Thermally stimulated conductivity in InGaAs/GaAs quantum wire heterostructures
Thermally stimulated conductivity of the InGaAs-GaAs heterostructures with quantum wires was studied using different quantum energies of exciting illumination. The structures reveal long-term photoconductivity decay within the temperature range 100 to 200 K, and effect of residual conductivity after...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2016
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| Цитувати: | Thermally stimulated conductivity in InGaAs/GaAs quantum wire heterostructures / S.A. Iliash, S.V. Kondratenko, A.S. Yakovliev, Vas.P. Kunets, Yu.I. Mazur, G.J. Salamo // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2016. — Т. 19, № 1. — С. 75-78. — Бібліогр.: 7 назв. — англ. |
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irk-123456789-1215282017-06-15T03:05:42Z Thermally stimulated conductivity in InGaAs/GaAs quantum wire heterostructures Iliash, S.A. Kondratenko, S.V. Yakovliev, A.S. Kunets, Vas.P. Mazur, Yu.I. Salamo, G.J. Thermally stimulated conductivity of the InGaAs-GaAs heterostructures with quantum wires was studied using different quantum energies of exciting illumination. The structures reveal long-term photoconductivity decay within the temperature range 100 to 200 K, and effect of residual conductivity after turning-off the illumination. Analyzing the data of thermally stimulated conductivity, the following energies of electron traps were found: 90, 140, and 317 meV. The role of deep traps in recombination process as well as the photoconductivity mechanism was discussed. 2016 Article Thermally stimulated conductivity in InGaAs/GaAs quantum wire heterostructures / S.A. Iliash, S.V. Kondratenko, A.S. Yakovliev, Vas.P. Kunets, Yu.I. Mazur, G.J. Salamo // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2016. — Т. 19, № 1. — С. 75-78. — Бібліогр.: 7 назв. — англ. 1560-8034 DOI: 10.15407/spqeo19.01.075 PACS 72.40.+w, 73.40.-e, 73.63.Nm http://dspace.nbuv.gov.ua/handle/123456789/121528 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Thermally stimulated conductivity of the InGaAs-GaAs heterostructures with quantum wires was studied using different quantum energies of exciting illumination. The structures reveal long-term photoconductivity decay within the temperature range 100 to 200 K, and effect of residual conductivity after turning-off the illumination. Analyzing the data of thermally stimulated conductivity, the following energies of electron traps were found: 90, 140, and 317 meV. The role of deep traps in recombination process as well as the photoconductivity mechanism was discussed. |
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Article |
| author |
Iliash, S.A. Kondratenko, S.V. Yakovliev, A.S. Kunets, Vas.P. Mazur, Yu.I. Salamo, G.J. |
| spellingShingle |
Iliash, S.A. Kondratenko, S.V. Yakovliev, A.S. Kunets, Vas.P. Mazur, Yu.I. Salamo, G.J. Thermally stimulated conductivity in InGaAs/GaAs quantum wire heterostructures Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Iliash, S.A. Kondratenko, S.V. Yakovliev, A.S. Kunets, Vas.P. Mazur, Yu.I. Salamo, G.J. |
| author_sort |
Iliash, S.A. |
| title |
Thermally stimulated conductivity in InGaAs/GaAs quantum wire heterostructures |
| title_short |
Thermally stimulated conductivity in InGaAs/GaAs quantum wire heterostructures |
| title_full |
Thermally stimulated conductivity in InGaAs/GaAs quantum wire heterostructures |
| title_fullStr |
Thermally stimulated conductivity in InGaAs/GaAs quantum wire heterostructures |
| title_full_unstemmed |
Thermally stimulated conductivity in InGaAs/GaAs quantum wire heterostructures |
| title_sort |
thermally stimulated conductivity in ingaas/gaas quantum wire heterostructures |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2016 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/121528 |
| citation_txt |
Thermally stimulated conductivity in InGaAs/GaAs quantum wire heterostructures / S.A. Iliash, S.V. Kondratenko, A.S. Yakovliev, Vas.P. Kunets, Yu.I. Mazur, G.J. Salamo // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2016. — Т. 19, № 1. — С. 75-78. — Бібліогр.: 7 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
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AT iliashsa thermallystimulatedconductivityiningaasgaasquantumwireheterostructures AT kondratenkosv thermallystimulatedconductivityiningaasgaasquantumwireheterostructures AT yakovlievas thermallystimulatedconductivityiningaasgaasquantumwireheterostructures AT kunetsvasp thermallystimulatedconductivityiningaasgaasquantumwireheterostructures AT mazuryui thermallystimulatedconductivityiningaasgaasquantumwireheterostructures AT salamogj thermallystimulatedconductivityiningaasgaasquantumwireheterostructures |
| first_indexed |
2025-07-08T20:02:57Z |
| last_indexed |
2025-07-08T20:02:57Z |
| _version_ |
1837110372298915840 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 1. P. 75-78.
doi: 10.15407/spqeo19.01.075
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
75
PACS 72.40.+w, 73.40.-e, 73.63.Nm
Thermally stimulated conductivity
in InGaAs/GaAs quantum wire heterostructures
S.A. Iliash1, S.V. Kondratenko1, A.S. Yakovliev1, Vas.P. Kunets2, Yu.I. Mazur2, and G.J. Salamo2
1Taras Shevchenko National University of Kyiv,
64/13, Volodymyrs’ka str., 01601 Kyiv, Ukraine
E-mail: iliashsviatoslav@gmail.com
2Institute for Nanoscience and Engineering, University of Arkansas,
Fayetteville, AR 72701, USA
Abstract. Thermally stimulated conductivity of the InGaAs-GaAs heterostructures with
quantum wires was studied using different quantum energies of exciting illumination.
The structures reveal long-term photoconductivity decay within the temperature range
100 to 200 K, and effect of residual conductivity after turning-off the illumination.
Analyzing the data of thermally stimulated conductivity, the following energies of
electron traps were found: 90, 140, and 317 meV. The role of deep traps in recombi-
nation process as well as the photoconductivity mechanism was discussed.
Keywords: heterostructure, quantum wire, photoconductivity.
Manuscript received 24.11.15; revised version received 03.02.16; accepted for
publication 16.03.16; published online 08.04.16.
1. Introduction
Nowadays the interest in studying the physical
properties of heterostructures InGaAs-GaAs, specifically
centers with deep and shallow trap levels, has increased
significantly [4-7]. It is caused by its successful use to
solve the scientific and technical problems for several
years. InGaAs-GaAs heterostructure with quantum wires
(QWR) are known for their unique photoelectrical
properties that are perspective for implementation of
new phototransistor technologies, infrared photo-
detectors and solar cells.
Like to other semiconductor materials, deep defect
states in the band gap of InGaAs are formed by doping
with a wide class of impurities [5]. These states may be
significantly complicated due to formation of dopant
pairs or their interaction with their own lattice defects.
Optical and electronic properties are studied by
photocurrent (PC) spectra and thermal activation effects
measurement [3]. However, thermally stimulated
conductivity (TSC) spectra of InGaAs-GaAs hetero-
structures with QWR are not examined enough.
According to [1-3], distribution of localized states in
semiconductors is based on the multiple trapping model.
It was shown that peaks in the spectra TSC were
observed within the temperature range 100…150 K.
The main goal of this work is to obtain TSC spectra
for heterostructures InGaAs-GaAs and to interprete
them. To reach the goal, the classic method for obtaining
TSС spectra and periodic light excitation method during
the heating from 83 to 276 K were used in this paper.
2. Experimental details
All heterostructures were grown on GaAs (311)A semi-
insulating substrates by using molecular beam epitaxy.
After growing the 0.5-μm GaAs buffer layer at 580 °С,
the substrate temperature was reduced down to 520 ºС
for deposition of the InGaAs and n-type GaAs barriers.
Five periods of InGaAs/GaAs were deposited with 6, 8,
10 and 11 monolayers (MLs) of In0.38Ga0.62As. Each
GaAs barrier was 40-nm thick consisting of 10-nm
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 1. P. 75-78.
doi: 10.15407/spqeo19.01.075
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
76
undoped GaAs, then 20-nm uniformly doped GaAs:Si
(Nd = 5·1017 cm–3), and then another 10-nm undoped
GaAs. Finally, each sample was capped with a final
InGaAs QWR layer of equal deposition to the buried
QWRs for AFM study. Samples with 11 and 10 MLs of
InGaAs deposition are shown to form high-quality
QWRs [7], while structures with 6 and 8 MLs maintain
quantum well-like nature.
In order to get results, firstly, we cooled the
sample to the temperature of 83 K, then linearly heated
and periodically lighted samples (for 30 s). Spectra of
lateral PC for 11 ML InGaAs-GaAs QWR hetero-
structure measured within the range 0.6…2.0 eV at the
temperature 83 K. The time dependence of PC rise and
decay obtained during excitation by using light with
energies hν1 = 1.35 eV and hν2 = 1.65 eV within the
temperature range 83 to 296 K.
3. Results and discussion
Fig. 1 shows the time dependence of photoconductivity
damping and decay, measured at different temperatures
for InGaAs-GaAs structure with light excitation hν1 =
1.35 eV and hν2 = 1.65 eV. This experiment was
performed under the condition of a linear temperature
increase at the speed close to 0.05 K/s, and therefore, a
change in temperature during the relaxation process is
negligible (see Fig. 2a, insert). The kinetics of PC decay
was described by a stretched exponential dependence:
PCI ∼ ( ){ }β
τ− texp , (1)
where τ is the time constant, β – ideality factor, which is
equal to β = 0.7 for the studied structures. Note that the
law proved to an exponential PC increase, and the ratio
of time decay constant to the time increase one was
52.2=τ
τ
rise
dec . It means that in addition to
recombination centers, long term electronic traps
(shallow trap centers) have a significant impact on PC
decay [4, 6].
Fig. 1. Growth diagram of InGaAs-GaAs heterostructure.
Fig. 2a shows the extended relaxation (residual
photoconductivity), when conductivity is not returned to
its equilibrium value for a long (~30 s) time, under
excitation hν1 = 1.35 eV at temperatures between 120
and 150 K. We can distinguish two peaks of thermal
conductivity in the dark background of conductivity
(dashed curve), which is measured under similar
experimental conditions, but without photoexcitation.
Energy hν1 and hν2 were selected being based on the
analysis of the spectral dependence of InGaAs-GaAs
structure (Fig. 3), measured at 83 K. Photocurrent
spectroscopy reveals several electron transitions
indicating the complicated density of states spectrum in
our samples (Fig. 3). Besides electron transitions
between ground states of conduction and valence bands
of InGaAs QWR (arrow 1), the PC signal below band
gap of GaAs is the result of photoexcited electrons in
both the buffer layer (arrow 2) and defect states of GaAs
(arrows 4 and 5) [4]. Band-to-band absorption in GaAs
is observed above 1.43 eV (arrow 3). The energy hν1 =
1.35 eV causes resonant excitation of InGaAs QWR as a
result of band-to-band transitions, while hν2 = 1.65 eV is
also responsible for possible excitation of electron-hole
pairs in GaAs. In addition, PC within the spectral range
0.7…1.3 eV is caused by transitions between GaAs deep
states. These energies determined in [6] indicate the
presence of deep levels in the system.
Fig. 4 shows the TSC curve for InGaAs-GaAs
11 ML structure, measured by heating after excitation
hν1 = 1.35 eV. We can select a wide peak of thermal
conductivity, but in contrast to the kinetic method, we
cannot distinguish the detail structure of the TSC
spectrum.
9
10
11
12
0 5 10 15 20 25 30 35
9.3
9.4
9.5
9.6
9.7
9.8
9.9
10
0 500 1000 1500 2000 2500 3000 3500
8
9
10
11
12
0 5 10 15 20 25 30 35
9.3
9.4
9.5
9.6
9.7
9.8
9.9
10
10.1
10.2
a)Ph
ot
oc
ur
re
nt
, μ
A
PC(hν1)
Currentdark
Ph
ot
oc
ur
re
nt
, μ
A
Time, s
Ph
ot
oc
ur
re
nt
, μ
A
Time, s
PC(hν2)
Currentdark
b)
Ph
ot
oc
ur
re
nt
, μ
A
Time, s
85K 300KTemperature, K
Fig. 2. Time dependences of PC relaxation under light excita-
tion hν1 (a) and hν2 (b) and various temperatures (83…276 K).
(The dashed line corresponds to the dark current.)
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 1. P. 75-78.
doi: 10.15407/spqeo19.01.075
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
77
80 100 120 140 160 180 200 220 240 260
8.0
8.5
9.0
9.5
10.0
10.5
11.0
11.5
12.0
80 100 120 140 160 180
0.0
0.1
0.2
0.3
0.4
80 100 120 140 160 180 200 220
0.0
0.1
0.2
0.3
0.4
Ph
ot
oc
ur
re
nt
, μ
A
Temperature, K
Dark
All
Light
a)
Ph
ot
oc
ur
re
nt
, μ
A
Temperature, K
b)
Ph
ot
oc
ur
re
nt
, μ
A c)
Fig. 5. (а) Dependence of the TSC spectra on heating (excitation hν1 = 1.35 eV). Thermally stimulated conductivity of the sample
11 ML InGaAs-GaAs for various excitation intensities, (b) for hν1 = 1.35 eV, (с) for hν2 = 1.65 eV.
0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
11.5
11.6
11.7
11.8
11.9
12.0
12.1
12.2
12.3
Ph
ot
oc
ur
re
nt
, μ
A
hν, eV
Fig. 3. Spectra of lateral PC for 11 ML InGaAs-GaAs QWR
heterostructure measured at 83 K. The bias voltage 100 mV
was applied along QWR ( [ ]332 direction).
TSC peak with a maximum at 160 K was observed
within the temperature range from 130 up to 200 K
(Fig. 4). Assuming that the recapture (capture other
sticking centers) does not happen, we can estimate the
depth of attachment center relative to the conduction
band [5]:
maxB23 Tka =ε , (2)
where kB is the Boltzmann constant, Tmax – temperature
of the TSC peak. This formula is simplified and provides
a relatively large error in assessing the activation energy.
Using the equation (2), we can give rough estimate of
the localization depth of charge carrier on a shallow
center relatively to the center of the conduction band εa =
317 meV.
100 150 200 250 300
8.0
8.5
9.0
9.5
10.0
10.5
Ph
ot
oc
ur
re
nt
, μ
A
Time, s
Temperature
TSC
Fig. 4. Classical thermally stimulated conductivity for InGaAs-
GaAs 11 ML heterostructure.
Considering the shallow centers that are surrounded
by QWR, it is possible that they determine the hetero-
structure conductivity in non-equal state. Due to the fact
that the studied heterostructure has trapping center for
electrons, it can be argued that the excited QWR have
negatively charged environment.
Temperature dependence of PC decay shown in
Figs. 5a, 5b for hν1 = 1.35 eV and 5c for hν2 = 1.65 eV.
We can see that in both cases two TSC peaks, but for hν1
(Fig. 4c) the spectrum is more extended and shifted into
the region of higher temperatures.
Fig. 5 shows that the activation energy for electrons
at excitation hν1 (1.35 eV) is equal to εa = 229 meV for
the first maximum and to εa = 337 meV for the second
one. The activation energy at excitation hν2 (1.65 eV) is
equal to εa = 218 meV for the first maximum and to
εa = 278 meV for the second maximum.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 1. P. 75-78.
doi: 10.15407/spqeo19.01.075
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
78
W
=
1
01
m
ev
540 550 560 570 580 590 600 610 620 630 640
-0.05
0.00
0.05
0.10
0.15
0.20
εQWR
a = 142meV
En
er
gy
, e
V
Position, nm
εAsGa
a = 87meV
Fig. 6. Energy band diagram of the 11 ML InxGa1–xAs
structure. Where x = 0.38, QWR height is 3.8 nm.
When we use the formula (2) for assessing the
activation energy, we obtain a sufficiently large error,
because the formula is simplified and ignores the
multiple trapping. The resulting activation energy was
much higher than the values obtained from the analysis
of TSС kinetic method. It means that at stationary filling
TSС revealed deep electronic states.
Fig. 6 shows a diagram of the energy levels in the
11 ML InxGa1–xAs heterostructure, calculated using the
software NextNano3 with the parameters x = 0.38 and
QWR height of 3.8 nm. We revealed that the structure is
characterized by potential variation caused by the inter-
mediate layers of doped GaAs, which creates potential
parabolic quantum wells (W = 101 meV). In addition,
the system has quantum-sized states implied by the mo-
vement restriction of charge carriers in InxGa1–xAs
QWR. Thus, the system includes two subsystems of
quantum-sized states due to the electron movement
restriction in either GaAs buffer layer, or in InxGa1–xAs
QWR. According to band diagram calculations of the
activation energy for GaAs and QWR, potential wells
were equal to εa = 87 meV and εa = 142 meV,
respectively. Electrons are localized at a minimum of
GaAs and can be spatially separated from the holes.
These photoelectrons cause extended photocurrent
relaxation, because for their recombination with holes in
InxGa1–xAs it is necessary to overcome the potential
barrier height GaAs
aε = 87 meV (see Fig. 6).
It was found that the temperature dependence of the
time constant τ within the temperature range between 80
and 150 K agrees well with Arrhenius behavior of decay,
when ( )Tτln ~ kTaε . After analyzing the dependence
of τ on temperature for hν1 = 1.35 eV and hν2 = 1.65 eV,
we obtained the activation energies εa = 146 meV and
εa = 92 meV, respectively. With account of the
importance of energy activation for potential wells in
GaAs and QWR, obtained from the band energy
diagram, we conclude that electrons mainly fill the
quantum states of QWR under excitation hν1, and
electrons fill GaAs potential well under excitation hν2.
Consequently, we get the photocurrent relaxation
processes involving different energy states
(recombination centers) when light excitation with
different energies (1.35, 1.65 eV) is used.
4. Conclusions
Thermally stimulated conductivity of the InGaAs-GaAs
heterostructures with quantum wires was studied using
different quantum energies of exciting illumination. The
spectrum of electronic states that determines recom-
bination in InGaAs-GaAs heterostructures was obtained
at different temperatures, using the TSС method and
kinetic one with periodic illumination of the sample. The
structures reveal long-term photoconductivity decay
within the temperature range 100…200 K and effect of
residual conductivity after turning-off the illumination.
Analyzing the data of thermally stimulated conductivity,
the following energies of electron traps were found: 90,
140, and 317 meV. The obtained activation energy for
potential wells of the band structure and studied
temperature dependence of the time constant τ show that
light excitation with a selective energy for InxGa1–xAs
QWR leads to increase in PC caused by electrons
concentrated in QWR.
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4. S.V. Kondratenko, O.V. Vakulenko, Vas.P. Kunets,
Y.I. Mazur, V.G. Dorogan, M.E. Ware & G.J.
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