Features of current-voltage characteristics inherent to GaP light-emitting diodes with quantum wells
In this work, GaP p-n junctions used in light-diode manufacturing were studied using the electrophysical methods at various temperatures. Current-voltage characteristics of some diodes, controlled by PC and measured in the voltage and current generator modes with various steps, have shown irregulari...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2006
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| Цитувати: | Features of current-voltage characteristics inherent to GaP light-emitting diodes with quantum wells / O. Konoreva, V. Opilat, M. Pinkovska, V. Tartachnyk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 4. — С. 45-48. — Бібліогр.: 14 назв. — англ. |
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irk-123456789-1216332017-06-16T03:03:14Z Features of current-voltage characteristics inherent to GaP light-emitting diodes with quantum wells Konoreva, O. Opilat, V. Pinkovska, M. Tartachnyk, V. In this work, GaP p-n junctions used in light-diode manufacturing were studied using the electrophysical methods at various temperatures. Current-voltage characteristics of some diodes, controlled by PC and measured in the voltage and current generator modes with various steps, have shown irregularities in the regions of negative differential resistance and specific before-breakdown part. Long-lasting relaxation of conductivity of GaP crystal with nonuniformity of defect distribution was observed. From analysis of current-flow mechanisms, it was proposed that atypical GaP light-diode electrical characteristics degradation is caused by complex traps shaped as quantum wells in the p-n junction. 2006 Article Features of current-voltage characteristics inherent to GaP light-emitting diodes with quantum wells / O. Konoreva, V. Opilat, M. Pinkovska, V. Tartachnyk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 4. — С. 45-48. — Бібліогр.: 14 назв. — англ. 1560-8034 PACS 68.35, 73.40. K http://dspace.nbuv.gov.ua/handle/123456789/121633 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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In this work, GaP p-n junctions used in light-diode manufacturing were studied using the electrophysical methods at various temperatures. Current-voltage characteristics of some diodes, controlled by PC and measured in the voltage and current generator modes with various steps, have shown irregularities in the regions of negative differential resistance and specific before-breakdown part. Long-lasting relaxation of conductivity of GaP crystal with nonuniformity of defect distribution was observed. From analysis of current-flow mechanisms, it was proposed that atypical GaP light-diode electrical characteristics degradation is caused by complex traps shaped as quantum wells in the p-n junction. |
| format |
Article |
| author |
Konoreva, O. Opilat, V. Pinkovska, M. Tartachnyk, V. |
| spellingShingle |
Konoreva, O. Opilat, V. Pinkovska, M. Tartachnyk, V. Features of current-voltage characteristics inherent to GaP light-emitting diodes with quantum wells Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Konoreva, O. Opilat, V. Pinkovska, M. Tartachnyk, V. |
| author_sort |
Konoreva, O. |
| title |
Features of current-voltage characteristics inherent to GaP light-emitting diodes with quantum wells |
| title_short |
Features of current-voltage characteristics inherent to GaP light-emitting diodes with quantum wells |
| title_full |
Features of current-voltage characteristics inherent to GaP light-emitting diodes with quantum wells |
| title_fullStr |
Features of current-voltage characteristics inherent to GaP light-emitting diodes with quantum wells |
| title_full_unstemmed |
Features of current-voltage characteristics inherent to GaP light-emitting diodes with quantum wells |
| title_sort |
features of current-voltage characteristics inherent to gap light-emitting diodes with quantum wells |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2006 |
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http://dspace.nbuv.gov.ua/handle/123456789/121633 |
| citation_txt |
Features of current-voltage characteristics inherent to GaP light-emitting diodes with quantum wells / O. Konoreva, V. Opilat, M. Pinkovska, V. Tartachnyk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 4. — С. 45-48. — Бібліогр.: 14 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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2025-07-08T20:15:16Z |
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| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 4. P. 45-48.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
45
PACS 68.35, 73.40. K
Features of current-voltage characteristics inherent
to GaP light-emitting diodes with quantum wells
O. Konoreva1, V. Opilat2, M. Pinkovska1, V. Tartachnyk1
1Institute for Nuclear Research, NAS of Ukraine, 47, prospect Nauky, 03028 Kyiv, Ukraine
2Drahomanov National Pedagogical University, 9, Pirohova str., 01601 Kyiv, Ukraine
Corresponding author: phone: +044-525-37-49, fax: +044-525-44-63
E-mail: myrglory@yahoo.com; opylat@ua.fm
Abstract. In this work, GaP p-n junctions used in light-diode manufacturing were
studied using the electrophysical methods at various temperatures. Current-voltage
characteristics of some diodes, controlled by PC and measured in the voltage and current
generator modes with various steps, have shown irregularities in the regions of negative
differential resistance and specific before-breakdown part. Long-lasting relaxation of
conductivity of GaP crystal with nonuniformity of defect distribution was observed.
From analysis of current-flow mechanisms, it was proposed that atypical GaP light-diode
electrical characteristics degradation is caused by complex traps shaped as quantum wells
in the p-n junction.
Keywords: GaP, current-voltage characteristics, irregularities, complex traps, quantum
wells, conductivity relaxation.
Manuscript received 23.05.06; accepted for publication 23.10.06.
1. Introduction
Stability of element base parameters of modern solid-
state radioelectronic devices is mainly determined by the
quality of their active regions: p-n junctions, hetero-
structures, and metal-semiconductor junctions. And the
perfection of semiconductor interface layers used in a
micromodule device fabrication is a problem, especially,
for such material as GaP. For example, nearly thirty
years ago it was discovered using the positron
annihilation method that the GaP film-substrate interface
was enriched by vacancies, and 200 ºC annealing tended
to polivacancy cluster creation [1]. The high density of
dislocations that can grow at the whole upper layer depth
and thus influence on the device characteristics was
obtained in [1-4]. Different aspects of defect structure of
GaP exposed to ionizing radiation, are studied till now
(see for example [5-7]). But knowledge of the defectness
of p-n junction as a prerequisite of light-diode operating
characteristics is still desirable.
In this article, the defect states of CZ GaP p-n
junctions used in light-diode fabrication were studied
using the electrophysical methods (conductivity,
capacity-voltage and current-voltage dependences). This
makes it possible to study mechanisms and processes
that occur in the p-n junction. The main attention was
paid to the appearance of irregularities in current-voltage
characteristics, especially the regions with negative
differential resistance and breakdown. In some devices
the observed anomalies of electrical characteristics and
long-lasting conductivity relaxation are connected with
uniform distribution of impurities and existence of
complex traps shaped as quantum wells in the depletion
region of p-n junction.
2. Experiment
Fabricated GaP light diodes made by the double liquid-
epitaxy method were used. p-n structures with red
emission were doped by Zn and O atoms, and with green
– by N atoms. Conductivity of cross-like GaP samples
was measured as a time function at the room temperature
after thermal excitation. The p-n junction parameters were
obtained from capacity-voltage measurements. Current-
voltage characteristics (CurVC) of light diodes controlled
by PC in the voltage and current generator modes were
studied at the nitrogen and room temperatures. The
opportunity to change current or voltage steps makes it
possible nearly to instantly make measurements and thus
to observe a thin structure in CurVC of GaP p-n junction.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 4. P. 45-48.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
46
50
40
30
20
10
0
0 5 10 15 20
U, V
I,
m
A
300K
77K
Fig. 2. Current-voltage characteristics of GaP light-emitting
diode measured at various temperatures.
3. Results and discussion
Changes of conductivity in GaP samples last after
thermal excitation for several dozen of minutes at room
temperature (Fig. 1). As shown in [8-10], relaxation
curves σ(t) are formed in crystals that possess non-
uniform impurity distribution. In order to explain the
relaxation mechanism, the band scheme that included
defect clusters (shown in the insert in Fig. 1) was used. It
makes it possible to estimate the main cluster
parameters, namely: the potential barrier height and
geometric dimensions.
Equations that describe the barrier height φeff and
effective cluster radius Reff are [8]:
ff
eff
eR
e
ε
ϕ h
= , (1)
22*
22
eff 8 Tkm
eR
ε
ηh
= , (2)
where η is the defect concentration in a cluster, e, ћ, ε, T,
k are the well-known physical parameters.
Using the well-known relations for the time-
dependent conductivity
⎟
⎠
⎞
⎜
⎝
⎛−+= ∞ τ
σσσ tt exp)( 0 (3)
and lifetime
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
=
kT
eeff
0 exp
ϕ
ττ (4)
from the experimental data, one can estimate the defect
concentration in a cluster, its effective radius and
potential barrier around it.
Fig. 1. Time-dependent conductivity relaxation of GaP crystal
at the room temperature. Band scheme that includes defect
clusters is shown in the insert.
As relaxation processes proceed long enough (some
dozens of minutes), the calculated from Eq. (1) potential
barrier is essential, it equals nearly 0.7-0.9 eV. The
effective cluster radius of about 40-60 Å (Eq. (2))
responds to it.
Forward CurVC of some red and green GaP light-
diodes, made of such crystal and used in investigations,
possess anomalies. I-U curves of diodes measured with
low current steps display separate oscillations at 70-90 K
(Fig. 2) and a characteristic negative differential
resistance region (NDR) is observed just before this re-
gion. The origin and main details concerning the current
flow in NDR were studied previously in detail [11].
At reverse bias, the situation is quite different.
Some light diodes measured at the room temperature for
4 times, display atypical reverse I-U dependences too,
and the current curve shape depends upon the number of
the measurement (Fig. 3). One can see that the measured
for the first time reverse I-U dependence is characterized
by the minimum (curve 1), and its deepness decreases
with repeating the measurements. At last after 4 cycles,
the current curve shape has become similar to that
obtained at 77 K. It was stated experimentally that to
reach again a reproduction of the reverse I-U curve with
the minimum (after 4 measurements and obtaining the
smooth curve), it was necessary to keep the sample at
the nitrogen temperature for 10 min. The nature of
current recovering needs an additional investigation.
It is worthy to mention once more that, as a rule,
the experimental curves correspond to ideal p-n junction
characteristics, and only in some investigations the
current curve possesses minimum.
In a contrast with the previous case (300 K), the
reverse I-U dependence at 77 K is typical for p-n
junction and is caused by minority carrier flow that is
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 4. P. 45-48.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
47
followed by the breakdown region. This curve nearly
coincides with the room temperature reverse
characteristics, obtained for the last measurement of
cycle (see curve 4 in Fig. 3). The first part of the curve is
practically temperature independent till starting the
breakdown.
Let us analyze a possible mechanism of the atypical
I-U dependences. Thermal p-n junction breakdown is
caused by the conductivity increase with temperature.
So, it is difficult to explain the negative resistance region
with minimum changing during every cycle. The
avalanche breakdown is characterized by a sharp (near-
vertical) current dependence on the voltage. So, one can
suppose large-dimension structure defects that provoked
long-lasting relaxation processes influence on the
atypical reverse current. As shown previously by
studying conductivity relaxation in GaP, clusters with
radius close to several dozens of angstroms can exist in
crystal used for light-emitting diode manufacturing. If
such defects are shaped as the wells, surrounded by
barriers, as shown in the insert in Fig. 1, the wells can
store the current carriers and then return them (under
specific conditions) to the conduction or valence bands.
In the case, the defects are in the depleted diode region,
the p-n junction field changes unequally barrier height
from the both well sides: namely, by increasing a barrier
height from the one side, and decreasing – from another.
Thus, the conditions are created for over-barrier
emission and for the increase of the tunneling probability
(see Fig. 4).
From the CurVC measurements, one can evaluate
the maximum field E in a p-n junction [12]:
( )
( ) C
zS
UUz
E k
1−
+
=
ε
. (5)
0-5-10-15-20-25
-1,0
-2,0Irev, mA
Urev, V
1
2
3
4
Fig. 3. Atypical GaP diode current-voltage characteristics
measured repeatedly (curves 1-4) at 300 K. The latter curve 4
coincides with the characteristics measured at 77 K.
V
C
Fig. 4. Schematic band structure of the initial crystal with
impurities, shaped as “quantum wells”.
It follows from the I-U curve slope z = 2. Uk –
contact potential, U – reverse voltage. The diode
parameters: area S = 1 mm2, barrier capacity C = 60 pf.
Then E =3.6ּ106 V/cm.
When the reverse bias reaches the value, at which
the minimum in the I-U curve occurs (Ur = 10 V),
( )m
V1072.9)V10( 6⋅=E . (6)
Initial field of the cluster surrounded by the barrier,
which was derived from the abovementioned assumption
(concerning the barrier potential φeff = 0.6 eV and radius
r = 60 Å) is close to the same value. So, the tunneling
threshold Ur = 10 V [13] for GaP diode is overcame.
Then, the carrier tunneling through the barrier dominates
in the part where the current increases to the value Imin.
Unfortunately, we can’t confirm the current mechanism
as the tunneling using the slope of current dependence
on temperature, because the value of the current
minimum is changed with repeating the measurements.
Appearance of complex defects shaped as
“quantum wells” may be caused by nonhomogeneities of
the impurity distribution in the initial sample. One can
assume that a local center is situated on the back side of
the central well (shown schematically in Fig. 1). At a
large electrical field, electrons from the filled central part
move through a barrier to the local center with the
following transit to the valence band. The reverse
current increases as the bias increases. If the bias is too
large and the defect level position shifts enough, the
transit of the well-defect has become impossible (dotted
line in Fig. 4). The diode reverse current decreases to the
level of saturation.
An existence of structure defects of quantum well
shape, surrounded by three-dimensional potential
barriers, looks like sample memory, caused by
manufacturing operations. Filling of centers by carriers
may occur due to over-barrier emission at high-
temperature treatment. This state can be storied long
enough, because the barrier height at 300 K is greater
than kT value. Such effect is quite similar to that
observed in the information storage by TLD dosimeter.
Analogous quantum wells are situated randomly in
a crystal. Their influence on reverse currents of p-n
junction is effective only in the case, when some of the
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 4. P. 45-48.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
48
wells appear in the depletion region of the p-n junction.
If the wells are far from the region of the maximum
electrical field, the current-voltage dependences possess
no anomalies.
The decrease of minimum of Ir(Ur) dependence
with every cycle repeating is probably caused by large
junction potential barriers and large relaxation times:
potential wells are not emptied fully in the course of
measurements.
The sharp increase of Ir curve at a high voltage is
caused by the carrier tunneling, as the slope of I-U
curves is the same at 300 and 77 K. Tunneling
breakdown occurs at the voltages e(Ur+Uk) < Eg, when
the band shift allows effective band-to-band tunneling
[14] with the tunnel probability D according to the
equation
⎟
⎟
⎟
⎠
⎞
⎜
⎜
⎜
⎝
⎛
−= ∗
e
g
Wq
E
mD
h
2
3
2
3
4exp , (7)
where We is the current carrier energy, Eg is the
forbidden band width, m*, ћ, q are the crystal
parameters.
3. Conclusion
It has been found the long-lasting relaxation of
conductivity in GaP samples with non-uniformity of the
impurity distribution. Processes are caused by the
existence of complex traps shaped as quantum wells
with several dozens of Angstroem unit dimensions,
which are surrounded by potential barriers with the
barrier height equal to ~0.6 eV.
Current anomalies were observed in some red and
green GaP CurVCs. The region of the sharp reverse
current increase is obvious for the I-U dependences at
300 K, which is followed by negative differential
resistance. The effect is caused by the carrier tunneling
from the quantum well onto the local defect (located in
potential barrier boundaries) and following emission into
the valence band. The quantum wells influence on p-n
junction reverse currents only in the case, when they are
situated in the depletion region of the p-n junction. If
wells are far from the region of the maximum electrical
field, the current-voltage dependences possess no
anomalies.
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