Influence of physical and geometrical parameters on electrical properties of short gate GaAs MESFETs
In the information sciences such as computer science, telecommunications, the treatment of signal or image transmission, the field effect components play an important role. In the frame of our work, we are interested in the study of the gallium arsenide short gate field effect transistor called GaAs...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
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| Zitieren: | Influence of physical and geometrical parameters on electrical properties of short gate GaAs MESFETs / S. Khemissi, N. Merabtine, M. Zaabat, C. Kenzai, Y. Saidi, S. Amourache // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 2. — С. 34-39. — Бібліогр.: 9 назв. — англ. |
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irk-123456789-1214292017-06-15T03:03:56Z Influence of physical and geometrical parameters on electrical properties of short gate GaAs MESFETs Khemissi, S. Merabtine, N. Zaabat, M. Kenzai, C. Saidi, Y. Amourache, S. In the information sciences such as computer science, telecommunications, the treatment of signal or image transmission, the field effect components play an important role. In the frame of our work, we are interested in the study of the gallium arsenide short gate field effect transistor called GaAs MESFET. After analytical studying the component static characteristics, according to different operation regimes, a numerical simulation was worked out. The influence of technological dimensions (L, Z, a, and Nd) was studied. The obtained results allow us to determine optimal parameters of the devices from the viewpoint of their applications and specific use. 2006 Article Influence of physical and geometrical parameters on electrical properties of short gate GaAs MESFETs / S. Khemissi, N. Merabtine, M. Zaabat, C. Kenzai, Y. Saidi, S. Amourache // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 2. — С. 34-39. — Бібліогр.: 9 назв. — англ. 1560-8034 PACS 85.30.Tv http://dspace.nbuv.gov.ua/handle/123456789/121429 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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In the information sciences such as computer science, telecommunications, the treatment of signal or image transmission, the field effect components play an important role. In the frame of our work, we are interested in the study of the gallium arsenide short gate field effect transistor called GaAs MESFET. After analytical studying the component static characteristics, according to different operation regimes, a numerical simulation was worked out. The influence of technological dimensions (L, Z, a, and Nd) was studied. The obtained results allow us to determine optimal parameters of the devices from the viewpoint of their applications and specific use. |
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Khemissi, S. Merabtine, N. Zaabat, M. Kenzai, C. Saidi, Y. Amourache, S. |
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Khemissi, S. Merabtine, N. Zaabat, M. Kenzai, C. Saidi, Y. Amourache, S. Influence of physical and geometrical parameters on electrical properties of short gate GaAs MESFETs Semiconductor Physics Quantum Electronics & Optoelectronics |
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Khemissi, S. Merabtine, N. Zaabat, M. Kenzai, C. Saidi, Y. Amourache, S. |
| author_sort |
Khemissi, S. |
| title |
Influence of physical and geometrical parameters on electrical properties of short gate GaAs MESFETs |
| title_short |
Influence of physical and geometrical parameters on electrical properties of short gate GaAs MESFETs |
| title_full |
Influence of physical and geometrical parameters on electrical properties of short gate GaAs MESFETs |
| title_fullStr |
Influence of physical and geometrical parameters on electrical properties of short gate GaAs MESFETs |
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Influence of physical and geometrical parameters on electrical properties of short gate GaAs MESFETs |
| title_sort |
influence of physical and geometrical parameters on electrical properties of short gate gaas mesfets |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2006 |
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http://dspace.nbuv.gov.ua/handle/123456789/121429 |
| citation_txt |
Influence of physical and geometrical parameters on electrical properties of short gate GaAs MESFETs / S. Khemissi, N. Merabtine, M. Zaabat, C. Kenzai, Y. Saidi, S. Amourache // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 2. — С. 34-39. — Бібліогр.: 9 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
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2025-07-08T19:53:07Z |
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| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 34-39.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
34
PACS 85.30.Tv
Influence of physical and geometrical parameters
on electrical properties of short gate GaAs MESFETs
S. Khemissi2 , N. Merabtine1 , M. Zaabat3 , C. Kenzai 4, Y. Saidi 4, S. Amourache4
1Laboratoire Electromagnetisme et Telecommunication, Electronics department,
Faculty of Engineering, University Mentouri Constantine, Algeria
E-mail: na_merabtine@hotmail.com.
2Departement de Seti, Faculté de technologie, Université de khenchla, Algeria
E-mail: saadekhemissi@yahoo.fr
3Physics department, University of Oum-El-Bouaghi, Algeria
E-mail: Zaabat@hotmail.com.
4Laboratoire des couches minces et interfaces, Département de physique, Faculté des Sciences,
Université Mentouri de Constantine, Algeria
E-mail: musbelgat@yahoo.fr
Abstract. In the information sciences such as computer science, telecommunications, the
treatment of signal or image transmission, the field effect components play an important
role. In the frame of our work, we are interested in the study of the gallium arsenide short
gate field effect transistor called GaAs MESFET. After analytical studying the
component static characteristics, according to different operation regimes, a numerical
simulation was worked out. The influence of technological dimensions (L, Z, a, and Nd)
was studied. The obtained results allow us to determine optimal parameters of the
devices from the viewpoint of their applications and specific use.
Keywords: GaAs MESFET, technological, physical and geometrical parameters,
parasite elements.
Manuscript received 09.01.06; accepted for publication 29.03.06.
1. Introduction
Several research laboratories showed the interest of
using the Gallium Arsenide Field Effect Transistor
(GaAs MESFET) for the realization of analog and logic
integrated circuits. A fairly good technological
realization can only be achieved with a deep knowledge
of the component physics and all the intrinsic and
extrinsic phenomena that can limit its performances. In
this paper, we propose an analytical model (simulation)
of current-voltage characteristics of a short gate GaAs
MESFET, then we have elaborated a software that
enable us to solve the system of differential equations
and plot a series of different curves.
2. Determination of the voltage under the gate
The two dimensional solution of differential equations
using the Green method gives a distribution of the
electric field under the region of the space charge area
(SCA).
To calculate the voltage under the gate, the SCA is
divided in two main regions [1].
• The region (1) directly under the gate,
considered as a region controlled by the gate. We use the
uni-dimensional approximation to calculate the
component of the expression for the voltage Vq(x, y)
specific to this region.
• The region (2) outside the first region
considered to be uncontrolled by the gate. The two-
dimensional voltage of the channel under the gate is
given as follows:
Vc (x, y) = Vq (x, y) + Vl (x, y). (1)
Where
∫
∫
−++
+=
)(
0
),(
),(),(
xh
y
gbi
d
y
d
q
VVdyyxeNy
ydyyxeNyxV
ε
ε
(2)
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 34-39.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
35
and
( )
( )
( )
( ) ( )yk
Lk
xkA
Lk
xLkAyxV
d
s
l
1
1
1
1
1
1
1
sin
sinh
sinh
sinh
)(sinh),(
⎥
⎦
⎤
+
⎢
⎣
⎡
+
−
=
(3)
with
[ ]∫ −=
a
qc
s dyykyVyV
a
A
0
11 )sin(),0(),0(2 (4)
and
[ ]∫ −=
a
qc
d dyykyLVyLV
a
A
0
11 )sin(),(),(2 . (5)
dA1 and SA1 are the Fourier coefficients for the gate
supplementary for voltage drain and source sides,
respectively, [1]
and
a
k
2
π
1 = .
From (3) and (4) the total voltage expression is
written as:
∫ +−+=
)(
0
),(),(),(
xh
bigl
d
c VVyxVydyyxeNyxV
ε
. (6)
3. Effect of the mobility law
The constant mobility hypothesis and independent of the
electric field in the n-type GaAs cannot convey the
physical phenomena. The analytical expression of the
variations of the mobility with the electric field which
we use is a simplified relation [2-4] given as follows:
• for the weak electric field where E < E0
µ = µ0 , (7a)
• for the high electric field beyond E0 (E > E0)
2/12
0
0
1
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ −
+
=
sE
EE
μμ . (7b)
This mobility law allows us to obtain the different
expressions of the drain current in different operation
regimes.
4. Current-voltage characteristics
To calculate the drain current expression as a function of
the drain voltage for different values of the gate voltage,
we use the following hypothesis:
• we neglect the current along the Y axis [5], this
approximation is valid for the short gate components;
• we suppose the electron mobility to be variable
according to the zones under the gate;
• we derived the channel in three regions
according to the electric field value (Fig. 1) [6, 7].
The Id (Vd, Vg) characteristics of the GaAs
MESFET transistor corresponding to different operation
regimes are ruled by the following equations.
4.1. Linear regime
This regime exists as far as La occupies whole channel, it
corresponds to weak field sphere where the mobility is
equal to µ0.
The drain current expression in this regime is given
as:
,
3
2
3
2
3
2
2/3
2/3
⎥
⎥
⎥
⎦
⎤
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ −
+
+
⎢
⎢
⎢
⎣
⎡
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ −+
−=
p
gbi
p
gbid
p
d
pld
V
VV
V
VVV
V
V
II
(8)
where
a
d
pl L
aZNe
I
ε
μ
2
3
0
22
= .
4.2. Pinch-off regime
As the drain voltage increases, the electric field in the
channel increases beyond E0.Then the channel under the
gate presents two regions.
One region with the length La in which the field is
inferior to E0 and the electron mobility is constant and
given by µ = µ0. The other region with the length Lb (L =
= La + Lb) in which the field is superior to the field E0,
but inferior to the field Em and the electron mobility is
given by the expression (7b).
La Lb Lc
Substrate S-I
S Grille D
Fig. 1. Active zone repartions according to the electrical field
variation.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 34-39.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
36
Table 1.
Transistor L(μm) A(μm) Z(μm) μ0(m2/Vcm) Nd (1023/m) Vs(m/s) Vbi(V) Vp(V)
MESFET 1 1 0.153 300 0.4000 1.17 3.6 103 0.85 1.93
MESFET 2 0.5 0.1435 300 0.4000 1.31 7.3 103 0.85 1.93
First region: for E < E0 and 0 < x < La
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ −
−⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ −+
−=
2/32/3
3
2
3
2
p
gbi
p
gbiad
p
da
d
pl
a V
VV
V
VVV
V
V
I
LI
L
(9)
Second region: for: E0 < E < Em and La < x < L
,
3
2
2/3
2/3
⎥
⎥
⎥
⎦
⎤
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ −+
+
+
⎢
⎢
⎢
⎣
⎡
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ −+
−
−
=
p
gbida
p
gbid
p
dad
d
ps
b
V
VVV
V
VVV
V
VV
I
LI
L
(10)
where
2/12
01
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ −
+
=
s
p
ps
E
EE
I
I .
4.3. Saturation regime
In this case, the channel under the gate is divided into
three regions La, Lb and Lc where L = La + Lb + Lc,
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ −
−⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ −+
−=
2/32/3
3
2
3
2
p
gbi
p
gbida
p
da
d
pl
a V
VV
V
VVV
V
V
I
LI
L , (11)
,
3
2
3
2
2/32/3
⎥
⎥
⎥
⎦
⎤
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ −+
+⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ −+
−
⎢
⎢
⎣
⎡
−
−
=
p
gbida
p
gbidm
p
dadm
d
ps
b
V
VVV
V
VVV
V
VV
I
LI
L
(12)
,
3
2
3
2
2/3
2/3
⎥
⎥
⎥
⎦
⎤
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ −+
+
⎢
⎢
⎢
⎣
⎡
+⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ −+
−
−
=
p
gbidm
p
gbid
p
dmd
d
ps
c
V
VVV
V
VVV
V
VV
I
LI
L
(13)
where Vda and Vdm are successively maxima and pinch-
off voltages for linear regimes.
5. Effect of parasite elements
The characteristics that we have presented are those
concerning internal or intrinsic dimensions (Id, Vd, Vg).
To obtain the external or extrinsic characteristics (Ids,
Vds, Vgs) of the component we have to take into
consideration the effect of the parasite access source
resistance Rs, the drain resistance Rd as well as the effect
of the resistance Rp parallel to the channel on the
polarization voltages values.
To obtain the real expressions of the characteristics
Ids (Vds, Vgs), we have to substitute the intrinsic terms by
the extrinsic terms in all the previous relations.
Therefore:
Vd = Vds + Vld – (Rs + Rd) Id , (14a)
Vg = Vgs + Vls – Rs Id , (14b)
Id = Ids – (Vd / Rp) . (14c)
6. Results and discussion
In order to validate the I-V characteristics of the GaAs
MESFET set up in the previous work, a simulation
software based on different formulas and equations is
used as well as the obtained results and their discussions.
6.1. Simulation software
The simulation software is realized with FORTRAN 32,
version 01, from the expressions obtained in the
previous paragraphs. It allows the resolution of equation
systems and the edition of the results in specific files [8].
With this software we are able to determine:
• the current-voltage characteristics in different
operation regimes;
• the effect of parasite resistances on the current-
voltage characteristics;
• the effect of Vls and Vld voltages on the current-
voltage characteristics;
• the effect of geometrical and technological
parameters (L, a, Z, and Nd) on the current-voltage
characteristics.
6.2. Current-voltage characteristics
The numerical calculations (Fig. 2) of the drain current
as a function of the polarization voltage was carried out
by the expressions (8)-(13) previously derived.
The study was carried out on two transistors
MESFET 1 and MESFET 2, parameters of which are
gathered in Table 1.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 34-39.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
37
Declaration of parameters
Introduction of the parameters a, Z, L, Nd, ε0, εGaAs, µ0, Vbi, Vs, Em, E0, Rs, Rd, Rp,
Introduction of the expressions of Vp and Ip
J = 0
Vg = −J
Introduction of the expressions of Vda and Vds
I = 0
Vd = I
Calculation of expressions of the side voltages Vls and Vld
Calculation of the mobility and velocity
Calculation of the general expression of I-V
Vd ≤ Vda
Calculation of the expression of I-V
in the linear regime
Yes
Vd ≤ Vds
Calculation of the expression of I-V
in the pinch-off regime
Calculation of the expression
of I-V in the saturation regime
Vds = Vd+(Rs+Rd)Id
Ids = Id +(Vd/Rp) Vds = Vd+(Rs+Rd) Id
Ids = Id +(Vd/Rp)
Vds = Vd+(Rs+Rd)Id
Ids = Id +(Vd/Rp)
Write Vgs, Vds, Ids
I = I + 1
I ≤ Imax J = J+1
J ≤ JEND
Yes
No
No
Yes
Write Vgs,Vds, Ids
Write Vgs, Vds, Ids
No
In Figs 3a and b, we have compared the measured
Ids (Vds, Vgs) characteristics and the calculated ones by
the simulation for the transistors MESFET 1 and
MESFET 2. In the linear regime, i.e., at weak drain
voltage polarization, we notice a good agreement
between the experimental values and the simulation ones
for both transistors. When the drain voltage increases
and becomes more important, we notice a certain gap
between the experimental values and the results of the
simulation. This gap progressively increases until the
saturation. This gap is mainly caused by the
approximations made in the mathematical model and
simulation software; it is also due to the geometric
parameter effects and the existence of parasitic quantum
phenomena that we have not taken into consideration. In
the saturation regime, when the drain voltage gets
important, we notice that the theoretical results are in
good agreement with the experimental ones. In conclu-
sion, we also remark that the theoretical and experi-
mental results have the same behavior towards the drain
voltage and coincide well, notably at high values of the
Vds voltage. This shows that the method is well founded.
6.3. Effect of source and drain parasite resistances
In order to put into evidence the effects of the source and
drain parasite resistances Rs and Rd on the characteristics
I-V of the GaAs MESFET, which we present in Figs 4a
and b, in the case of the previous two transistors, the
variations of the drain current as a function of the drain
voltage with and without the parasite resistance were
estimated.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 34-39.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
38
Fig. 3. Comparison of I-V measured and simulated
characteristics for MESFET 1 (a) and MESFET 2 (b).
Fig. 4. Effect of the parasite elements on the I-V
characteristics: resistances Rs and Rd (a) and side voltages Vls
and Vld (b).
Fig. 5. Current-voltage characteristic variations for the
transistors: MESFET 3 (a), MESFET 4 (b), MESFET 5 (c),
MESFET 6 (d).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 34-39.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
39
6.4. Effect of physical and geometrical parameters
In our numerical simulation [8, 9], we have studied the
influence of different physical and geometrical
parameters L (length of the gate), a (thickness of the
active layer), Z (width of the gate) and Nd (doping) on
the electrical characteristics of the GaAs MESFET
transistors, parameters of which are gathered in Table 2.
Figs 5a, b, c, and d show the drain current Ids
variations as a function of the drain voltage Vds for
different physical and geometrical parameters L, a, Z,
and Nd.
Table 2.
Transistor a1 b1 C1 Vl / Vp
MESFET 1 −0.10 0.10 0.05 0.01
MESFET 2 −0.14 0.10 0.04 0.01
7. General conclusion
In this paper, we have proposed an analytical study of
the current-voltage characteristics of the GaAs MESFET
using the simulation software. The influence of parasite
elements, physical and geometrical parameters on these
characteristics has been clearly established. The obtained
results allow the focusing of the components geometry
adapted to specific uses.
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8. S. Khemissi, Master thesis. Faculty of Sciences.
Constantine University, 2003.
9. N. Merabtine, Ph.D thesis. Faculty of Engineering.
Constantine University, 2003.
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