Ultra-high field transport in GaN-based heterostructures
This paper describes measurements of the velocity of electrons at electric fields up to 100 kV/cm in GaN/AlGaN heterostructures. In order to avoid the Joule heating effect, a pulse technique with a time sweep of 10-30 ns was used. The experimental results indicate that overheating of the 2DEG does n...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2006
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| Cite this: | Ultra-high field transport in GaN-based heterostructures / S.A. Vitusevich, S.V. Danylyuk, B.A. Danilchenko, N. Klein, S.E. Zelenskyi, E. Drok, A.Yu. Avksentyev, V.N. Sokolov, V.A. Kochelap, A.E. Belyaev, M.V. Petrychuk, H. Luth // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 3. — С. 66-69. — Бібліогр.: 8 назв. — англ. |
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| author | Vitusevich, S.A. Danylyuk, S.V. Danilchenko, B.A. Klein, N. Zelenskyi, S.E. Drok, E. Avksentyev, A.Yu. Sokolov, V.N. Kochelap, V.A. Belyaev, A.E. Petrychuk, M.V. Luth, H. |
| author_facet | Vitusevich, S.A. Danylyuk, S.V. Danilchenko, B.A. Klein, N. Zelenskyi, S.E. Drok, E. Avksentyev, A.Yu. Sokolov, V.N. Kochelap, V.A. Belyaev, A.E. Petrychuk, M.V. Luth, H. |
| citation_txt | Ultra-high field transport in GaN-based heterostructures / S.A. Vitusevich, S.V. Danylyuk, B.A. Danilchenko, N. Klein, S.E. Zelenskyi, E. Drok, A.Yu. Avksentyev, V.N. Sokolov, V.A. Kochelap, A.E. Belyaev, M.V. Petrychuk, H. Luth // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 3. — С. 66-69. — Бібліогр.: 8 назв. — англ. |
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| container_title | Semiconductor Physics Quantum Electronics & Optoelectronics |
| description | This paper describes measurements of the velocity of electrons at electric fields up to 100 kV/cm in GaN/AlGaN heterostructures. In order to avoid the Joule heating effect, a pulse technique with a time sweep of 10-30 ns was used. The experimental results indicate that overheating of the 2DEG does not exceed 1000 K in this electric field range and drift velocity as high as ~10⁷ cm/s was obtained. Additionally, the low frequency 1/f noise spectra measured for a different bias voltage are analyzed with respect to field-induced contribution of hopping conductivity in AlGaN barrier region.
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 3. P. 66-69.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
66
PACS 72.20.Ht, 72.80.Ey, 73.40.-c
Ultra-high field transport in GaN-based heterostructures
S.A. Vitusevich1,*, S.V. Danylyuk1, B.A. Danilchenko2, N. Klein1, S.E. Zelenskyi2, E. Drok2,
A.Yu. Avksentyev3, V.N. Sokolov3, V.A. Kochelap3, A.E. Belyaev3, M.V. Petrychuk1, H. Lüth1
1Institut für Schichten und Grenzflächen and CNI - Center of Nanoelectronic Systems for Information Technology,
Forschungszentrum Jülich, Jülich D-52425, Germany
2Institute of Physics, NAS of Ukraine, 03028 Kyiv, Ukraine
3V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, 03028 Kyiv, Ukraine
*Corresponding author: phone: +49-2461-612345; fax: +49-2461-612470
E-mail address: s.vitusevich@fz-juelich.de
Abstract. This paper describes measurements of the velocity of electrons at electric
fields up to 100 kV/cm in GaN/AlGaN heterostructures. In order to avoid the Joule
heating effect, a pulse technique with a time sweep of 10-30 ns was used. The
experimental results indicate that overheating of the 2DEG does not exceed 1000 K in
this electric field range and drift velocity as high as ~107 cm/s was obtained.
Additionally, the low frequency 1/f noise spectra measured for a different bias voltage
are analyzed with respect to field-induced contribution of hopping conductivity in
AlGaN barrier region.
Keywords: HEMT, TLM, 2DEG, hot electrons, 1/f noise.
Manuscript received 20.09.06; accepted for publication 23.10.06.
1. Introduction
Advantages of the GaN-based materials in comparison
to the GaAs are the higher intervalley separation and
larger optical phonon energy, resulting in larger drift
velocities at high electric fields. The latter is promising
for high frequency operation of GaN-based devices and
introduces novel hot electron relaxation mechanisms.
Therefore experimental and theoretical study of high
electric field transport in the nitride-based materials and
heterostructures are extremely important. In this
communication we present results of steady state and
pulse measurements of GaN/AlGaN heterostructures up
to ultra high electric fields accompanied by low
frequency noise measurements. Hot electron relaxation
processes are analyzed.
2. Experimental
The GaN/AlGaN (33 % Al) undoped heterostructures
(designed for high electron mobility transistor
application and grown by MOCVD on sapphire substrate
with AlN buffer layer) of 1.1 µm GaN and 23 nm
AlGaN covered with a 320 nm Si3N4 passivation layer
were investigated. The transmission line mode (TLM)
patterns of different channel lengths and of the 100 µm
channel width were fabricated with using standard
ohmic contact process. The distance between TLM
contacts varied as 1, 5, 10, 20, 25, and 35 µm. A room
temperature mobility of 1250 cm2/Vs and sheet carrier
density of 1.05×1013 cm−2 were obtained in the 2DEG of
the channel by means of the Van der Pauw method. The
contact resistance was measured in low-field (ohmic)
region and taken into account when calculating the
average electric field. The velocity-electric field
dependences in GaN/AlGaN heterostructures were
obtained by measurements of the current-voltage, I-V,
characteristics using nanosecond voltage pulses applied
to the sample. This pulse regime minimizes the self-
heating effects. The measurements were performed in
the temperature range 4 – 300 K.
3. Results and discussion
3.1. Low-field transport and low-frequency noise under
self-heating conditions
Under steady-state conditions investigation of transport
and noise properties should be carried out with taking into
account both hot electrons and self-heating effects due to
dissipated Joule electric power. The current-electric field
characteristics, I-E, measured in dc regime (Fig. 1), are
strongly nonlinear, although the considered electric field
range is still below the fields of well-developed hot-
electron regime expected from theoretical predictions [1].
The current noise spectra also reveal considerable
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 3. P. 66-69.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
67
0 2 4 6 8
0
50
100
150
∆Ish
∆Ihe
C
ur
re
nt
(m
A
)
Electric field (kV/cm)
Fig. 1. The result of calculation of I vs E for the device with the
channel length of 25 µm. Solid line is ohmic I-E curve, arrows
show current decrease due to hot-electron (∆Ihe) and self-heating
(∆Ish). Circles the are experimental data measured at 300 K.
100 101 102 103 104 105
10-12
10-11
10-10
10-9
I
4
8
7
6
5
3
2
1
E (kV / c m)
1 - 0.04
2 - 0.09
3 - 0.18
4 - 0.35
5 - 0.75
6 - 1.52
7 - 2.73
8 - 3.78
f ×
S
I /
I2
F r e q u e n c y ( H z )
Fig. 2. Spectra of the normalized current noise for different
values of the electric field E measured at T = 300 K for the
device with the channel length of 25 µm. The intermediate
region (I) between low- and high-frequency 1/f noise is
indicated for the curve 6.
0.0 0.1 0.2 0.3 0.4 0.5 0.6
0
50
100
150
200
Te
m
pe
ra
tu
re
ri
se
(K
)
Dissipated power (W)
Fig. 3. Dependence of the temperature rise ∆T due to Joule
heating on the dissipative power Pdis in the channel of the
25-µm length at the initial temperature T0 = 300 K.
deviation from a 1/f law predicted in the McWhorter
(fluctuations of concentration) [2] or Hooge (mobility
fluctuations) [3] models. The main feature of noise spectra
is an increase of the 1/f noise level in the low-frequency
range together with increasing of applied electric field as
shown in Fig. 2. Between the low- and high-frequency 1/f
spectral ranges (flat regions in Fig. 2) a transition region
(I) appears, which is characterized by a strong deviation
from the 1/f behavior. This region (I) is strongly
depending on applied electric field. It is remarkable that in
the high-frequency interval the normalized noise level is
independent of the applied voltage.
In view of the fact that the self-heating is present
together with electrical field simultaneously, the analysis
of the noise spectra demands separation of temperature
and field effects. To solve this problem, we formulate a
theoretical model based on (i) heat dissipation and heat-
transfer modeling in the device and (ii) self-consistent
solution of coupled nonlinear equations for the channel
current and temperature rise ∆T [4]. The results of
simulation for current are presented in Fig. 1. The
reasonable coincidence of calculated current to
experiment was reached when both contributions
(electric field and self-heating) were taken into account.
The calculated temperature raise ∆T versus the
dissipated power Pdis in conducting channel is shown in
Fig. 3. With respect to obtained results, the temperature
rise in noise experiment does not exceed 60 K at the
field 3.78 kV/cm. The latter result allows us to suppose
that electric field plays a decisive role in the current
noise growth in the region (I), Fig. 2. In assumption that
hoping conductivity is present [5], we introduce the
phenomenological expression for the current noise for a
fixed frequency that could be proportional to
−
−∆
kT
eVd
J 3exp~
ε
, (1)
where ε3 is the activation energy of the hoping
conductivity, e – electron charge, V – electric field, d –
average distance between nearest deep traps, T –
temperature.
An exponential dependence of 2ISf I× versus V
for two fixed frequencies of 5×103 and 1×104Hz is
clearly seen from Fig. 4 with a slope equal to ed / kT.
The slope allows to estimate the value of d to be about
5×10−6 cm. Such a value is reasonable for the undoped
AlGaN barrier layer and considered noise behavior
could be attributed to processes of hopping conductivity
though deep traps in the layer [5].
3.2. High-field transport and velocity of electrons
in GaN/AlGaN heterostructures
The investigation of high-field electron transport
requires minimization of self-heating by using pulse
techniques. In this case, we can study pure hot-electron
effects. To determine the electron velocity, v, we used
the relation v = I / enW, where I is the current flowing
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 3. P. 66-69.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
68
0 1000 2000 3000 4000
10-12
10-11
10-10
2
1
f x
S
I /
I
2
Electric field (V/cm)
Fig. 4. Dependences of the current noise on the electric field
for two fixed frequencies: 5×103(1) and 104 Hz (2).
10-3 10-2 10-1 100 101 102103
104
105
106
107
Fig. 5. Electron velocity for two TLM samples as a function
of the electric field. The open symbols correspond to L =
= 5 µm, T0 = 4.2 K. The solid symbols correspond to L =
= 10 µm, T0 = 300 K, the solid curve represents the calcu-
lated dependence.
0 50 100
0
250
500
750
El
ec
tro
n
te
m
pe
ra
tu
re
(K
)
Electric field (kV/cm)
Fig. 6. Electron temperature Te dependence on the electric
field. The circles are experimental data; the solid curve
represents an extrapolation to high electric fields.
0 2 4 6
10-9
10-8
10-7
10-6
E
ne
rg
y
re
la
xa
tio
n
ra
te
(W
/e
le
ct
ro
n)
1000 / Te (K
-1)
Fig. 7. Dependence of the electron energy relaxation rate Pe
(in W per electron) on the inverse electron temperature.
Circles are the experimental data, solid line is the fitting of
Eq. (2) with E =92 meV and the fitting parameter τ = 25 fs.
within a short pulse (10-30 ns) of applied voltage, e is
the electron charge, n is the carrier concentration and W
is the width of the conducting channel. This type of
measurement relies on the assumption that the carrier
concentration remains constant during the measurement
even of the electric field changes. The experimental v-E
curves (there E = V/L is the average electric field in the
conducting channel) measured on TLM with different
length are very similar. As it can be seen in Fig. 5, a
linear increase in the velocity up to the electric fields of
about 5 kV/cm is followed by a sub-linear dependence.
It is remarkable that despite our nitride structures have
relatively small low-field electron mobility (4000 and
1250 cm2/Vs at 4.2 and 300 K, respectively) we obtain
the magnitude of the drift velocity above 107 cm/s that is
very close to that predicted by the theory [1].
Because of the large carrier concentration, the
electron-electron (e-e) scattering dominates over other
relaxation mechanisms, and the shifted Maxwellian
function with an effective electron temperature Te and a
drift velocity provides good approximation for the
electron distribution [6]. Te can be estimated by the
“mobility comparison” method [7]. It is clearly seen in
Fig. 6, where experimental points are plotted together
with extrapolation toward high electric fields that even at
E = 100 kV/cm Te does not exceed 650 K. To analyze
the sources of the energy relaxation by electrically
heated electrons, we plotted the energy relaxation rate
per electron against the inverse electron temperature. It
is clearly seen from Fig. 7 that in the temperature range
250 K < Te < 500 K optical phonon emission is the
dominant energy relaxation process. In this case, the
standard expression for the electron energy relaxation
rate should be used [7]:
)exp( LOLO
e
e kT
P
ω
τ
ω
−= , (2)
where LOω is the LO phonon energy and
τ = (2αωLO)−1 is the electron−LO phonon scattering
Electric field (kV/cm)
D
rif
t v
el
oc
ity
(c
m
/c
)
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 3. P. 66-69.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
69
time, α is the Fröhlich coupling constant. In the
mentioned temperature range, the experimental data are
very close to the calculated ones with LOω = 92 meV,
which is well known, and τ = 25 fs as fitting parameter.
It should be noted out that the estimated values of Te are
much lower (at E = 90 kV/cm, Te estimated from our
experiments is about 600 K) then those determined by
measurements of the noise temperature, where for the
same value of the electrical field the noise electron
temperature Te is about 1150 K [8].
4. Conclusions
In this paper, we presented experimentally measured low
and high field transport phenomena for a two-
dimensional electron gas in GaN/AlGaN heterostructure.
Under steady-state conditions, investigation of transport
and noise properties have been carried out with taking
into account both hot electrons and self-heating effects
due to the dissipated Joule electric power. Noise
increasing with an applied voltage is assumed to be the
field induced hopping conductivity in AlGaN barrier.
In ultra short pulse regime, we obtained the
magnitude of the drift velocity above 107 cm/s that is
very close to that predicted by the theory. Estimation of
thermal budget of the system shows that overheating of
the 2DEG does not exceed 650 K up to electric fields
about 100 kV/cm.
Acknowledgements
The authors would like to thank V. Tilak, J. Smart,
A. Vertiatchikh and L.F. Eastman (Cornell University)
for their collaboration in this study. This work is
supported by the Office of Naval Research under Grant
No. N00014-01-1-0828 (Project Monitor Dr. Colin
Wood) and by Deutsche Forschungsgemeinschaft
(project No. KL 1342/3). The work at Institute of
Semiconductor Physics in Kyiv was supported by CRDF
Project No. UE2-2439-KV-02 and Institute of Physics
by Ukrainian FFR Project F7/379.
References
1. E.A. Barry, K.W. Kim, V.A. Kochelap, Hot
electrons in group-III nitrides at moderate electric
fields // Appl. Phys. Lett. 80(13), p. 2317-9 (2002).
2. Sh. Kogan, Electronic noise and fluctuations in
solids. Cambridge University Press, Cambridge,
UK, 1996.
3. F.N. Hooge, T.G.M. Kleinpenning, L.K.J. Van-
damme, Experimental studies on 1/f noise // Repts
Progr. Phys. 44(5) p. 479-532 (1981).
4. S.A. Vitusevich, S.V. Danylyuk, N. Klein et al.,
Separation of hot-electron and self-heating effects
in two-dimensional AlGaN/GaN-based conducting
channels // Appl. Phys. Lett. 82(3), p. 748-750
(2003).
5. D.C. Look, D.C. Reynolds, W. Kim, O. Aktas,
A. Botchkarev, A. Salvador, and H. Morkoc, Deep-
center hopping conduction in GaN // J. Appl. Phys.
80(5), p. 2960-2963 (1996)
6. P. Tripathi, B.K. Ridley, Dynamics of hot-electron
scattering in GaN heterostructures // Phys. Rev. B
66(19), 195301-10 (2002).
7. N.M. Stanton, P. Hawker, A.J. Kent, T.S. Cheng,
and C.T. Foxon, Hot electron energy relaxation in
gallium nitride // Phys. status solidi (a) 176(1),
p. 369-372 (1999).
8. A. Matulionis, J. Liberis, I. Matulioniene et al.,
Hot-phonon temperature and lifetime in a biased
AlxGa1-xN/GaN channel estimated from noise
analysis // Phys. Rev. B 68(30) 035338-1-7 (2003) .
|
| id | nasplib_isofts_kiev_ua-123456789-121621 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1560-8034 |
| language | English |
| last_indexed | 2025-12-07T17:24:59Z |
| publishDate | 2006 |
| publisher | Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| record_format | dspace |
| spelling | Vitusevich, S.A. Danylyuk, S.V. Danilchenko, B.A. Klein, N. Zelenskyi, S.E. Drok, E. Avksentyev, A.Yu. Sokolov, V.N. Kochelap, V.A. Belyaev, A.E. Petrychuk, M.V. Luth, H. 2017-06-15T03:10:37Z 2017-06-15T03:10:37Z 2006 Ultra-high field transport in GaN-based heterostructures / S.A. Vitusevich, S.V. Danylyuk, B.A. Danilchenko, N. Klein, S.E. Zelenskyi, E. Drok, A.Yu. Avksentyev, V.N. Sokolov, V.A. Kochelap, A.E. Belyaev, M.V. Petrychuk, H. Luth // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 3. — С. 66-69. — Бібліогр.: 8 назв. — англ. 1560-8034 PACS 72.20.Ht, 72.80.Ey, 73.40.-c https://nasplib.isofts.kiev.ua/handle/123456789/121621 This paper describes measurements of the velocity of electrons at electric fields up to 100 kV/cm in GaN/AlGaN heterostructures. In order to avoid the Joule heating effect, a pulse technique with a time sweep of 10-30 ns was used. The experimental results indicate that overheating of the 2DEG does not exceed 1000 K in this electric field range and drift velocity as high as ~10⁷ cm/s was obtained. Additionally, the low frequency 1/f noise spectra measured for a different bias voltage are analyzed with respect to field-induced contribution of hopping conductivity in AlGaN barrier region. The authors would like to thank V. Tilak, J. Smart, A. Vertiatchikh and L.F. Eastman (Cornell University) for their collaboration in this study. This work is supported by the Office of Naval Research under Grant No. N00014-01-1-0828 (Project Monitor Dr. Colin
 Wood) and by Deutsche Forschungsgemeinschaft (project No. KL 1342/3). The work at Institute of Semiconductor Physics in Kyiv was supported by CRDF Project No. UE2-2439-KV-02 and Institute of Physics by Ukrainian FFR Project F7/379. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics Ultra-high field transport in GaN-based heterostructures Article published earlier |
| spellingShingle | Ultra-high field transport in GaN-based heterostructures Vitusevich, S.A. Danylyuk, S.V. Danilchenko, B.A. Klein, N. Zelenskyi, S.E. Drok, E. Avksentyev, A.Yu. Sokolov, V.N. Kochelap, V.A. Belyaev, A.E. Petrychuk, M.V. Luth, H. |
| title | Ultra-high field transport in GaN-based heterostructures |
| title_full | Ultra-high field transport in GaN-based heterostructures |
| title_fullStr | Ultra-high field transport in GaN-based heterostructures |
| title_full_unstemmed | Ultra-high field transport in GaN-based heterostructures |
| title_short | Ultra-high field transport in GaN-based heterostructures |
| title_sort | ultra-high field transport in gan-based heterostructures |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/121621 |
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