Acoustoelectric transient spectroscopy of microwave treated GaAs-based structures
The effects of microwave (2.45 GHz) treatment influence on the cross section for electron capture and the energy of the deep levels in the forbidden gap of GaAs monocrystals and n-n⁺ epitaxial structures have been investigated using acoustoelectric transient spectroscopy.
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2003
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| Назва видання: | Semiconductor Physics Quantum Electronics & Optoelectronics |
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| Цитувати: | Acoustoelectric transient spectroscopy of microwave treated GaAs-based structures / O.Ya. Olikh // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2003. — Т. 6, № 4. — С. 450-453. — Бібліогр.: 14 назв. — англ. |
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irk-123456789-1180852017-05-29T03:03:06Z Acoustoelectric transient spectroscopy of microwave treated GaAs-based structures Olikh, O.Ya. The effects of microwave (2.45 GHz) treatment influence on the cross section for electron capture and the energy of the deep levels in the forbidden gap of GaAs monocrystals and n-n⁺ epitaxial structures have been investigated using acoustoelectric transient spectroscopy. 2003 Article Acoustoelectric transient spectroscopy of microwave treated GaAs-based structures / O.Ya. Olikh // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2003. — Т. 6, № 4. — С. 450-453. — Бібліогр.: 14 назв. — англ. 1560-8034 PACS: 72.50.+b http://dspace.nbuv.gov.ua/handle/123456789/118085 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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The effects of microwave (2.45 GHz) treatment influence on the cross section for electron capture and the energy of the deep levels in the forbidden gap of GaAs monocrystals and n-n⁺ epitaxial structures have been investigated using acoustoelectric transient spectroscopy. |
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Olikh, O.Ya. |
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Olikh, O.Ya. Acoustoelectric transient spectroscopy of microwave treated GaAs-based structures Semiconductor Physics Quantum Electronics & Optoelectronics |
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Olikh, O.Ya. |
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Olikh, O.Ya. |
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Acoustoelectric transient spectroscopy of microwave treated GaAs-based structures |
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Acoustoelectric transient spectroscopy of microwave treated GaAs-based structures |
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Acoustoelectric transient spectroscopy of microwave treated GaAs-based structures |
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Acoustoelectric transient spectroscopy of microwave treated GaAs-based structures |
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Acoustoelectric transient spectroscopy of microwave treated GaAs-based structures |
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acoustoelectric transient spectroscopy of microwave treated gaas-based structures |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2003 |
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http://dspace.nbuv.gov.ua/handle/123456789/118085 |
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Acoustoelectric transient spectroscopy of microwave treated GaAs-based structures / O.Ya. Olikh // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2003. — Т. 6, № 4. — С. 450-453. — Бібліогр.: 14 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
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AT olikhoya acoustoelectrictransientspectroscopyofmicrowavetreatedgaasbasedstructures |
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2025-07-08T13:20:27Z |
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2025-07-08T13:20:27Z |
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1837085048542593024 |
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Semiconductor Physics, Quantum Electronics & Optoelectronics. 2003. V. 6, N 4. P. 450-453.
© 2003, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine450
PACS: 72.50.+b
Acoustoelectric transient spectroscopy
of microwave treated GaAs-based structures
O.Ya. Olikh
Kyiv Taras Shevchenko National University, Physics Faculty, 6, pr. Glushkova, 03127 Kyiv, Ukraine,
Phone: +380 (44) 2660510, Å-mail: olikh@mail.univ.kiev.ua
Abstract. The effects of microwave (2.45 GHz) treatment influence on the cross section for
electron capture and the energy of the deep levels in the forbidden gap of GaAs monocrystals
and n-n+ epitaxial structures have been investigated using acoustoelectric transient spectroscopy.
Keywords: microwave treatment, deep level, gallium arsenide.
Paper received 30.07.03; accepted for publication 11.12.03.
1. Introduction
The external factors influence on semiconductors and
semiconductor-based structures is widely studied, both
to understand degradation processes into semiconductor
devices and to find new technological decisions of the
such devices fabrication. The influence of some factors,
such as radiation, is studied completely enough [1,2]. In
recent years, a number of papers are devoted to the new
influence methods, such as ultrasonic treatment [3,4] or
microwave (MW) electromagnetic irradiation [5�7]. For
example, it is shown that MW treatment leads to relaxa-
tion of the internal mechanical strain of the Schottky-
barrier GaAs structures [5], redistribution of the impuri-
ties [5,6], gettering of the point defects [7]. However, in-
formation about microwave influence on the structure
defect parameters is practically unknown.
In this paper, we present results of investigation MW
irradiation influence on the parameters of deep levels
located into the under-surface region of n-GaAs mono-
crystals and GaAs n-n+ epitaxial structures.
2. Samples and experimental technique
The following three types of samples were investigated in
this work:
1) The monocrystal GaAs wafer. The (100) wafer,
300 µm thick, was doped with Sn. The electron concen-
tration was (1.5÷2.5)×1018 cm�3 (for the sample labeled
as GA1) or (3÷5)×1016 cm�3 (sample GA2). The (111) wa-
fer, 300 µm thick, doped with Te, n = (1÷2)×1018 cm�3,
labeled GA3;
2) The GaAs epitaxial n-n+ structures. The Te-doped
GaAs epitaxial layer (free carrier concentration was
3.9×1015 cm�3 for the sample GAE1, 3.5×1015 cm�3 for
GAE2 and 5×1015 cm �3 for GAE3) grown on monocrystal
Te-doped GaAs substrate ( 318 ñm102 −×=n ). The thick-
nesses of the layer and the substrate were 6 and 300 µm,
respectively.
3) The GaAs:Te epitaxial n-n+ structures with a buffer
layer. The layer, 1 µm thick, 316 cm108 −×=n , and the
layer, 2 µm thick, 315 cm107 −×=n , grown consistently
on (100) GaAs substrate ( 318 cm102 −×=n ). The GAB1
and GAB2 samples are made from different wafers.
All investigated epitaxial structures were fabricated
using the industrial vapor phase epitaxy method and pos-
sessed standard technical characteristics.
Samples were irradiated in free space at the room tem-
perature using magnetron radiation. The microwave fre-
quency was 2.45 GHz, the specific power density was
1.5 W/cm2. The total treatment time was 20 to 60 seconds
for different samples; the influence continuous duration
was 5�10 s to avoid sample heating.
The parameters of deep centers (the electron capture
cross section nσ and the energy depth of the electron trap
level counted from the edge of conductivity band
)( tC EE − ) have been determined before and after the
microwave treatment. The method of acoustoelectric tran-
O.Ya. Olikh: Acoustoelectric transient spectroscopy of microwave ...
451SQO, 6(4), 2003
sient spectroscopy is used [8,9]: the GaAs samples are
placed by the epitaxial layer on the piezoelectric plate
( 3LiNbO � see Fig.1); during propagation of acoustic
waves in the plate, the direct transverse acoustoelectric
voltage (TAV) arose in semiconductor samples. After an
ultrasonic impulse ending, TAV decreased to zero. This
decrease can be interpolated by the exponential func-
tion; the characteristic relaxation time τ is known to be
determined by parameters of the deep level, located in
the near-surface region [8,10]:
( ) ( )( )kTEEN tCcTn −= − exp1υστ (1)
where υT represents the free electron thermal velocity; Nc
is the effective density of states at the bottom of the con-
ductivity band. The experimental measuring of TAV ki-
netic at different temperatures allowed to define depend-
ence τ(T). The angle of the declination of a plot ln(τ) on
( ) 1−kT allowed to determine )( tC EE − and then to cal-
culate σn by using the equation (1).
Our measurements were carried out in the tempera-
ture range 290 to 350 K except for GAB1 and GAB2; for
these samples TAV appeared after sample heating up to
310 K only.
3. Experimental results and discussion
Fig. 2 represents the typical τ temperature dependencies
for the two samples before and after MW irradiation. It
is visible, that both the plot slopes (related to )( tC EE − )
and the characteristic relaxation time value changed af-
ter the microwave treatment. The other samples depend-
encies are similar; all results are presented in the Table.
The obtained results have some features. At first, the
irradiation influence on the carrier trapping cross sec-
tion is considerably stronger than the influence on the
energy level position. It is confirmed by σn can change
value by an order as well as, for example, by )( tC EE −
did not change practically, while σn increased by a factor
of 4 approximately at GAB1 after 20 s MW influence. Secondly, the irradiation dose for a substantial center
parameters changing for the epitaxial structures is higher
than for monocrystalline samples: it is possible to com-
pare results for the samples of the GA-set and GAB-set
after 20 s irradiation. After the repeated 20 s irradiation
of the GA sample, the TAV signal diminished consider-
ably and exceed the measuring range. It correlates with
data obtained in [7]; this work reports of the decrease in
the concentration of the centers with energy level at the
forbidden band top half due to microwave annealing.
Thirdly, the changes character at the monocrystalline
wafers and at the epitaxial structures is different:
)( tC EE − and σn decrease in monocrystals and increase
at structures with a buffer layer as well as without it.
Finally, the MW stimulated changes degree depend on
the free carrier concentration. It is possible to compare
results for the GA1 and GA2; these samples differ by the
free carrier concentration value only.
It should be noted that although the GaAs levels sub-
jacent a conductivity band bottom on 0.25, 0.31, 0.33,
t−t
t
t
exp (
TAV
)
V
GaAs
LiNbO3
Fig. 1. System for TAV signal measurements. Shown in the insert
is the time dependence of the pulse high-frequency (2.6 MHz)
voltage V for existing of with ultrasound in the piezoelectric
plate and the resulting TAV signal.
36 38 40
�8.5
�8.0
�7.5
a
( )kT
�1 �1, eV
1
2
ln
t
33 34 35 36
�8.0
�7.5
�7.0
�6.5
�6.0
�5.5
b
1
2
3
( )kT
�1 �1, eV
ln
t
Fig. 2. Temperature dependence of the characteristic TAV re-
laxation time for the samples GAE2 (a) and GAB1 (b). The
curve 1 corresponds to the unirradiated samples, curves 2�3 � to
the irradiated samples. The microwave treatment time is 20 s
(curve 2, b), 40 s (curve 3, b), 60 s (curve 2, a).
452
SQO, 6(4), 2003
O.Ya. Olikh: Acoustoelectric transient spectroscopy of microwave ...
0.43 eV and having a small trapping cross section
(10�16÷10�18 cm2) are known in literature (for example,
see [11]), but the levels exact atomic configuration is not
investigated; they are assumed to relate to the point de-
fects containing an impurity atom. The level (EC � Et) =
= (0.40÷0.42) eV and σn = (10�15÷10�16) cm2 is usually
assigned to the configuration VGa � VAs (EL5 center)
[12, 13] .
On our opinion, the changes of the deep level param-
eters are related to the structural-impurity alteration of a
semiconductor near-surface region, caused by microwave
treatment. Such alteration is earlier found out in [5-7].
Namely, according to [5,7], defects are gettered in a
material surface layer after this MW irradiation. The
charged defects concentration increase must result in the
electric field strength increase in this region. Simultane-
ously, the capture cross section of the levels EC � 0.33 eV,
EC � 0.31 eV and σn = (10�17÷10�18) cm2 is known [11] to
decrease when the electric field increase. The cross sec-
tion decrease is observed for the samples GA1-3. If the
free carrier concentration is higher, than the charged
defect screening is more effective and, consequently, the
change of GA1 (n = 1018 cm�3) is less significant than that
of GA2 (n = 1016 cm�3). In addition, the samples with
high resistance have the larger �skin-depth� of the mi-
crowave penetration [14]. The microwave induced in-
crease of the surface curvature radius and the internal
mechanical strain relaxation of n-n+-GaAs structure near-
surface layers were observed in [5]. It takes place due to
the separate dislocation origin and their diffusion along
sliding planes toward structure depth. Thus, the chang-
ing of value of the both electric and mechanical field in-
tensity take place in the near-surface region, and it, on
our opinion, results in the deep level alteration and pa-
rameter changing. And, if the changes take place due to
the linear and point defects spatial moving, then the mi-
crowave influence must depend on crystal orientation (see
GA1 and GA3, for example).
It is considered in [8,9] that the trap TAV appearance
in the epitaxial structures relates to centers at the inter-
nal epilayer-substrate boundary (internal surface). The
monocrystal TAV is caused by the defects at the external
surface. On our point of view, it is this spatial location
difference that is the reason of the MW induced changes
character difference (point defects move from sample
depth toward external surface, dislocation to opposite
side) as well as dose the dependence difference for the
epitaxial and monocrystalline wafers.
4. Conclusions
The microwave irradiation influence on the electron cap-
ture cross section and the energy level of centers in the
forbidden gap of n-GaAs monocrystal and n-GaAs-based
epitaxial structures has been investigated for the first time.
It was found that the deep level parameters are modified,
and the character of changes is different for monocrystals
and epitaxial structures. The observed changes is likely
to be due to gettering the defects in the material surface
layer and internal stress relaxation induced by the mi-
crowave treatment applied.
Acknowledgement
The author would like to thank Prof. R.V. Konakova for
helpful discussions.
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Table. Parameters of deep levels in GaAs structures before and
after the microwave treatment.
Sample Total time (EC � Et), eV σn
*, cm2
of microwave
treatment, s
GA1 0 0.31 3×10�17
20 0.30 2×10�17
GA2 0 0.33 4×10�17
20 0.28 6×10�18
GA3 0 0.49 5×10�14
20 0.4 2×10�15
GAE1 0 0.24 2×10�18
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GAE2 0 0.25 2×10�18
60 0.30 2×10�17
GAE3 0 0.43 8×10�17
60 0.46 7×10�16
GAB1 0 0.39 1×10�17
20 0.39 4×10�17
40 0.43 1×10�16
GAB2 0 0.40 1×10�16
20 0.41 1×10�16
40 0.45 4×10�16
*T=300 K for samples GA1�GA3, GAE1�GAE3, and
Ò=340 Ê for GAB1 and GAB2
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