious that under neutron irradiation the crystal structure becomes so disordered that tunnel jumps, occuring in non-irradiated crystal along the dislocation tubes, become impossible due to fractures of dislocation lines. An additional increase of dislocation densities in the periphery areas of disordered regions does not affect the value of the tunnel component of the direct current. “Dislocation shunt” does not work within the space charge region.
4. Conclusions
Main lines of electroluminescence spectra of green GaP(N) LEDs have been identified at different temperatures. At 77 K, the thin structure was discovered with the peak associated with exciton bound to separate nitrogen atom. Its intensity is significantly weaker than that of exciton bound to the pair of NN centers due to the lower binding energy and effect of self-luminosity. The structure vanishes when temperature increases up to 300 K. Neutron irradiation causes monotonic quenching of all the components in the electroluminescence spectrum.
The model of dislocation tunneling makes it possible to assess the density of dislocations in the depleted part of the
n
p
-
junction. This value (D is close to
2
10
cm
10
5
.
7
-
×
in green GaP(N) and in red GaP (Zn-O) –
2
8
cm
10
4
-
×
. Neutron irradiation does not significantly affect (D of red diodes.
It has been suggested that the disorder regions induced with neutrons are able to block the current flow along the “tunnel shunts”.
The authors thank to M. Lytovchenko for his help in carrying out the experiment.
References
1. F.Е. Shubert, Light Emitting Diodes, Fizmatlit Publ., Moscow, 2008 (in Russian).
2. A. Berg, P. Din, Light Emitting Diodes, Mir Publ., Moscow, 1979 (in Russian).
3. V.V. Evstropov, Yu.V. Zhiliayev, M. Dzhumaeva, N. Nazarov, Tunnel-excess current in nondegenerated barrier p-n and m-s silicon-containing ІІІ-V compound semiconductor structures // Fizika i tekhnika poluprovodnikov, 31(2), p. 152-158 (1997), in Russian.
4. V.V. Evstropov, Yu.V. Zhiliayev, M. Dzhumaeva, N. Nazarov, A.A. Sitnikova, L.M. Fedorov, Dislocation origin and a model of the excessive tunnel current in GaP p-n structure // Fizika i tekhnika poluprovodnikov, 34(11), p. 1357-1368 (2000), in Russian.
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6.
A. Borsakovskyj, O. Gontaruk, V. Kochkin, P. Litovchenko, V. Opilat, I. Petrenko, V Tartachnyk, Radiation influence on characteristics of GaP light emitting diodes // Functional Materials, 16, p. 313-318 (2009).
7. A.V. Gomonnai, D.B. Goyer, O.O. Goushcha, Yu.M. Azhniuk, I.G. Megela, M. Kranjcec, Radiative recombination in electron-irradiated GaP crystals // J. Optoelectron. Adv. Mater. 5(3), p. 641-646 (2003).
8. T. Endo, T. Nichimura, K. Nakakuki, M. Kitamura, K. Sugijama, DLTS study for energy-broadening of the defect level on introducing radiation damage in GaP // Jpn. J. Appl. Phys. 27(11), p. 2107-2112 (1988).
9. T. Endo, Yu. Hirosaki, E. Uchida, H. Miyake, K. Sugiyama, Deep levels in electron-irradiated GaP at 10 MeV // Jpn. J. Appl. Phys. 28(10), p. 1864-1870 (1989).
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
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