Low doses effect in GaP light-emitting diodes
The paper is devoted to the electrophysical characteristics study of serial red and green GaP light-emitting diodes (LEDs) irradiated with low α-particles doses (Φ ≤ 10¹² cm⁻²). It was stated that radiation features of p-n-junction and its capacitance change in dependence on temperature. The capacit...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2016
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| Цитувати: | Low doses effect in GaP light-emitting diodes / O.M. Hontaruk, O.V. Konoreva, Ye.V. Malyi, I.V. Petrenko, M.B. Pinkovska, O.I. Radkevych, V.P. Tartachnyk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2016. — Т. 19, № 2. — С. 183-187. — Бібліогр.: 13 назв. — англ. |
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irk-123456789-1215592017-06-15T03:05:33Z Low doses effect in GaP light-emitting diodes Hontaruk, O.M. Konoreva, O.V. Malyi, Ye.V. Petrenko, I.V. Pinkovska, M.B. Radkevych, O.I. Tartachnyk, V.P. The paper is devoted to the electrophysical characteristics study of serial red and green GaP light-emitting diodes (LEDs) irradiated with low α-particles doses (Φ ≤ 10¹² cm⁻²). It was stated that radiation features of p-n-junction and its capacitance change in dependence on temperature. The capacitance grows at 300 K, and drops at 77 K. At the same time, a direct branch of current-voltage characteristics shifts into the lower voltage direction, and appropriative barrier potential reduction value from 6.5 down to 3.5 eV is observed. The effects are caused by radiation defects, charge state of which depends on the Fermi level in GaP. The assumption has been made about high ionization level role in the sulfur impurity transition process into electrically active donor position. 2016 Article Low doses effect in GaP light-emitting diodes / O.M. Hontaruk, O.V. Konoreva, Ye.V. Malyi, I.V. Petrenko, M.B. Pinkovska, O.I. Radkevych, V.P. Tartachnyk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2016. — Т. 19, № 2. — С. 183-187. — Бібліогр.: 13 назв. — англ. 1560-8034 DOI: 10.15407/spqeo19.02.183 PACS 29.40.-n, 85.30.-z, 85.60.Dw http://dspace.nbuv.gov.ua/handle/123456789/121559 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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The paper is devoted to the electrophysical characteristics study of serial red and green GaP light-emitting diodes (LEDs) irradiated with low α-particles doses (Φ ≤ 10¹² cm⁻²). It was stated that radiation features of p-n-junction and its capacitance change in dependence on temperature. The capacitance grows at 300 K, and drops at 77 K. At the same time, a direct branch of current-voltage characteristics shifts into the lower voltage direction, and appropriative barrier potential reduction value from 6.5 down to 3.5 eV is observed. The effects are caused by radiation defects, charge state of which depends on the Fermi level in GaP. The assumption has been made about high ionization level role in the sulfur impurity transition process into electrically active donor position. |
| format |
Article |
| author |
Hontaruk, O.M. Konoreva, O.V. Malyi, Ye.V. Petrenko, I.V. Pinkovska, M.B. Radkevych, O.I. Tartachnyk, V.P. |
| spellingShingle |
Hontaruk, O.M. Konoreva, O.V. Malyi, Ye.V. Petrenko, I.V. Pinkovska, M.B. Radkevych, O.I. Tartachnyk, V.P. Low doses effect in GaP light-emitting diodes Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Hontaruk, O.M. Konoreva, O.V. Malyi, Ye.V. Petrenko, I.V. Pinkovska, M.B. Radkevych, O.I. Tartachnyk, V.P. |
| author_sort |
Hontaruk, O.M. |
| title |
Low doses effect in GaP light-emitting diodes |
| title_short |
Low doses effect in GaP light-emitting diodes |
| title_full |
Low doses effect in GaP light-emitting diodes |
| title_fullStr |
Low doses effect in GaP light-emitting diodes |
| title_full_unstemmed |
Low doses effect in GaP light-emitting diodes |
| title_sort |
low doses effect in gap light-emitting diodes |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2016 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/121559 |
| citation_txt |
Low doses effect in GaP light-emitting diodes / O.M. Hontaruk, O.V. Konoreva, Ye.V. Malyi, I.V. Petrenko, M.B. Pinkovska, O.I. Radkevych, V.P. Tartachnyk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2016. — Т. 19, № 2. — С. 183-187. — Бібліогр.: 13 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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2025-07-08T20:07:24Z |
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| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 2. P. 183-187.
doi: 10.15407/spqeo19.02.183
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
183
PACS 29.40.-n, 85.30.-z, 85.60.Dw
Low doses effect in GaP light-emitting diodes
O.M. Hontaruk1, O.V. Konoreva1, Ye.V. Malyi1, I.V. Petrenko1, M.B. Pinkovska1,
O.I. Radkevych2, V.P. Tartachnyk1
1Institute for Nuclear Researches, NAS of Ukraine, 47, prospect Nauky, 03028 Kyiv, Ukraine
2SE “RI of Microdevices” STC “Institute for Single Crystals”, NAS of Ukraine,
3, Pivnichno-Syretska str., 04136 Kyiv, Ukraine
Corresponding author phone: +38(044)-525-37-49; e-mail: evgen.malyj@gmail.com
Abstract. The paper is devoted to the electrophysical characteristics study of serial red
and green GaP light-emitting diodes (LEDs) irradiated with low α-particles doses (Φ ≤
1012 cm–2). It was stated that radiation features of p-n-junction and its capacitance change
in dependence on temperature. The capacitance grows at 300 K, and drops at 77 K. At
the same time, a direct branch of current-voltage characteristics shifts into the lower
voltage direction, and appropriative barrier potential reduction value from 6.5 down to
3.5 eV is observed. The effects are caused by radiation defects, charge state of which
depends on the Fermi level in GaP. The assumption has been made about high ionization
level role in the sulfur impurity transition process into electrically active donor position.
Keywords: gallium phosphide, GaP, LEDs, CVC, α-particles, irradiation, low doses,
capacitance.
Manuscript received 14.12.15; revised version received 05.04.16; accepted for
publication 08.06.16; published online 06.07.16.
1. Introduction
It is known that radiation defects induced by fast
particles in light-emitting diodes (LEDs) causes
appearing of deep energy levels in semiconductor band
gap. They capture charge carriers and affect the p-n-
junction parameters. Irradiation leads to p-n-junction
capacitance reduction, the differential resistance growth,
potential barrier value decrease among semiconductor
regions with different conductivity types and base
resistance increase.
However, this situation is not always realized in
practice. Despite numbers of publications devoted to this
problem [1-6], one can hardly consider sufficient
information amount needed to predict behavior of the
devices in extreme conditions. This is especially true
concerning the early irradiation stages, the so-called
“low doses effect” that is observed at crystal electron
subsystem excitation high levels.
In this paper, the results of the α-particles effect
researches on the electrical gallium phosphide LEDs
characteristics and diode behavior peculiarities at initial
irradiation stages are presented. It should be also noted
that one can use “positive” effect observed at low doses
to correct performances of the industrial diode
structures.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 2. P. 183-187.
doi: 10.15407/spqeo19.02.183
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
184
2. Experimental
Measurements were carried out using the red and green
LEDs obtained by double liquid epitaxy of a solution-
melt limited volume on the substrate (111) grown by
Czochralski method. The substrate thickness was
approximately 200 μm; the epitaxial films thicknesses
were dn = 50…60 μm, dp = 20…30 μm. The electron
conductivity of substrate film and n-type film were
obtained using Te doping; the hole conductivity of p-
type film was reached using Zn. Nitrogen was green
emission activator, and Zn-O complex was red emission
activator. The p-doped region level was nearly 5 times
higher than the main dopant concentration in p-n-
junction n-region. Current-voltage (CVC) and
capacitance-voltage characteristics of the diodes were
measured at 77 and 300 K. Samples were irradiated with
α-particles in U-120 cyclotron at room temperature, Eα =
27 MeV; fluence was Ф ≤ 1012 cm–2.
It is possible to estimate the α-particle penetration
depth Rα with the energy E in GaP crystal by using the
known ratio:
ρ
= −
α
AER 2
3
410 , (1)
where E is a particle’s energy, ρ – material density, A –
substance atomic weight.
Since GaP is a binary compound, evaluation of the
penetration depth can be done in two ways based on the
average GaP atomic weight A ≈ 50 or separately for Ga
and P atoms, and then by determination of their average.
The first method gives the value Rα = 253 μm; the
second is 292 μm; the values are quite close to each
other. The total sample thickness was d ≤ 290 μm.
Therefore, for given small epitaxial films thickness one
can consider that radiation defects are uniformly
distributed inside the p-n-junction.
3. Results and discussion
Applying an external voltage to the diode structure leads
to changes in the space charge value, which manifests
itself in a changing capacitance. It is known that
irradiation of GaP diodes with fast electrons
(E = 1 MeV) in moderate and high doses leads to a
decrease in the capacitance of p-n-junction [7] due to
deep levels of radiation defects. The main reason for the
destructive radiation effects is entering the deep levels of
radiation defects. The concentration of major carriers
reduces, and barrier capacitance dose dependent of the
integrated irradiation flow C (Φ), when they capture the
charge carriers for abrupt p-n-junction, is well described
by the expression [8]:
20
)(2
)(
ÔK
Ñ
D n
e
UU
qN
SÔC
−
+
εε
= , (2)
where ND is the concentration of initial donors in poorly
doped p-n-junction part, U – reverse voltage, UC –
difference of contact potentials, Kn – relative carriers’
removal rate during irradiation or radiation
damageability ⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
Φ
⋅=
d
dn
n
Kn
0
1 , S – junction area.
This dependence С(Ф) is observed for a certain
range of other irradiation types, including α-particles,
if to take into account the specific radiation
damageability coefficient K. As for low α-particles doses
(Ф ≤ 1012 cm–2), the opposite effect was observed in the
experiment: the irradiated p-n-junction capacitance
measured at T = 300 K is higher than the initial sample
capacitance; while at low temperatures the sample
capacitance drops (Fig. 1). At the same doses, the shift
of direct branches in current-voltage characteristics
toward lower voltages occurs, and appropriative
potential barrier value drops from 6.5 down to 3.5 eV
(Fig. 2).
Fig. 1. Capacitance-voltage characteristics of initial and α-
irradiated GaP:N LEDs measured at 300 and 77 K: 1, 3 –
initial samples; 2, 4 – irradiated with Ф = 1012 α-particles/cm2.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 2. P. 183-187.
doi: 10.15407/spqeo19.02.183
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
185
Fig. 2. Current-voltage characteristics of initial (1, 2) and α-
irradiated (3, 4) with Ф = 1012 cm–2, Е = 26 МеV GaP:Zn,O
LEDs measured at 300 and 77 K.
Opposite changes in the irradiated p-n-junction
capacitance measured at 77 and 300 K indicate the
dependence of the defects charge state introduced by α-
particles relatively to the Fermi level EF position in
semiconductor. It is possible to obtain temperature
dependence of EF, being based on the known ionization
energy values of major donors and acceptors (Te and
Zn) in GaP.
The carrier charge concentration dependences on
temperature for n- and p-types of materials are given in
Fig. 3. In the former case, the conductivity is determined
by one level (Ed = 0.14 eV), and in the latter one by two
nearly lying activation energies (Ea1 = 0.071 еV, Ea2 =
0.04 еV). The difference in the donor ionization energy
values Ed = 0.14 eV and Ed
Te = 0.09 eV is apparently
caused by a high compensation level of the studied
crystal conductivity [9].
Fig. 3. Dependences of the charge carrier concentration on
temperature for: 1 – n-type conductivity (Ed = 0.14 eV) and 2 –
p-type conductivity (Ea1 = 0.071 eV and Ea2 = 0.04 eV) GaP
crystals.
The average acceptor activation value energy is
close to Ea
Zn = 0.06 eV. To assess the relationship
between the position of EF on temperature, we used
activation energies values Ed
Te = 0.09 eV and Ea
Zn =
0.06 eV, being based on the calculation methods
proposed in [10].
At low temperatures, when ionized donor impurity
dominated in changing the carrier concentration
(p << ND
+), the neutrality equation simplifies and takes
the form [10]:
12
F
F
+
=== −
−
−
kT
EE
D
D
kT
EE
C d
C
e
NpeNn , (3)
where pD is the hole concentration on donors.
By denoting χ=kT
E
e
F
, we get a quadratic equation,
solution of which is as follows:
⎟
⎟
⎟
⎠
⎞
⎜
⎜
⎜
⎝
⎛
−⋅+=χ
Δ
181
4
1 kT
E
C
DkT
E DD
e
N
Ne . (4)
Then
⎟
⎟
⎟
⎠
⎞
⎜
⎜
⎜
⎝
⎛
−⋅+=
Δ
181
4
1lnF
kT
E
C
DkT
E DD
e
N
NekTE , (5)
where ∆ED is the energy of impurity ionization.
At low temperatures:
18
>>⋅=
Δ
kT
E
C
D
D
e
N
NA , (6)
C
DDC
N
NkTEEE
2
ln
22F +
+
= . (7)
Let us estimate the value A in GaP for two
temperatures: 77 and 300 K. Considering
32377
GaP, m1075.6 −⋅=CN , 324300K
,GaP m102.5 −⋅=CN , ∆ED =
0.09 eV, obtain 99079577K
GaP =A , 5300K
GaP ≅A . So, to
obtain EF (T) dependence at temperatures close to the
room one, it is necessary to use the exact ratio (5), at low
temperatures – expression (7).
The calculation results of EF (T) for n-type gallium
phosphide are shown in Fig. 4. We see that at T = 77 K
the Fermi level is situated 0.05 eV below the conduction
band bottom; temperature increase shifts the EF position
towards the forbidden gap middle, and at T = 300 K EF is
at the distance greater than 0.1 eV from the bottom of
the conduction band EC. The donor level of ~0.1 eV
depth at T = 77 K is fully filled in and can not affect the
barrier capacitance value. When approaching to room
temperature, recharging the level occurs. It ionizes and
begins to affect the junction capacitance by increasing it.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 2. P. 183-187.
doi: 10.15407/spqeo19.02.183
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
186
Fig. 4. Dependence of the Fermi level position on temperature
in n-type GaP, n = 1017 cm–3.
Sulfur impurity with the ionization energy Ed =
0.104 eV [9] as uncontrolled and introduced during
irradiation might be such center. Indeed, bombardment
of the crystal GaP with α-particles (E = 27.2 MeV)
causes reactions in the P15
31 and Ga31
69 nuclei, as the α-
particle energy is much higher than penetration threshold
for both mentioned nuclei P
bE = 9.55 MeV –
phosphorous and Ga
bE = 13.33 MeV – gallium.
0
17
34
15
31 ClP n+→α+ ++ , (8)
stable
16
34
β
32.2min
17
34 SCl
+
→ , (9)
γAsαGa 33
73
31
69 +→+ ++ , =2
1
T 90 days, (10)
stable
33
75
31
71 AsαGa →+ ++ . (11)
Prevalence of P15
31 isotope is 100%, Ga31
69 ,
Ga31
71 isotopes are 60.4 and 39.6%, respectively [11, 12].
As it is obvious from the daughter products scheme, in
all three cases gallium phosphide is doped by donors,
including sulfur. This is fully consistent with previously
made assumptions about the donor’s role with the 0.1 eV
depth in the increasing capacitance process of irradiated
p-n-junction at T = 300 K. In the junction p-region, this
effect should be opposite, but it is nearly invisible
because of a much higher doping level, and thus its
influence on the p-n-transition capacitance is much
weaker.
To ensure the correctness of such considerations,
let us estimate the quantitative contribution of the
inelastic collisions of α-particles with Ga and P nuclei. It
is small. The cross sections of these processes are
determined by a nuclear interaction radius, which is
about one Fermi (10–13 cm) and for an intermediate α-
particle energy (including Eα = 27.2 MeV) are equal to
1…100 mbarn. Since α-particle interaction with nucleus
is single-stage, no need to consider repeated interaction
acts and cascading function value, one can use the
expression for the number of primary inelastic collisions
α → P as:
Φ⋅σ⋅= aS NN , (12)
where Na is the concentration of phosphorous atoms, σ –
α-particles interaction cross section with Р atoms.
The estimated value of sulfur atoms’ number
NS ≈ 109 is low as compared with the concentration of
atoms in the GaP crystal. By analyzing the irradiation
effects on the investigated structure, we must also take
into account the interaction specificity of the heavy
doubly charged particle with crystal atoms. Comparison
of line energy loss for a heavy charged particle on atom
displacement and ionization gives:
310≅
⎟
⎠
⎞
⎜
⎝
⎛
⎟
⎠
⎞
⎜
⎝
⎛
dis
ion
dx
dE
dx
dE
. (13)
So, most of the α-particles energy is spent on
ionization.
It was shown [6] that in polar semiconductors, as
well as in irradiated with low doses GaP, the role of
getering the radiation-stimulated defects is increased,
which results in increasing the minority carriers’
lifetime, diffusion length and others. This effect is
strengthen by recombination-accelerated diffusion
mechanisms that can effectively manifest itself in wide-
gap semiconductors [12].
Therefore, in the wide-zone GaP at high ionization
levels simultaneously with S donor’s concentration
increasing due to nuclear reactions, the process of
getering can occur – the p-n-transition clearing out of
impurities in metastable state and active replacing
process by the Watkins model [13].
It is clear that the capacitance changes in the red
and green LEDs observed at low α-particle doses occur
due to all the mentioned factors, and sulfur atoms
transition to electrically active donor state dominates, if
the ionization level is sufficiently high.
4. Conclusion
It is shown that the low dose effect appearing in GaP
LEDs irradiated with α-particles (Ф = 2·1012 cm–2),
which manifests itself as “improvement” of parameters:
the junction capacitance increasing at room temperature,
decreasing in the potential barrier between p-n-regions
and the differential resistance value in CVC. These
features are caused by α-particle nuclear reactions and
high ionization levels that give rise to additional donors.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 2. P. 183-187.
doi: 10.15407/spqeo19.02.183
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
187
The nuclear reactions product: donors S and interstitial
atoms S, which can substitute phosphorous atoms at high
ionization level and are responsible for the effect. At
high excitation of the crystal electron subsystem
significant contribution to the structural ordering of the
transition region provides the effect of radiation-
stimulated defects’ getering.
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