Peculiarities of neutron irradiation influence on GaP light-emitting structures
GaP LEDs irradiated by reactor neutrons were studied by optical and electrical methods. The observed emission intensity degradation is related with two factors: 1) radiation fields that destroy bond excitons and 2) decrease in the free charge carrier concentration, which is caused by their captur...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2009
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| Zitieren: | Peculiarities of neutron irradiation influence on GaP light-emitting structures / P. Litovchenko, A. Litovchenko, O. Konoreva, V. Opilat, M. Pinkovska, V. Tartachnyk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2009. — Т. 12, № 3. — С. 276-279. — Бібліогр.: 8 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-1188742025-06-03T16:26:27Z Peculiarities of neutron irradiation influence on GaP light-emitting structures Litovchenko, P. Litovchenko, A. Konoreva, O. Opilat, V. Pinkovska, M. Tartachnyk, V. GaP LEDs irradiated by reactor neutrons were studied by optical and electrical methods. The observed emission intensity degradation is related with two factors: 1) radiation fields that destroy bond excitons and 2) decrease in the free charge carrier concentration, which is caused by their capture by radiation defects. Study of currentvoltage characteristics at 77 K by highly precession methods has revealed the appearance of N-shaped negative differential region caused by carrier tunneling onto deep levels in quantum wells, which might exist in initial and irradiated p-n structures. In some cases, improvement of current-voltage characteristics after neutron irradiation is observed. An assumption is made about the radiation-stimulated origin of this effect. 2009 Article Peculiarities of neutron irradiation influence on GaP light-emitting structures / P. Litovchenko, A. Litovchenko, O. Konoreva, V. Opilat, M. Pinkovska, V. Tartachnyk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2009. — Т. 12, № 3. — С. 276-279. — Бібліогр.: 8 назв. — англ. 1560-8034 PACS 29.40.-n, 85.30.-z, 85.60.Dw https://nasplib.isofts.kiev.ua/handle/123456789/118874 en Semiconductor Physics Quantum Electronics & Optoelectronics application/pdf Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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English |
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GaP LEDs irradiated by reactor neutrons were studied by optical and electrical
methods. The observed emission intensity degradation is related with two factors:
1) radiation fields that destroy bond excitons and 2) decrease in the free charge carrier
concentration, which is caused by their capture by radiation defects. Study of currentvoltage
characteristics at 77 K by highly precession methods has revealed the appearance
of N-shaped negative differential region caused by carrier tunneling onto deep levels in
quantum wells, which might exist in initial and irradiated p-n structures. In some cases,
improvement of current-voltage characteristics after neutron irradiation is observed. An
assumption is made about the radiation-stimulated origin of this effect. |
| format |
Article |
| author |
Litovchenko, P. Litovchenko, A. Konoreva, O. Opilat, V. Pinkovska, M. Tartachnyk, V. |
| spellingShingle |
Litovchenko, P. Litovchenko, A. Konoreva, O. Opilat, V. Pinkovska, M. Tartachnyk, V. Peculiarities of neutron irradiation influence on GaP light-emitting structures Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Litovchenko, P. Litovchenko, A. Konoreva, O. Opilat, V. Pinkovska, M. Tartachnyk, V. |
| author_sort |
Litovchenko, P. |
| title |
Peculiarities of neutron irradiation influence on GaP light-emitting structures |
| title_short |
Peculiarities of neutron irradiation influence on GaP light-emitting structures |
| title_full |
Peculiarities of neutron irradiation influence on GaP light-emitting structures |
| title_fullStr |
Peculiarities of neutron irradiation influence on GaP light-emitting structures |
| title_full_unstemmed |
Peculiarities of neutron irradiation influence on GaP light-emitting structures |
| title_sort |
peculiarities of neutron irradiation influence on gap light-emitting structures |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2009 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/118874 |
| citation_txt |
Peculiarities of neutron irradiation influence on GaP light-emitting structures / P. Litovchenko, A. Litovchenko, O. Konoreva, V. Opilat, M. Pinkovska, V. Tartachnyk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2009. — Т. 12, № 3. — С. 276-279. — Бібліогр.: 8 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
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| first_indexed |
2025-12-02T05:37:11Z |
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2025-12-02T05:37:11Z |
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| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 3. P. 276-279.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
276
PACS 29.40.-n, 85.30.-z, 85.60.Dw
Peculiarities of neutron irradiation influence
on GaP light-emitting structures
P. Litovchenko, A. Litovchenko, O. Konoreva, V. Opilat*, M. Pinkovska, V. Tartachnyk
Institute for Nuclear Researches, NAS of Ukraine, 47, prospect Nauky, 03028 Kyiv, Ukraine
*M. Drahomanov National Pedagogical University, 9, Pirohova str., 03023 Kyiv, Ukraine
Corresponding author: phone+38(044)-525-39-97, +38(044)-525-37-49; e-mail: okskon@meta.ua
Abstract. GaP LEDs irradiated by reactor neutrons were studied by optical and electrical
methods. The observed emission intensity degradation is related with two factors:
1) radiation fields that destroy bond excitons and 2) decrease in the free charge carrier
concentration, which is caused by their capture by radiation defects. Study of current-
voltage characteristics at 77 K by highly precession methods has revealed the appearance
of N-shaped negative differential region caused by carrier tunneling onto deep levels in
quantum wells, which might exist in initial and irradiated p-n structures. In some cases,
improvement of current-voltage characteristics after neutron irradiation is observed. An
assumption is made about the radiation-stimulated origin of this effect.
Keywords: GaP LEDs, irradiation, emission degradation, negative resistance,
oscillation.
Manuscript received 15.04.09; accepted for publication 14.05.09; published online 29.05.09.
1. Introduction
Light emitting diodes (LEDs) are widely used in
computing systems, contemporary high frequency
intercommunication, monitoring, diagnostics domestic
devices due to small size, simplicity and low cost.
Despite technology advantages, the quantum yield of
diodes is not stable enough and decreases during diode
operation [1, 2]. The radiation stability increase is the
issue of the day for all LED types. Later, the influence of
irradiation on GaP LEDs was studied in [3-5]. Thermal
stability of radiation defects in GaP LEDs is not clear up
to date. The radiation trap parameters and the thermal
stability range of radiation induced defects can be
obtained by analysis of electrical characteristics of LEDs
after irradiation. Some features of current-voltage
characteristics for irradiated LEDs were presented in our
previous study [6]. In the abovementioned paper, the
electrical and optical properties of CZ GaP p-n junctions
used as substrates for LEDs irradiated by reactor
neutrons were studied and compared with the electron-
irradiated ones.
2. Experiment and results
The studied GaP light diodes were processed by double
liquid epitaxy. Current-voltage characteristics (C-V) of
p-n structures were measured at nitrogen and room
temperatures. The thin structure of C-V of p-n junction
has been measured by special technique that allows to
change precisely current or voltage steps, which makes it
possible to do measurements nearly momentary.
Samples were characterized by DLTS and emission
spectra measurements. The structures were irradiated by
reactor neutrons at 50 C and electrons (E = 2 MeV).
Introduction of the radiation defects into GaP LEDs
causes decrease of the emission intensity I (Fig. 1), and
can be expressed as I = I0 exp(–kΦ). The average value
of the damage coefficient for reactor neutrons
( E = 1 MeV) obtained from the abovementioned
expression is kn1 = 1.1810-13 cm2 for the fluence range
Φ = (0…9)1012 cm-2, and kn2 = 0.59 10-13 cm2 – for Φ =
91012 – 1014 cm-2. The average value of the damage
coefficient ke is (9.2…4.5)10-16 cm2 for electron fluences
(0…2)1015 cm-2 and 21015 – 41016 cm-2, respectively.
The comparison of neutron and electron cases gives for
the initial irradiation fluences the ratio kn1/ ke1 ≈ 102.
Thus, the reactor neutron radiation damage is much
higher than that of the electron one and can be explained
by the complex defect formation. Therefore, thermal
stability of the neutron induced radiation defects is high.
As seen from Fig. 2, the second stage of annealing the
radiation defects, i.e., annealing of the disorder regions,
occurs at T > 500 C, while point defects (VGa and VP,
induced by reactor gamma-irradiation) are annealled at
100 to 200 C.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 3. P. 276-279.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
277
Fig. 1. Intensity emission drop as the function of radiation
with: 1 – neutrons, n = 11.81012 сm-2; 2 – electrons,
n = 2.61014 сm-2.
Fig. 2. Annealing of the concentration n (1), conductivity σ (2)
and mobility (3) of GaP LEDs irradiated with neutrons
Ф = 1016 сm-2.
After electron irradiation, we observed five deep
levels in GaP forbidden gap appearing with the
introduction rate 6.2 cm-1 measured by DLTS technique.
This value agrees well with the carrier removal rate.
Thus, each induced defect captures one free carrier.
It can be suggested that radiation defects are
monovalent. The concentration of deep levels with the
energy E = 0.79 eV increases.
In neutron-irradiated samples (Φ = 31014 cm-2)
only 0.2-0.7 eV wide band appears with the mean
concentration of induced defects 51015 cm-3. After
neutron irradiation, the concentration of deep levels with
the energy E = 0.79 eV also presented in GaP forbidden
gap of non-irradiated diodes increases. The main
changes in DLTS spectra of neutron irradiated GaP
diodes are observed after 400 C annealing. The
concentration of traps with the energy E = 0.2-0.7 eV
decreases down to 31014 cm-3 and new traps with the
concentration 61015 cm-3 and energy E = 0.71 eV
appear.
The main peculiarities of the GaP LEDs are in
appearance of current instabilities in the region of
negative resistance in C-V characteristics at 100-77 K.
These oscillations were observed earlier [6] and related
with filling and depletion of deep levels.
Detailed analysis of C-V characteristics measured
in voltage-generator mode at the nitrogen temperature
has also shown N-type irregularities both in forward and
reverse characteristics. In some samples, especially in
the irradiated ones, these characteristics might be
divided into separate curves, which follow one by one.
Neutron irradiation leads to appearance of a thin
structure in the N-type region of direct C-V
characteristics and the current oscillation amplitude
increases (Fig. 3).
The similar results are observed for the reverse C-V
curve, and nature of the current oscillations differs after
annealing (Fig. 4). The Irev(V) curve demonstrates the
deep minimal current. This value decreases with
repetition of these measurements (Fig. 5). The N-shaped
anomalies in both parts of current-voltage characteristics
can be explained by current tunneling into large-scale
defects of quantum well-type [7]. They are present in
initial samples and irradiation may influence on it. The
electric field 106 V/cm has been applied to the p-n
transition region. This value is enough to stimulate
tunneling currents under conditions when the level of the
defect quantum well as caused by the band shift is
opposite as compared to that of the conductive/valence
band edge. The change of the minimal current in reverse
C-V characteristics after the repeating measurements
(Fig. 5) confirmed this hypothesis, each followed
current-voltage measure causes changes in the level
filling of quantum wells.
Fig. 3. Current-voltage characteristics of GaP,Zn:O measured in
voltage-generator mode at 77 K: 1 – initial, 2 – Ф =
4.51016 neutrons/сm2, 3 – annealled 600 С.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 3. P. 276-279.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
278
Fig. 4. Reverse current-voltage characteristics of GaP,Zn:O
annealled at temperatures: 1 – initial, 2 – 80, 3 – 110, 4 –
130 С.
Fig. 5. Reverse current-voltage characteristics of GaP LEDs
when repeating the measurements.
Improvement of electrical characteristics obvious
in neutron-irradiated (Φ ≤ 1014 cm-2) GaP LEDs at room
temperatures is expressed by direct current increase,
while reverse current and oscillation amplitudes in N-
and S-shaped regions decreases. The differential
resistance decreases at low direct currents and biases,
and the point of intersection of forward C-V
characteristics for non-irradiated and irradiated diodes
goes down with the neutron dose increase (Fig. 6).
3. Discussion
The irradiation introduces deep levels into the GaP
forbidden gap, which may capture the majority current
carriers. The Fermi level shifts to the middle of
forbidden gap and reaches the value Eg/2 with the
neutron fluence increase. But conversion of the
conductivity type is not observed even for high fluences.
Fig. 6. Improvement of current-voltage characteristics of GaP
LEDs after neutron irradiation: 1 – initial, 2 – first fluence, 3 –
second fluence.
The emission characteristics are very sensitive to
radiation, so the effect is related with the annihilation of
the bound excitons. The emission intensity decreases at
low neutron fluences. The changes in electrical
characteristics are not constant. This emission
degradation depends exponentially on the fluence.
Radiation influences on the radiative centers and
destroys excitons. The ratio of radiation damage
coefficients for neutrons and electrons at the beginning
of irradiation (~102) confirms this statement. The sharp
bend in Fig. 1 divides the experimental curve by two
parts: the region of low fluences, where excitons are
destroyed by radiation, and the high fluence region,
where, apparently, this effect is accompanied by the
decrease of the majority carriers’ concentration in GaP.
The emission intensity degradation was evaluated
using DLTS measurement results. The comparison of
annealing temperatures for traps obtained by DLTS
measurements as well as annealing stages of VGa and VP
in GaP shows that the level E = 0.6 eV belongs to VGa.
Other levels are related with VGa complex defects. The
wide band 0.2-0.7 eV in DLTS spectra is the result of
superposition of nearly located levels in neutron
irradiated diodes. We suppose that this band is formed
by defects of disordered regions. The increase in the
concentration of the level E = 0.71 eV at high annealing
temperatures is the result of the beginning of complex
defect decay. The disordered regions dissociate for
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 3. P. 276-279.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
279
components such as complexes of radiation defect and
impurity/defect associations, for example.
Improvement of diode electrical characteristics
after neutron irradiation has to be studied. It is possible
to assume only that radiation-stimulated transformation
occurs [7]. The impurity diffusion in the depletion
region becomes stronger under high ionization levels
and under sufficient electrical p-n junction field.
4. Conclusion
1. Our study of emission characteristics of GaP LEDs
irradiated by reactor neutrons and electrons has
confirmed that destructive influence of neutrons is
higher than electrons and is related with complex
defect formation. Emission intensity degradation of
neutron-irradiated diodes at medium fluences is
related with two factors: the radiation that destroys
the bound excitons and the decrease of free carriers
due to their capture by radiation defects.
2. From DLTS spectra parameters of same traps with
the energies E = 0.25, 0.29, 0.33, 0.55, and 0.60 eV
were revealed after electron irradiation. The mean
trap incorporation rate is 6.2 cm-1. In neutron-
irradiated samples (Φ = 31014 cm-2), the only 0.2-
0.7 eV wide band appears with the mean
concentration of induced defects 51015 cm-3.
3. The region of N-shaped NDR was observed at 77 K
and caused by the carrier tunneling in deep levels
of quantum wells, which are in non-irradiated and
irradiated p-n structures.
4. Improvement of GaP diode current-voltage
characteristics after neutron irradiation is observed.
An assumption is made about the radiation-
stimulated nature of this effect.
References
1. A. Berg, P. Din. Light Emitting Diodes. Mir Publ.,
Moscow, 1979 (in Russian).
2. R.I. Hartman, B. Schwartz, M. Kuhn, Degradation
and passivation of GaP light-emitting diodes //
Appl. Phys. Lett. 18, p. 304-306 (1971).
3. A. Polity, T.N. Abgargan, R. Krause-Rohberg,
Defects in electron irradiated GaP studied by
positron lifetime spectroscopy // J. Appl. Phys. A
60, p. 541-544 (1995).
4. T. Kawakubo and M. Okada, Electrical and optical
properties of neutron-irradiated GaP crystals // J.
Appl. Phys. A 67, p. 3111-3114 (1990).
5. A.H. Johnson, B.G. Rax, L.E. Selva, and C.E. Bar-
nes, Proton degradation of light-emitting diodes //
IEEE Trans. Nucl. Sci. 46, p. 1781-1789 (1999).
6. P. Litovchenko, D. Bisello, A. Litovchenko,
S. Kanevskyj, V. Opilat, M. Pinkovska,
V. Tartachnyk, R. Rando, P. Giubilato, Some
features of current-voltage characteristics of
irradiated GaP light diodes // Nucl. Instrum. Meth.
A 552, p. 93-97 (2005).
7. V.E. Kudrishov, K.G. Zolin, A.N. Turkin,
A.E. Yunovich, A.N. Kovalev, F.I. Maniakhin,
Tunnelling in light-emitting diodes based on
InGaN/AlGaN/GaN heterostructures with quantum
wells // Fizika i tekhnika poluprovodnikov 31,
p. 1304-1309 (1997) (in Russian).
8. O.Yu. Borkovskaya, N.L. Dmytruk, V.G. Lytov-
henko, O.N. Mishchuk, On the model of the effect
of radiation-stimulated ordering in semiconductors
A3B5 // Fizika i tekhnika poluprovodnikov 23,
No. 2, p. 207-212 (1989) (in Russian).
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