In–HgCdTe–In structures with symmetric nonlinear I–V characteristics for sub-THz direct detection
This paper reports on the development and investigations of In–Hg₁₋ₓCdxTe–In structures with symmetric nonlinear I–V curves that are sensitive to sub-terahertz radiation. It is shown that at low currents photoresponse of the detectors based on these structures is due to the presence of potential bar...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2017
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| Cite this: | In–HgCdTe–In structures with symmetric nonlinear I–V characteristics for sub-THz direct detection / N.I. Kukhtaruk, V.V. Zabudsky, A.V. Shevchik-Shekera, N.N. Mikhailov, F.F. Sizov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2017. — Т. 20, № 2. — С. 173-178. — Бібліогр.: 13 назв. — англ. |
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| author | Kukhtaruk, N.I. Zabudsky, V.V. Shevchik-Shekera, A.V. Mikhailov, N.N. Sizov, F.F. |
| author_facet | Kukhtaruk, N.I. Zabudsky, V.V. Shevchik-Shekera, A.V. Mikhailov, N.N. Sizov, F.F. |
| citation_txt | In–HgCdTe–In structures with symmetric nonlinear I–V characteristics for sub-THz direct detection / N.I. Kukhtaruk, V.V. Zabudsky, A.V. Shevchik-Shekera, N.N. Mikhailov, F.F. Sizov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2017. — Т. 20, № 2. — С. 173-178. — Бібліогр.: 13 назв. — англ. |
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| description | This paper reports on the development and investigations of In–Hg₁₋ₓCdxTe–In structures with symmetric nonlinear I–V curves that are sensitive to sub-terahertz radiation. It is shown that at low currents photoresponse of the detectors based on these structures is due to the presence of potential barriers at the contacts. The dependences of the photoresponse as a function of the bias current are measured at the radiation frequency ν = 140 GHz in the 77–300 K temperature range. The studied structures may be used as detectors of sub-terahertz radiation at room temperature or under weak cooling. The calculated NEP of investigated In–n-Hg₀.₆₁Cd₀.₃₉Te–In detectors was 3.5·10⁻⁹ W/Hz¹/², if taking into account thermal and shot noise.
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 2. P.173-178.
doi: https://doi.org/10.15407/spqeo20.02.173
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
173
PACS 07.57.Kp, 85.25.Pb
In–HgCdTe–In structures with symmetric nonlinear
I–V characteristics for sub-THz direct detection
N.I. Kukhtaruk1, V.V. Zabudsky1, A.V. Shevchik-Shekera1, N.N. Mikhailov2, F.F. Sizov1
1Institute of Semiconductor Physics, NAS of Ukraine,
41, prospect Nauky, 03028 Kyiv, Ukraine
E-mail: kukhtarukn@gmail.com
2Institute of Semiconductor Physics, SB of the RAS,
13, Lavrentiev av., Novosibirsk, 630090, Russia
E-mail: ifp@isp.nsc.ru
Abstract. This paper reports on the development and investigations of In–Hg1–xCdxTe–In
structures with symmetric nonlinear I–V curves that are sensitive to sub-terahertz
radiation. It is shown that at low currents photoresponse of the detectors based on these
structures is due to the presence of potential barriers at the contacts. The dependences of
the photoresponse as the function of the bias current are measured at the radiation
frequency ν = 140 GHz in 77–300 K temperature range. The studied structures may be
used as the detectors of sub-terahertz radiation at room temperature or under weak
cooling. The calculated NEP of investigated In–n-Hg0.61Cd0.39Te–In detectors was 3.5·10–
9 W/Hz1/2, if taking into account thermal and shot noise.
Keywords: indium–mercury cadmium telluride–indium structures, sub-THz detectors,
current-voltage characteristics..
Manuscript received 12.01.17; revised version received 12.04.17; accepted for
publication 14.06.17; published online 18.07.17.
1. Introduction
The radiation frequency range ν ~ 0.1…0.3 THz
sometimes called the sub-THz range has a number of
advantages including high bandwidth of communication
lines, high-resolution of radar systems, nonionizing
nature of the radiation, capability of radiation to
propagate through many non-conducting materials, etc.
[1]. As applications field of THz technology continue to
expand, demands for the compact, low cost, suitable for
manufacturing and meeting the specific requirements
THz and sub-THz detectors increase as well.
Since in this work, In–HgCdTe–In structures with
symmetric nonlinear current-voltage (I–V) charac-
teristics have been studied for detection of sub-THz
radiation, the comparison should be made with other
known detector structures with non-linear I–V charac-
teristics. Up to date, Schottky diodes occupy a special
place among the THz and sub-THz detectors, in
particular, due to their high operation speed. Schottky
detectors are one of the basic devices among the THz
ones due to their fast response. The response time is of
the order of <~10–11 s resulting a detection broad
bandwidth of heterodyne detectors in the range of
several gigahertz. Schottky barrier diode as a radiation
detector can operate in the mixer or direct detection
modes. In the direct detection mode, the Schottky diode
operates as a rectifying detector. Due to the nonlinearity
of the I–V characteristic, the high-frequency voltage
generated by the incident radiation results in appearance
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 2. P.173-178.
doi: https://doi.org/10.15407/spqeo20.02.173
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
174
of a DC component that is proportional to the power of a
signal. A feature of the Schottky diode as the electronic
device is that the semiconducting layer has two contacts
with metal, one of which is ohmic, and the second forms
a potential barrier. To obtain it, two different metals are
used or additional processing steps are applied, such as
changing the semiconductor surficial region
composition.
In [2], a new type sensing element based on a low-
barrier metal-semiconductor-metal structure with a
symmetrical I–V characteristic for the electromagnetic
radiation detectors was proposed. In [3], the
characteristics of the GaAs THz-detector based on
planar metal-semiconductor-metal structure were
presented. A feature of this detector is the absence of
ohmic contacts.
In this paper, we describe the results of photo-
response measurements of symmetrical In–HgCdTe–In
structures at 140 GHz incident radiation. This structure
forms two Schottky barriers and has sensitivity in the
sub-terahertz range. Current dependences of
photoresponse were measured. The voltage sensitivity
and noise-equivalent power were calculated at low bias
currents.
2. Sensitive structures based on Hg1–xCdxTe and their
electrical characteristics
The contact between metal and semiconductor can result
in the ohmic junction or the rectifying one. The
necessary condition for the achievement of a rectifying
junction is the presence of a depletion layer in the
semiconductor at the interface. The layer depleted of free
charge carriers occurs as a result of the electrons transfer
from semiconductor to metal during equilibrium state
establishing. The presence of a depletion layer causes
the energy bands bending, which results in formation of
an energy barrier for the electron flow from metal to
semiconductor. This barrier is called as the Schottky
barrier and sets properties of junction. The Schottky
barrier height (ΦB) for the contact between the metal and
n-type semiconductor is the difference between the
metal workfunction (Wm) and the semiconductor electron
affinity (χ) [4]:
χ−=Φ mB W . (1)
In the case of contact between the metal and p-type
semiconductor, the Schottky barrier height can be
calculated as follows:
( )χ−−=Φ mgB WE , (2)
where Eg is the bandgap of semiconductor.
The Schottky barrier is independent of the
semiconductor doping and is controllable by the choice
of materials. The Schottky barrier height determines the
rectifying characteristic of contact: the more a barrier
height is, the better rectification. If the surface state
density in semiconductor is low (Fermi level is not
pinned at the surface) χ < Wm and χ + Eg > Wm are the
conditions of the rectifying junction for n-type and p-
type semiconductor, respectively.
The surface state density for Hg1–xCdxTe (MCT)
grown using molecular beam epitaxy was determined in
[5], and its value was ~1011 eV–1cm–2. Assuming that the
surface state density varies slightly during processing,
the influence of surface states on the Schottky barrier
height can be neglected. In this case, the MCT-metal
contact type can be estimated by the metal workfunction.
The In workfunction value is 3.97 eV, while the
dependence of Hg1–xCdxTe electron affinity on the
composition x can by described by the following
empirical expression [6]
( ) ( )[ ]083.0,813.023.4, −−=χ TxETx g . (3)
The temperature and composition dependence of
the Hg1–xCdxTe energy gap is given by the expression
[7]:
,)21(1035.5
832.081.093.1302.0
4
32
Tx
xxxEg
−⋅+
++−+−=
−
(4)
where Eg is in eV, T in K.
The results of χ and χ + Eg calculations for Hg1–
xCdxTe in the range of x values between 0 and 1 are
shown in Fig. 1. As seen from the plots, the sum of the
MCT electron affinity and the value of band gap is
higher than the In-workfunction in the whole range of x,
while χ can be higher or lower than the In-workfunction,
depending on x. Thus, it can be expected to obtain the
Schottky barrier junction in the case of contact between
indium and p-type Hg1–xCdxTe in all range of x and n-
type Hg1–xCdxTe at x < ~0.4.
0,0 0,2 0,4 0,6 0,8 1,0
3,0
3,2
3,4
3,6
3,8
4,0
4,2
4,4
4,6
T=300 K
T=77 K
T=300 K
χ
an
d
χ+
Ε
g,
e
V
Alloy composition of Hg1-xCdxTe (x), mole fraction
T=77 K
3.97 eV
χ
χ+Εg
Fig. 1. Electron affinity χ and χ + Eg of Hg1–xCdxTe vs
composition x as calculated using the equations (3) and (4).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 2. P.173-178.
doi: https://doi.org/10.15407/spqeo20.02.173
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
175
In general, the barrier heights of metal-
semiconductor systems are determined by both the metal
workfunction and interface states. When the surface state
density is sufficiently high, then the Fermi level at the
interface is pinned by the surface states. In this case, the
barrier height is independent of the metal workfunction
and is determined entirely by the surface properties of
semiconductor [4]. Thus, the properties of contacts are
greatly influenced by the quality of surface preparation,
sputtering technology, etc. It is known that metal-MCT
contact can be ohmic, or it can form a potential barrier of
different heights depending on the MCT surface
composition, metal deposition technique, availability of
annealing, etc. [8].
Mercury cadmium telluride samples with indium
contacts were used for the studies. The composition of
the n-type MCT was selected in such a way that, in
accordance with approximation in Fig. 1, there was a
potential possibility of barrier forming at the contacts.
The structures based on n-type and p-type MCT
(x = 0.39 and 0.31, respectively) with indium contacts
were made from the epitaxial films Hg1–xCdxTe grown
using molecular beam epitaxy. Indium was deposited by
electrolytic deposition on the MCT film, from which the
passivation layer was preliminarily etched. Fig. 2 shows
the schematic drawing of the fabricated devices. The
indium contacts serve simultaneously as bow-tie
antennas. The structures of this type were investigated
earlier in the framework of hot-electron bolometer
theory [9], and it demonstrated sensitivity to radiation in
ν = 0.037…1.54 THz frequency range at temperatures
T ~70…300 K. However, during studying the electrical
characteristics and sensitivity of these structures to
radiation, we found that current-voltage characteristics
of some samples deviate from linear behavior even at
room temperature. In this case, their photoresponse as a
function of the bias current does not match the behavior,
predicted by the theory for hot-electron bolometer [9]
and observed experimentally in Hg1–xCdxTe structures
with ohmic contacts previously [10]. Some samples had
linear current-voltage characteristics at room tempera-
ture, but at liquid nitrogen temperature these charac-
teristics were significantly nonlinear. To our mind,
nonlinearity of I–V curves indicates formation of
potential barriers near the contacts between semi-
conductor and metal.
Fig. 3 shows current-voltage characteristics for
some In–n-Hg0.61Cd0.39Te–In samples at T = 293 K and
T = 77 K. The form of I–V curves at Т = 77 K indicates
that both contacts have potential barrier and the resulting
current-voltage characteristic consists of the reverse
currents from both of junctions. Investigated In–p-
Hg0.69Cd0.31Te–In structures demonstrates nonlinear
current-voltage characteristics for both T = 293 K and
77 K temperatures.
3. Results and discussion
The photoresponse of samples was measured using an
IMPATT diode as 140 GHz radiation source. The source
output power was measured using the Gentec-EO power
monitor M-Link with thermopile sensor THZ12D-3S-
VP, and it was 25 mW. The radiation source was
equipped with a horn antenna, and output signal was
modulated at f = 220 Hz frequency. System of teflon
lenses were used to focus radiation at the detector that
were fed from the constant current source Keithley 2400.
To measure the photo-response of the samples at low
temperatures, they were placed to a cryostat with the
teflon window. The photoresponse was measured with
SR830 Lock-In Amplifier.
At room temperature, the experimental dependence
of the photoresponse against current in HgCdTe detector
structures (x = 0.39) exhibits the almost linear character
(Fig. 4a) (in this case I–V curve is close to the linear one,
too). At T = 77 K, when the current-voltage
characteristics of samples deviate from linear behavior,
dependences of the photoresponse on current demonst-
rate complicated forms: there are local maxima of signal
in the low bias currents for both current directions, as
well as the multiple change in the signal sign (Fig. 4b).
For p-type samples, which current-voltage charac-
teristics are nonlinear at room temperature, the
experimental dependences of the photoresponse against
current are nonlinear as well.
It was supposed that the photoresponse observed in
samples with nonlinear I–V curve has components not
only from carrier heating mechanism as in hot-electron
bolometers but also from processes occurring at
Schottky contacts.
Fig. 2. Schematic drawing of In–Hg1–xCdxTe–In structure.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 2. P.173-178.
doi: https://doi.org/10.15407/spqeo20.02.173
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
176
-0,4 -0,2 0,0 0,2 0,4
-3
-2
-1
0
1
2
3
sample number
2
3
4
C
ur
re
nt
, m
A
Voltage, V
T=293 K
-0,5 0,0 0,5
-2,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
2,0
sample number
2
3
4
Voltage, V
C
ur
re
nt
, m
A
T=77 K
a b
Fig. 3. Current-voltage characteristics of In–n-Hg0.61Cd0.39Te–In structures for Т = 293 K (a) and T = 77 K (b) (hole concentration
is 7.69·1014 cm–3 at T = 77 K).
-1,5 -1,0 -0,5 0,0 0,5 1,0 1,5
-40
-30
-20
-10
0
10
20
30
T=293 K
sample number
2
3
4
P
ho
to
re
sp
on
ce
, μ
V
Current, mA
-2 -1 0 1 2
0
100
200
300 T=77 K
sample number
2
3
4
Current, mA
P
ho
to
re
sp
on
ce
, μ
V
a b
Fig. 4. Photoresponse of In–n-Hg0.61Cd0.39Te–In structures versus the bias current for Т = 293 K (a) and T = 77 K (b)
(Nn = 7.69·1014 cm–3 at T = 77 K).
The current responsivity of the non-linear detector
can be written as [11]
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
Δ+
Δ+
β=β
2
1
0 1
1 , (3)
where )1(
)2(
0 2
1
f
f
=β , )2(
)4(2
1 16 f
fA
=Δ ,
)1(
)3(2
2 8 f
fA
=Δ ,
)4()1( ff − are derivatives of the function )(VfI = .
Voltage V is superposition of the constant voltage V0 and
small alternating signal voltage: tAVV ω+= cos0 .
.
At a low value of the input signal, the current
responsivity of the detector is determined by the factor
)1(
)2(
0 2
1
f
f
=β .
The voltage responsivity of detector is equal to the
product of the current responsivity and its differential
resistance Rd:
dR⋅β=γ . (4)
At a small magnitude of the signal
dR⋅β=γ 00 . (5)
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 2. P.173-178.
doi: https://doi.org/10.15407/spqeo20.02.173
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
177
-1,0 -0,5 0,0 0,5 1,0
-1,0
-0,5
0,0
0,5
1,0
V
ol
ta
ge
re
sp
on
si
vi
ty
, a
.u
.
Current, mA
measurement
calculation
-1,0 -0,5 0,0 0,5 1,0
-0,8
-0,4
0,0
0,4
0,8
V
ol
ta
ge
re
sp
on
si
vi
ty
, a
.u
.
Bias current, A
measurement
calculation
a b
Fig. 5. Calculated using Eq. (5) and measured voltage responsivity versus the sample bias current. (a) Т = 293 K, p-type MCT-
sample with х = 0.31. (b) T = 77 K, n-type MCT-sample with х = 0.39. The photoresponse is presented in arb. units to compare the
position of peaks.
Fig. 5 shows the measured and calculated voltage
responsivity of the investigated samples as a function of
the bias current. Calculations were performed using
Eq. (5) with the measured I–V curves of these samples.
At low currents, the obtained experimental dependences
of signal on the magnitude and direction of current
correlate with the calculated γ0 versus I curves, and it
indicates the dominant contribution of Schottky contacts
to the photoresponse of the structures under studying.
At low currents, main noises arising from the
Schottky barrier presence are the thermal and shot ones
related with the random motion of thermally agitated
electrons in the epilayer and from the fluctuations of the
number of electrons crossing the Schottky barrier,
respectively [12].
The thermal noise voltage from the device is
kTRVT 4= (6)
for one hertz bandwidth, where k is Boltzmann’s
constant, T – physical temperature, R – diode resistance
at a given voltage V = V0:
0
/ VVdIdVR
=
= . (7)
The mean squared value of the shot noise current is
eII sh 22 = (8)
for one hertz bandwidth, where e is the charge of
electron, I – average DC current. The shot noise voltage
from the device, without taken into account the space
charge depression factor, is
RIV shsh
2= . (9)
For the sample 4 (Fig. 4b) at I = 0.2 mA and T =
77 K, the thermal noise voltage is 1.6·10–9 V, the shot
noise voltage is 4.8·10–9 V.
The NEP is the signal level that produces a signal-
to-noise ratio of 1. It can be written in terms of
responsivity
V
noise
S
V
=NEP , (10)
where SV is the volt–watt responsivity.
Assuming that the antenna area is equal to the
maximum effective area GA
π
λ
=λ 4
2
[13] (where λ is the
radiation wavelength and G is the antenna gain), NEP at
current point I = 0.2 mA for the sample 4 in Fig. 4b is
3.5·10–9 W/Hz1/2 (the calculated value of G is equal to
0.4 for this MCT epitaxial structure and antenna design
at 140 GHz radiation frequency, the volt–watt
responsivity is equal to 1.42 V/W).
4. Conclusions
In this work, In–Hg1–xCdxTe–In structures with ohmic at
room temperature and non-ohmic at liquid nitrogen
temperature contacts that are caused by presence of
potential barriers at the contacts have been investigated.
At low currents, the photoresponse of detectors based on
these structures is due to the presence of potential
barriers at the contacts. At the low biases, the calculated
NEP of investigated In–n-Hg0.61Cd0.39Te–In detectors
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 2. P.173-178.
doi: https://doi.org/10.15407/spqeo20.02.173
© 2017, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
178
was 3.5·10–9 W/Hz1/2, when there available are the
thermal and shot noises. The presence of Schottky
barriers does not affect strongly on the NEP value, as
compared to the same structures that were investigated
in the framework of hot-electron bolometer theory
[9, 10].
Acknowledgements
This work was supported by Volkswagen Stiftung
Program and NASU program NANO №11/17H. We
would like to thank V.A. Petryakov for preparation of
contacts to the samples.
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| id | nasplib_isofts_kiev_ua-123456789-214937 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1560-8034 |
| language | English |
| last_indexed | 2026-03-21T13:45:10Z |
| publishDate | 2017 |
| publisher | Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| record_format | dspace |
| spelling | Kukhtaruk, N.I. Zabudsky, V.V. Shevchik-Shekera, A.V. Mikhailov, N.N. Sizov, F.F. 2026-03-04T12:54:31Z 2017 In–HgCdTe–In structures with symmetric nonlinear I–V characteristics for sub-THz direct detection / N.I. Kukhtaruk, V.V. Zabudsky, A.V. Shevchik-Shekera, N.N. Mikhailov, F.F. Sizov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2017. — Т. 20, № 2. — С. 173-178. — Бібліогр.: 13 назв. — англ. 1560-8034 PACS: 07.57.Kp, 85.25.Pb https://nasplib.isofts.kiev.ua/handle/123456789/214937 https://doi.org/10.15407/spqeo20.02.173 This paper reports on the development and investigations of In–Hg₁₋ₓCdxTe–In structures with symmetric nonlinear I–V curves that are sensitive to sub-terahertz radiation. It is shown that at low currents photoresponse of the detectors based on these structures is due to the presence of potential barriers at the contacts. The dependences of the photoresponse as a function of the bias current are measured at the radiation frequency ν = 140 GHz in the 77–300 K temperature range. The studied structures may be used as detectors of sub-terahertz radiation at room temperature or under weak cooling. The calculated NEP of investigated In–n-Hg₀.₆₁Cd₀.₃₉Te–In detectors was 3.5·10⁻⁹ W/Hz¹/², if taking into account thermal and shot noise. This work was supported by the Volkswagen Stiftung Program and the NASU program NANO №11/17H. We would like to thank V.A. Petryakov for the preparation of contacts to the samples. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics In–HgCdTe–In structures with symmetric nonlinear I–V characteristics for sub-THz direct detection Article published earlier |
| spellingShingle | In–HgCdTe–In structures with symmetric nonlinear I–V characteristics for sub-THz direct detection Kukhtaruk, N.I. Zabudsky, V.V. Shevchik-Shekera, A.V. Mikhailov, N.N. Sizov, F.F. |
| title | In–HgCdTe–In structures with symmetric nonlinear I–V characteristics for sub-THz direct detection |
| title_full | In–HgCdTe–In structures with symmetric nonlinear I–V characteristics for sub-THz direct detection |
| title_fullStr | In–HgCdTe–In structures with symmetric nonlinear I–V characteristics for sub-THz direct detection |
| title_full_unstemmed | In–HgCdTe–In structures with symmetric nonlinear I–V characteristics for sub-THz direct detection |
| title_short | In–HgCdTe–In structures with symmetric nonlinear I–V characteristics for sub-THz direct detection |
| title_sort | in–hgcdte–in structures with symmetric nonlinear i–v characteristics for sub-thz direct detection |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/214937 |
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