Carrier transport mechanisms in InSb diffusion p-n junctions
The linearly-graded p-n junctions were prepared by diffusion of cadmium into n-InSb(100) substrate with the electron concentration n ~ 1.6*10¹⁵ cm⁻³ at the temperature T = 77 K. Passivation and protection of mesa structures have been carried out using thin films of CdTe. Forward and reverse curre...
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Sukach, A. Tetyorkin, V. Voroschenko, A. Tkachuk, A. Kravetskii, M. Lucyshyn, I. 2017-05-30T10:21:08Z 2017-05-30T10:21:08Z 2014 Carrier transport mechanisms in InSb diffusion p-n junctions / A. Sukach, V. Tetyorkin, A. Voroschenko, A. Tkachuk, M. Kravetskii, I. Lucyshyn // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2014. — Т. 17, № 4. — С. 325-330. — Бібліогр.: 25 назв. — англ. 1560-8034 PACS 73.40.Kp, 73.40.Gk https://nasplib.isofts.kiev.ua/handle/123456789/118416 The linearly-graded p-n junctions were prepared by diffusion of cadmium into n-InSb(100) substrate with the electron concentration n ~ 1.6*10¹⁵ cm⁻³ at the temperature T = 77 K. Passivation and protection of mesa structures have been carried out using thin films of CdTe. Forward and reverse current-voltage characteristics were investigated within the temperature range 77…156 K. It has been found that the total dark current consists of generation-recombination and tunneling current components, which are dominant at high (T = 120…156 K) and low (T < 120 K) temperatures, respectively. Experimental results have been explained using the model of a nonhomogeneous p-n junction. It has been shown that in the linearly-graded p-n junction with the rather thick (~1 m) depletion region tunneling current flows through the states related to dislocations in the depletion region. The performed estimation of electrical parameters of diffusion InSb p-n junctions allows to predict behavior of InSb-based photodiodes at operation temperatures T > 77 K. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics Carrier transport mechanisms in InSb diffusion p-n junctions Article published earlier |
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Carrier transport mechanisms in InSb diffusion p-n junctions |
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Carrier transport mechanisms in InSb diffusion p-n junctions Sukach, A. Tetyorkin, V. Voroschenko, A. Tkachuk, A. Kravetskii, M. Lucyshyn, I. |
| title_short |
Carrier transport mechanisms in InSb diffusion p-n junctions |
| title_full |
Carrier transport mechanisms in InSb diffusion p-n junctions |
| title_fullStr |
Carrier transport mechanisms in InSb diffusion p-n junctions |
| title_full_unstemmed |
Carrier transport mechanisms in InSb diffusion p-n junctions |
| title_sort |
carrier transport mechanisms in insb diffusion p-n junctions |
| author |
Sukach, A. Tetyorkin, V. Voroschenko, A. Tkachuk, A. Kravetskii, M. Lucyshyn, I. |
| author_facet |
Sukach, A. Tetyorkin, V. Voroschenko, A. Tkachuk, A. Kravetskii, M. Lucyshyn, I. |
| publishDate |
2014 |
| language |
English |
| container_title |
Semiconductor Physics Quantum Electronics & Optoelectronics |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| format |
Article |
| description |
The linearly-graded p-n junctions were prepared by diffusion of cadmium into
n-InSb(100) substrate with the electron concentration n ~ 1.6*10¹⁵ cm⁻³ at the
temperature T = 77 K. Passivation and protection of mesa structures have been carried
out using thin films of CdTe. Forward and reverse current-voltage characteristics were
investigated within the temperature range 77…156 K. It has been found that the total
dark current consists of generation-recombination and tunneling current components,
which are dominant at high (T = 120…156 K) and low (T < 120 K) temperatures,
respectively. Experimental results have been explained using the model of a
nonhomogeneous p-n junction. It has been shown that in the linearly-graded p-n junction
with the rather thick (~1 m) depletion region tunneling current flows through the states
related to dislocations in the depletion region. The performed estimation of electrical
parameters of diffusion InSb p-n junctions allows to predict behavior of InSb-based
photodiodes at operation temperatures T > 77 K.
|
| issn |
1560-8034 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/118416 |
| citation_txt |
Carrier transport mechanisms in InSb diffusion p-n junctions / A. Sukach, V. Tetyorkin, A. Voroschenko, A. Tkachuk, M. Kravetskii, I. Lucyshyn // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2014. — Т. 17, № 4. — С. 325-330. — Бібліогр.: 25 назв. — англ. |
| work_keys_str_mv |
AT sukacha carriertransportmechanismsininsbdiffusionpnjunctions AT tetyorkinv carriertransportmechanismsininsbdiffusionpnjunctions AT voroschenkoa carriertransportmechanismsininsbdiffusionpnjunctions AT tkachuka carriertransportmechanismsininsbdiffusionpnjunctions AT kravetskiim carriertransportmechanismsininsbdiffusionpnjunctions AT lucyshyni carriertransportmechanismsininsbdiffusionpnjunctions |
| first_indexed |
2025-11-24T02:23:07Z |
| last_indexed |
2025-11-24T02:23:07Z |
| _version_ |
1850839999448088576 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 325-330.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
325
PACS 73.40.Kp, 73.40.Gk
Carrier transport mechanisms in InSb diffusion p-n junctions
A. Sukach1, V. Tetyorkin1, A. Voroschenko1, A. Tkachuk2, M. Kravetskii1, I. Lucyshyn1
1V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine,
41, prospect Nauky, 03028 Kyiv, Ukraine
2V. Vinnichenko Kirovograd State Pedagogical University, Kirovograd, Ukraine
Phone: 38 (044) 525-54-61, e-mail: teterkin@isp.kiev.ua
Abstract. The linearly-graded p-n junctions were prepared by diffusion of cadmium into
n-InSb(100) substrate with the electron concentration n 1.61015 cm–3 at the
temperature T = 77 K. Passivation and protection of mesa structures have been carried
out using thin films of CdTe. Forward and reverse current-voltage characteristics were
investigated within the temperature range 77…156 K. It has been found that the total
dark current consists of generation-recombination and tunneling current components,
which are dominant at high (T = 120…156 K) and low (T < 120 K) temperatures,
respectively. Experimental results have been explained using the model of a
nonhomogeneous p-n junction. It has been shown that in the linearly-graded p-n junction
with the rather thick (~1 m) depletion region tunneling current flows through the states
related to dislocations in the depletion region. The performed estimation of electrical
parameters of diffusion InSb p-n junctions allows to predict behavior of InSb-based
photodiodes at operation temperatures T > 77 K.
Keywords: infrared, InSb, linearly-graded junctions, dislocations, tunneling.
Manuscript received 19.01.14; revised version received 11.06.14; accepted for
publication 29.10.14; published online 10.11.14.
1. Introduction
InSb photodiodes are widely used for detection of
infrared radiation within the spectral range 3 to 5 m.
High structural perfection (low density of dislocations
and low-angle boundaries), uniformity and stability of
bulk InSb allow production of focal-plane arrays and
matrices [1-3]. Development of 2052×2052 InSb
photodiode matrix has been reported in [4]. The
photodiodes are usually produced by ion implantation of
beryllium, magnesium [5] or thermal diffusion of zinc
[2] and cadmium into n-InSb bulk substrates [1, 3, 4, 7].
Despite the fact that the development of high-quality
InSb photodiodes is known for a long time [5], the
problem of improving basic technical parameters and
characteristics remains valid until now [7-9]. Especially
important is to understand reasons of frequently observed
excess dark currents in the photodiodes, which lead to
worsening their performances. Availability of excess
current in a photodiode means that the measured current
can not be explained by bulk diffusion and the generation-
recombination carrier transport mechanism. For instance,
the excess current associated with the surface leakage was
observed at temperatures 77…110 K in the reverse-biased
planar InSb p+-n junctions [2]. Similarly, this current was
detected in mesa junctions at forward biases [10]. The
excess current in InSb photodiodes is ascribed to
tunneling [11, 12], trap-assisted tunneling [7] and
dislocations [13]. Note that in the cited works, except [2],
studies were performed at the fixed temperature 77 K. The
purpose of this paper is to study carrier transport
mechanisms in a wide temperature range. It is clear from
the above consideration is important from both scientific
and practical point of view.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 325-330.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
326
Table. Experimental and calculated parameters of InSb diffusion p-n junctions.
T, K I02, A β U0, mV ni, cm–3 W0, m τ0, s RS,
77 4·10–9 1.6 160 1.6·109 1.2 1.1·10–7 1.5
116 1.6·10–5 1.6 115 1.6·1012 1.1 2.5·10–8 1.7
134 2.6·10–4 1.6 90 1.1·1013 1.0 9.5·10–9 1.9
156 1.3·10–3 1.5 65 6.3·1013 0.9 9.8·10–9 2.1
Notes: U0 – current cutoff voltage, τ0 – carrier lifetime in the depletion region
2. Samples and experimental techniques
InSb p-n junctions were produced by diffusion of
cadmium into n-InSb monocrystalline substrates with the
(100) crystallographic orientation. The electron
concentration and mobility at T = 77 K were
1.61015 cm–3 and 6.4·105 cm2/V·s, respectively. The
surface damaged layer in substrates was removed by
chemical dynamic polishing using a polishing etchant
2% Br2 – 98% HBr. The quality of the polished surface
was controlled by an interference microscope and by
measuring its roughness. The average dislocation density
determined by selective etching was ~300 cm–2 [14].
Diffusion of Cd was carried out for 30 min using the
two-temperature method. The substrate and source
temperatures were ~400 and 380 ºC, respectively. To
prevent re-evaporation of components from the
substrate, an additional powder of Sb and In was loaded
into ampoule to ensure conditions of vapor saturation.
The thickness of the substrate was close to 500 m. The
depth of p-n junction was determined by measuring the
sign of thermo-emf during the layer-by-layer etching of
p-type doped layer. Mesa structures with the area
A 1.410–2 cm2 and the depth of p-n junction close to
3 m were prepared.
The mirror-like surface of the substrate was
observed after Cd diffusion, but the surface roughness
slightly increased from ~0.03 in the initial substrate up
to ~0.05 µm. The average concentration of holes in the
doped surface layer (7 1)1018 cm–3 at the temperature
77 K was estimated from differential Hall effect
measurements [15]. Ohmic contacts were made using
thermal vacuum deposition of In-Zn alloy and In on p-
and n-type region of the substrate, respectively.
Passivation and protection of mesa structures was made
using deposition of thin (0.5…0.6 µm) CdTe films. This
passivation results in the surface states density
(0.5…1.0)1011 eV–1cm–2 at the InSb/CdTe interface,
which is 2 to 3 times lower than in the case of anodic
oxidation of InSb [16, 17]. The current-voltage
characteristics and high-frequency (f = 1 MHz) barrier
capacitance were measured for characterization of
photodiodes.
3. Results and discussion
Typical current-voltage characteristics measured at the
temperature 77 K is shown in Fig. 1. At the bias voltage
U = ±250 mV, the rectification coefficient was 6·103. As
seen from Fig. 1, the reverse current smoothly increases
with the bias increase. The breakdown voltage was in the
range 0.7…0.8 V, whereas the diffusion potential was
eUD ≈ 160 meV. The measured capacitance-voltage
characteristics were better linearized in coordinates
C–3 – U (Fig. 2), indicating formation of a linearly-
graded p-n junction. The dopant concentration gradient
a 1.01019 cm–4 as well as the diffusion voltage close to
190 mV were determined from the capacitance
measurements. The depletion layer thickness at zero bias
W0 ≈ 1.2 m was estimated. Experimental data are
summarized in Table.
-800 -400 0 400
-0.1
0.1
-0.2
0.4
0.2
0.3
0
I,
m
A
U, mV
Fig. 1. Current-voltage characteristics of diffusion InSb p-n
junctions at 77 K.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 325-330.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
327
-200 -150 -100 -50 0 50 100
0
2
4
6
8
10
U, mV
C
-2
, 1
019
, F
-2
0
1
2
3
4
5
6
7
8
C
-3
, 1
029
, F
-3
Fig. 2. High-frequency (1 MHz) capacitance-voltage
characteristics of diffusion InSb p-n junctions at 77 K plotted
in different coordinates.
The current-voltage characteristics measured at
different temperatures are shown in Fig. 3. Note some
peculiarities in the behavior of forward I–U
characteristics. At T = 77 K, two exponential parts are
observed, which can be described by the following
equation:
kT
IRUe
I
E
IRUe
II SS expexp 02
0
01 , (1)
where I01, I02 are the pre-exponential factors; E0 ≈
29 meV is the characteristic energy; β ≈ 1.6 is the
ideality coefficient; RS ≈1.5 Ohm is the series resistance.
At higher temperatures only one exponential part
(curve 2) is observed. Deviation from the exponential
dependence at bias voltages U > UD is explained by the
series resistance effect. Moreover, due to this effect with
further increase in temperature (T > 116 K), the
exponential part is not observed at all (curve 3). The
UI dependence corrected to the series resistance is
shown in Fig. 3 (curve 4).
Note that the diode effect is not observed at bias
voltages |U| ≤ 10 mV on the forward and reverse current-
voltage characteristics, which is caused by the surface
leakage current. At the same time, rather low values of
shunt voltages indicate effectiveness of passivation by
using CdTe films. Because of investigated junctions are
characterized by large ratio of the junction area to the
perimeter length, the contribution of the surface leakage
at higher biases seems to be low.
0 50 100 150 200
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
1'
2'
3'
4 3
2
1
I,
A
U, mV
Fig. 3. Forward (closed dots) and reverse (open dots) I–U
curves at temperatures, K: 77 (1, 1), 116 (2, 2), 156 (3, 3).
The curve 4 is corrected to the series resistance effect.
Results of experimental data processing are shown
in Table. The intrinsic concentration was calculated
using the formulas given in [18, 19], where Nc (cm–3) =
8.0·1012T3/2, Nv (cm–3) = 1.4·1015T3/2 are the effective
density of states in the conduction and valence band,
respectively. The temperature dependence of the band
gap Eg has been approximated by the formula
Eg (eV) = 500/100.624.0 24 TT .
To understand the behavior of reverse UI
characteristics, experimental results are shown in double
logarithmic coordinates (Fig. 4). As seen, they are
satisfactorily approximated by a power law I ~ Un,
where the exponent n is varied with temperature. At T =
77 K (curve 1) in the voltage range 23 1001 U , the
linear dependence is observed with n ≈ 1.0 followed by
the sub-linear one with n ≈ 0.8 at the bias voltages
2.0012 2 U . Finally, at U > 0.3 V the current
tends to a sharp increase that may be due to the
breakdown state of a junction. Similar behavior of the
reverse current is also observed at T = 116 K (curve 2).
With temperature increasing (curve 3), the sub-linear
curve with n = 0.3 is observed at U > 0.07 V, which is
typical for the generation current in a linearly-graded p-n
junction [20]. Such behavior of the reverse current is
explained by predominant contribution of tunneling
current within the temperature range 77…116 K, while
at T = 156 K it is mainly determined by the generation
carrier component.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 325-330.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
328
1 10 100
10-7
10-6
10-5
10-4
10-3
3
2
1I,
A
U, mV
Fig. 4. Reverse current-voltage charateristics at temperatures,
K: 77 (1), 116 (2), 156 (3).
The temperature dependence of the resistance-area
product R0A at the forward bias voltage of 5 mV is
shown in Fig. 5. As seen, it increases with temperature
decreasing at temperatures from 160 to 120 K with the
activation energy ΔE = 0.14 eV. With further decrease of
temperature (T < 120 K) a tendency to saturation is seen.
Thus, the temperature dependence of R0A is explained by
dominant contribution of generation and tunnel currents
at high and low temperatures, respectively. This
conclusion is based on the value of the activation energy,
which is typical for the generation current in the
depletion region, as well as on the value of the ideality
coefficient at T <120 K (see Figs 3 and 4). Note that in
the absence of tunneling current at the temperature 77 K
the product R0A could be close to 3.5·104 Ohm·cm2. This
value is almost one order of magnitude higher than that
in commercially available InSb photodiodes [21].
Thus, based on experimental results described
above, one can conclude that the investigated junctions
are linearly-graded. The excess current observed in these
junctions has tunneling nature. Since the thickness of the
depletion layer W0 decreases from 1.2 m at 77 K to
1.0 m at 134 K (see Table), the interband tunneling
cannot be dominant at rather low bias voltages |U| ≤ ±UD .
Therefore, it is most likely that tunneling occurs through
deep defect states localized in the depletion layer [22-25].
Several models of tunneling current in infrared
photodiodes were proposed in the literature [1, 20, 22,
23]. For instance, in the reverse-biased HgCdTe
photodiodes, the soft breakdown was explained by the
trap-assisted tunneling mechanism [22, 23]. However, as
in the case of InAs p-n junctions [25], investigated InSb
junctions were found to be substantially influenced by
ultrasonic treatment. So, to explain experimental results at
forward and reverse biases, the model of tunneling current
through dislocations was chosen [24]. According to this
model, the forward tunneling current is approximated by
an equation similar to the first component in Eq. (1), and
the temperature dependence of the pre-exponential factor
is given by the formula I0 ~ exp (bT), where 0/ Eb
and E0 is the characteristic energy.
Figs 6a and 6b show temperature dependences of
the dark current in the investigated junction. As seen, in
TI /10lg 3 coordinates the current exhibits similar
behavior for reverse and forward bias voltages. The
activation energy ΔE 0.14 eV was found from the
slope of the linear parts at temperatures T > 116 K.
Approximation of experimental data by the formula
I ~ exp(bT) results in the average value of
12 K019.2 b .
The diffusion potential and energy gap as a function
of temperature are shown in Fig. 7. The value of eUD =
250 meV determined from the extrapolation to zero
temperature is close to the energy gap of InSb [18, 19].
From the slope of eUD vs. T dependence values of
coefficients 1.210–3 eV/K and b = / E0 4.110–2 K–1
were found. As seen, the value of b is close to that found
from the temperature dependence of current. At
temperatures T ≥ 70 K, the energy gap is approximated
by the linear function Eg(T) = 0 – T, where
a 2.010–4 eV/K for the temperature range 77 to 160 K
and Δ0 ≈ 250 meV is close to Eg (0 K) ≈ 240 meV. The
linear approximation is necessary to estimate γ [24]:
np
NN
k vcln . (2)
6 8 10 12 14
0.1
1
10
103/T, K-1
R
0A
,
c
m
2
Fig. 5. Temperature dependence of R0A at the bias voltage
5 mV.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 325-330.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
329
6 7 8 9 10 11 12 13 14
10-6
10-5
10-4
10-3
10-2
a
2
1
I,
A
103/T, K-1
a)
80 100 120 140
10-6
10-5
10-4
10-3
b
2
1
I,
A
T, K b)
Fig. 6. (a, b) Temperature dependence of the dark current
at 5 mV (1) and –50 mV (2) plotted in different coordinates.
To estimate the coefficient , the concentration of
carriers at the edge of the depletion region can be
calculated using the formula n = p = aW0/2 ≈
314 cm010.6 for values of W0 given in Table. The
calculated and experimental data (1.110–3 and
eV/K012.1 3 , respectively) are in good agreement.
The model developed in [24] allows us to estimate the
dislocation density in the depletion layer
0
0 exp
E
eU
AeI D , (3)
where I0 is the pre-exponential factor; ρ – density of
dislocations; ν – Debye frequency. At the temperature
77 K, experimental parameters are as follows: I0/A =
9.310–5 A/cm2, eUD = 160 meV, E0 = 29 meV and
112s013.3 . The frequency ν is estimated using the
Debye temperature TD ≈ 160 K for InSb [18, 19]. The
calculated dislocation density 4.4104 cm–2 is two
orders of magnitude higher than that in the starting
substrates. Rather high density of dislocations may be
caused by relaxation of mechanical stresses that arise
during dopant Cd diffusion into substrates.
In the investigated junctions, tunneling and
generation-recombination current flows through
different parts of p-n junction, namely: through the
junction parts enriched with dislocations and those parts
that are free of dislocations, respectively. At low bias
voltages U ≥ 3kT/e, the tunneling current is approxi-
mated by the first term of Eq. (1), whereas the
generation current is approximated by the second term at
higher bias voltages. At temperatures T ≥ 116 K, the
generation current is dominant over the whole range of
bias voltages (Fig. 3, curve 2). Tunneling of carriers in
the model [24] occurs in the form of successive jumps
along the dislocation line initiated by phonons. This
model has been successively used for explanation of
experimental data in GaP diode structures that were
characterized by a high dislocation density [24].
However, it seems that the dislocation density in the
investigated InSb junctions is overestimated. Also, this
model does not consider impurity centers, forming
Cottrell atmosphere. The tunneling mechanism that
includes participation of Cottrell atmospheres has been
considered in application to InAs photodiodes in [25].
Obviously, discrimination of carrier transport mecha-
nisms in the linearly-graded InSb p-n junctions requires
additional study, but participation of dislocations in the
carrier transport seems to be doubtless.
0 50 100 150
50
100
150
200
250
2
1
eU
D
, E
g,
m
eV
T, K
Fig. 7. Temperature dependence of diffusion potential eUD (1)
and band gap Eg (2).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 325-330.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
330
4. Conclusions
1. The excess current is investigated in InSb p-n-
junctions prepared by diffusion of Cd into mono-
crystalline substrates of n-type conductivity. The
linear distribution of dopant atoms has been found
from the capacitance-voltage measurements. The
mesa structure junctions were passivated by CdTe
films.
2. Experimental results have been explained using the
model of inhomogeneous p-n junction. It is shown
that tunneling of carriers occurs through the states
in the gap related to dislocations in the depletion
region. The generation-recombination current flows
through the depletion region free of dislocations.
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photodiodes // Prikladnaia Fizika, 1, p. 56-62
(2002), in Russian.
10. V.A. Bogatyrev, A.A. Gavrilov, G.A. Kochurin
et al., Electrical and photoelectric properties of p-n
transitions on InSb prepared by introduction of zinc
ions with subsequent diffusion distillation // Sov.
Phys. Semicond. 12(11), p. 2106-2109 (1978).
11. B.S. Kerner, V.V. Osipov, O.V. Smolin et al., On
the mechanism of excess currents in p-n junctions //
Sov. Phys. Semicond. 20(9), p. 1739-1742 (1986).
12. V.P. Astahov, V.F. Dudkin, B.S. Kerner et al.,
Mechanisms of burst noise p-n junctions //
Microelectronics, 18(5), p. 455-463 (1989), in
Russian.
13. A.V. Sukach, V.V. Tetyorkin, N.M. Krolevec,
Tunneling current via dislocations in InAs and InSb
infrared photodiodes // Semiconductor Physics,
Quantum Electronics and Optoelectronics, 14(4),
p. 416-420 (2011).
14. I.F. Dawald, The kinetics and mechanism of
formation of anode films on single crystal InSb // J.
Electrochem. Soc. 104(4), p. 244-251 (1957).
15. D.K. Schroder, Semiconductor Material and
Device Characterization. Wiley, 2006.
16. I.V. Varlamov, L.A. Vjukov, O.V. Kulikova et al.,
Photomemory effect in InSb-CdTe heterojunctions
// Sov. Phys. Semicond. 15(12), p. 2423-2426
(1981).
17. Y.A. Bykovskii, L.A. Packs, A.G. Dudoladov
et al., Investigation of MIS film structures based on
CdTe-InSb // Pisma Zhurnal Techn. Fiziki, 9(7),
p. 1071-1074 (1983), in Russian.
18. O. Madelung, Semiconductor. Basis Data.
Springer, Berlin, 1996.
19. htpp://www.ioffe.ru/SVA/NSM/semicond/.
20. S.M. Sze, Physics of Semiconductor Devices.
Wiley, N.Y., 1981.
21. Indium Antimonide Detectors. Catalog. Judson
Technologies LLC, 2012.
22. D. Rosenfeld and G. Bahir, A model for the trap
assisted tunneling mechanism in diffused n-p and
implanted n+-p HgCdTe photodiodes // IEEE
Trans. Electron. Devices, 39(7), p. 1638-1645
(1992).
23. Y. Nemirovsky and A. Unicovsky, Tunneling and
1/f noise currents in HgCdTe photodiodes // J. Vac.
Sci. Technol. B, 10(4), p. 1602-1610 (1992).
24. V.V. Evstropov, M. Dzhumaeva, Yu.V. Zhilaev
et al., Dislocation origin and a model of the
excessive tunnel current in GaP p-n structures //
Semiconductors, 34(11), p. 1357-1362 (2000).
25. V. Tetyorkin, A. Sukach, A. Tkachuk, InAs
Infrared Photodiodes, In: Advances in Photodiodes,
Ed. Gian-Franco Dalla Betta, InTech, 2011.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 325-330.
PACS 73.40.Kp, 73.40.Gk
Carrier transport mechanisms in InSb diffusion p-n junctions
A. Sukach1, V. Tetyorkin1, A. Voroschenko1, A. Tkachuk2, M. Kravetskii1, I. Lucyshyn1
1V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine,
41, prospect Nauky, 03028 Kyiv, Ukraine
2V. Vinnichenko Kirovograd State Pedagogical University, Kirovograd, Ukraine
Phone: 38 (044) 525-54-61, e-mail: teterkin@isp.kiev.ua
Abstract. The linearly-graded p-n junctions were prepared by diffusion of cadmium into n-InSb(100) substrate with the electron concentration n ( 1.6(1015 cm–3 at the temperature T = 77 K. Passivation and protection of mesa structures have been carried out using thin films of CdTe. Forward and reverse current-voltage characteristics were investigated within the temperature range 77…156 K. It has been found that the total dark current consists of generation-recombination and tunneling current components, which are dominant at high (T = 120…156 K) and low (T < 120 K) temperatures, respectively. Experimental results have been explained using the model of a nonhomogeneous p-n junction. It has been shown that in the linearly-graded p-n junction with the rather thick (~1 (m) depletion region tunneling current flows through the states related to dislocations in the depletion region. The performed estimation of electrical parameters of diffusion InSb p-n junctions allows to predict behavior of InSb-based photodiodes at operation temperatures T > 77 K.
Keywords: infrared, InSb, linearly-graded junctions, dislocations, tunneling.
Manuscript received 19.01.14; revised version received 11.06.14; accepted for publication 29.10.14; published online 10.11.14.
1. Introduction
InSb photodiodes are widely used for detection of infrared radiation within the spectral range 3 to 5 (m. High structural perfection (low density of dislocations and low-angle boundaries), uniformity and stability of bulk InSb allow production of focal-plane arrays and matrices [1-3]. Development of 2052×2052 InSb photodiode matrix has been reported in [4]. The photodiodes are usually produced by ion implantation of beryllium, magnesium [5] or thermal diffusion of zinc [2] and cadmium into n-InSb bulk substrates [1, 3, 4, 7].
Despite the fact that the development of high-quality InSb photodiodes is known for a long time [5], the problem of improving basic technical parameters and characteristics remains valid until now [7-9]. Especially important is to understand reasons of frequently observed excess dark currents in the photodiodes, which lead to worsening their performances. Availability of excess current in a photodiode means that the measured current can not be explained by bulk diffusion and the generation-recombination carrier transport mechanism. For instance, the excess current associated with the surface leakage was observed at temperatures 77…110 K in the reverse-biased planar InSb p+-n junctions [2]. Similarly, this current was detected in mesa junctions at forward biases [10]. The excess current in InSb photodiodes is ascribed to tunneling [11, 12], trap-assisted tunneling [7] and dislocations [13]. Note that in the cited works, except [2], studies were performed at the fixed temperature 77 K. The purpose of this paper is to study carrier transport mechanisms in a wide temperature range. It is clear from the above consideration is important from both scientific and practical point of view.
2. Samples and experimental techniques
InSb p-n junctions were produced by diffusion of cadmium into n-InSb monocrystalline substrates with the (100) crystallographic orientation. The electron concentration and mobility at T = 77 K were 1.6(1015 cm–3 and 6.4·105 cm2/V·s, respectively. The surface damaged layer in substrates was removed by chemical dynamic polishing using a polishing etchant 2% Br2 – 98% HBr. The quality of the polished surface was controlled by an interference microscope and by measuring its roughness. The average dislocation density determined by selective etching was ~300 cm–2 [14]. Diffusion of Cd was carried out for 30 min using the two-temperature method. The substrate and source temperatures were ~400 and 380 ºC, respectively. To prevent re-evaporation of components from the substrate, an additional powder of Sb and In was loaded into ampoule to ensure conditions of vapor saturation. The thickness of the substrate was close to 500 (m. The depth of p-n junction was determined by measuring the sign of thermo-emf during the layer-by-layer etching of p-type doped layer. Mesa structures with the area A ( 1.4(10–2 cm2 and the depth of p-n junction close to 3 (m were prepared.
The mirror-like surface of the substrate was observed after Cd diffusion, but the surface roughness slightly increased from ~0.03 in the initial substrate up to ~0.05 µm. The average concentration of holes in the doped surface layer (7 ( 1)(1018 cm–3 at the temperature 77 K was estimated from differential Hall effect measurements [15]. Ohmic contacts were made using thermal vacuum deposition of In-Zn alloy and In on p- and n-type region of the substrate, respectively. Passivation and protection of mesa structures was made using deposition of thin (0.5…0.6 µm) CdTe films. This passivation results in the surface states density (0.5…1.0)(1011 eV–1cm–2 at the InSb/CdTe interface, which is 2 to 3 times lower than in the case of anodic oxidation of InSb [16, 17]. The current-voltage characteristics and high-frequency (f = 1 MHz) barrier capacitance were measured for characterization of photodiodes.
3. Results and discussion
Typical current-voltage characteristics measured at the temperature 77 K is shown in Fig. 1. At the bias voltage U = ±250 mV, the rectification coefficient was 6·103. As seen from Fig. 1, the reverse current smoothly increases with the bias increase. The breakdown voltage was in the range 0.7…0.8 V, whereas the diffusion potential was eUD ≈ 160 meV. The measured capacitance-voltage characteristics were better linearized in coordinates
C–3 – U (Fig. 2), indicating formation of a linearly-graded p-n junction. The dopant concentration gradient a ( 1.0(1019 cm–4 as well as the diffusion voltage close to 190 mV were determined from the capacitance measurements. The depletion layer thickness at zero bias W0 ≈ 1.2 (m was estimated. Experimental data are summarized in Table.
-800-4000400
-0.1
0.1
-0.2
0.4
0.2
0.3
0
I, mA
U, mV
Fig. 1. Current-voltage characteristics of diffusion InSb p-n junctions at 77 K.
-200-150-100-50050100
0
2
4
6
8
10
U, mV
C
-2
, 10
19
, F
-2
0
1
2
3
4
5
6
7
8
C
-3
, 10
29
, F
-3
Fig. 2. High-frequency (1 MHz) capacitance-voltage characteristics of diffusion InSb p-n junctions at 77 K plotted in different coordinates.
The current-voltage characteristics measured at different temperatures are shown in Fig. 3. Note some peculiarities in the behavior of forward I–U characteristics. At T = 77 K, two exponential parts are observed, which can be described by the following equation:
(
)
(
)
ú
û
ù
ê
ë
é
b
-
+
ú
û
ù
ê
ë
é
-
=
kT
IR
U
e
I
E
IR
U
e
I
I
S
S
exp
exp
02
0
01
,
(1)
where I01, I02 are the pre-exponential factors; E0 ≈ 29 meV is the characteristic energy; β ≈ 1.6 is the ideality coefficient; RS ≈1.5 Ohm is the series resistance. At higher temperatures only one exponential part (curve 2) is observed. Deviation from the exponential dependence at bias voltages U > UD is explained by the series resistance effect. Moreover, due to this effect with further increase in temperature (T > 116 K), the exponential part is not observed at all (curve 3). The
U
I
-
dependence corrected to the series resistance is shown in Fig. 3 (curve 4).
Note that the diode effect is not observed at bias voltages |U| ≤ 10 mV on the forward and reverse current-voltage characteristics, which is caused by the surface leakage current. At the same time, rather low values of shunt voltages indicate effectiveness of passivation by using CdTe films. Because of investigated junctions are characterized by large ratio of the junction area to the perimeter length, the contribution of the surface leakage at higher biases seems to be low.
050100150200
10
-8
10
-7
10
-6
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
1
'
2
'
3
'
4
3
2
1
I, A
U, mV
Fig. 3. Forward (closed dots) and reverse (open dots) I–U curves at temperatures, K: 77 (1, 1(), 116 (2, 2(), 156 (3, 3(). The curve 4 is corrected to the series resistance effect.
Results of experimental data processing are shown in Table. The intrinsic concentration was calculated using the formulas given in [18, 19], where Nc (cm–3) = 8.0·1012T3/2, Nv (cm–3) = 1.4·1015T3/2 are the effective density of states in the conduction and valence band, respectively. The temperature dependence of the band gap Eg has been approximated by the formula
Eg (eV) =
(
)
500
/
10
0
.
6
24
.
0
2
4
+
×
-
-
T
T
.
To understand the behavior of reverse
U
I
-
characteristics, experimental results are shown in double logarithmic coordinates (Fig. 4). As seen, they are satisfactorily approximated by a power law I ~ Un, where the exponent n is varied with temperature. At T = 77 K (curve 1) in the voltage range
2
3
10
0
1
-
-
£
<
U
, the linear dependence is observed with n ≈ 1.0 followed by the sub-linear one with n ≈ 0.8 at the bias voltages
2
.
0
0
1
2
2
£
<
×
-
U
. Finally, at U > 0.3 V the current tends to a sharp increase that may be due to the breakdown state of a junction. Similar behavior of the reverse current is also observed at T = 116 K (curve 2). With temperature increasing (curve 3), the sub-linear curve with n = 0.3 is observed at U > 0.07 V, which is typical for the generation current in a linearly-graded p-n junction [20]. Such behavior of the reverse current is explained by predominant contribution of tunneling current within the temperature range 77…116 K, while at T = 156 K it is mainly determined by the generation carrier component.
110100
10
-7
10
-6
10
-5
10
-4
10
-3
3
2
1
I, A
U, mV
Fig. 4. Reverse current-voltage charateristics at temperatures, K: 77 (1), 116 (2), 156 (3).
The temperature dependence of the resistance-area product R0A at the forward bias voltage of 5 mV is shown in Fig. 5. As seen, it increases with temperature decreasing at temperatures from 160 to 120 K with the activation energy ΔE = 0.14 eV. With further decrease of temperature (T < 120 K) a tendency to saturation is seen. Thus, the temperature dependence of R0A is explained by dominant contribution of generation and tunnel currents at high and low temperatures, respectively. This conclusion is based on the value of the activation energy, which is typical for the generation current in the depletion region, as well as on the value of the ideality coefficient at T <120 K (see Figs 3 and 4). Note that in the absence of tunneling current at the temperature 77 K the product R0A could be close to 3.5·104 Ohm·cm2. This value is almost one order of magnitude higher than that in commercially available InSb photodiodes [21].
Thus, based on experimental results described above, one can conclude that the investigated junctions are linearly-graded. The excess current observed in these junctions has tunneling nature. Since the thickness of the depletion layer W0 decreases from 1.2 (m at 77 K to 1.0 (m at 134 K (see Table), the interband tunneling cannot be dominant at rather low bias voltages |U| ≤ ±UD . Therefore, it is most likely that tunneling occurs through deep defect states localized in the depletion layer [22-25]. Several models of tunneling current in infrared photodiodes were proposed in the literature [1, 20, 22, 23]. For instance, in the reverse-biased HgCdTe photodiodes, the soft breakdown was explained by the trap-assisted tunneling mechanism [22, 23]. However, as in the case of InAs p-n junctions [25], investigated InSb junctions were found to be substantially influenced by ultrasonic treatment. So, to explain experimental results at forward and reverse biases, the model of tunneling current through dislocations was chosen [24]. According to this model, the forward tunneling current is approximated by an equation similar to the first component in Eq. (1), and the temperature dependence of the pre-exponential factor is given by the formula I0 ~ exp (bT), where
0
/
E
b
g
=
and E0 is the characteristic energy.
Figs 6a and 6b show temperature dependences of the dark current in the investigated junction. As seen, in
T
I
/
10
lg
3
-
coordinates the current exhibits similar behavior for reverse and forward bias voltages. The activation energy ΔE ( 0.14 eV was found from the slope of the linear parts at temperatures T > 116 K. Approximation of experimental data by the formula I ~ exp(bT) results in the average value of
1
2
K
0
1
9
.
2
-
-
×
»
b
.
The diffusion potential and energy gap as a function of temperature are shown in Fig. 7. The value of eUD = 250 meV determined from the extrapolation to zero temperature is close to the energy gap of InSb [18, 19]. From the slope of eUD vs. T dependence values of coefficients ( ( 1.2(10–3 eV/K and b = ( / E0 ( 4.1(10–2 K–1 were found. As seen, the value of b is close to that found from the temperature dependence of current. At temperatures T ≥ 70 K, the energy gap is approximated
by the linear function Eg(T) = (0 – (T, where
a ( 2.0(10–4 eV/K for the temperature range 77 to 160 K and Δ0 ≈ 250 meV is close to Eg (0 K) ≈ 240 meV. The linear approximation is necessary to estimate γ [24]:
÷
÷
ø
ö
ç
ç
è
æ
+
a
»
g
np
N
N
k
v
c
ln
.
(2)
68101214
0.1
1
10
10
3
/T, K
-1
R
0
A,
cm
2
Fig. 5. Temperature dependence of R0A at the bias voltage 5 mV.
67891011121314
10
-6
10
-5
10
-4
10
-3
10
-2
a
2
1
I, A
10
3
/T, K
-1
a)
80100120140
10
-6
10
-5
10
-4
10
-3
b
2
1
I, A
T, K
b)
Fig. 6. (a, b) Temperature dependence of the dark current at 5 mV (1) and –50 mV (2) plotted in different coordinates.
To estimate the coefficient (, the concentration of carriers at the edge of the depletion region can be calculated using the formula n = p = aW0/2 ≈
3
14
cm
0
1
0
.
6
-
×
»
for values of W0 given in Table. The calculated and experimental data (1.1(10–3 and
eV/K
0
1
2
.
1
3
-
×
, respectively) are in good agreement. The model developed in [24] allows us to estimate the dislocation density in the depletion layer
÷
÷
ø
ö
ç
ç
è
æ
-
n
r
=
0
0
exp
E
eU
A
e
I
D
,
(3)
where I0 is the pre-exponential factor; ρ – density of dislocations; ν – Debye frequency. At the temperature 77 K, experimental parameters are as follows: I0/A = 9.3(10–5 A/cm2, eUD = 160 meV, E0 = 29 meV and
1
12
s
0
1
3
.
3
-
×
»
n
. The frequency ν is estimated using the Debye temperature TD ≈ 160 K for InSb [18, 19]. The calculated dislocation density ( ( 4.4(104 cm–2 is two orders of magnitude higher than that in the starting substrates. Rather high density of dislocations may be caused by relaxation of mechanical stresses that arise during dopant Cd diffusion into substrates.
In the investigated junctions, tunneling and generation-recombination current flows through different parts of p-n junction, namely: through the junction parts enriched with dislocations and those parts that are free of dislocations, respectively. At low bias voltages U ≥ 3kT/e, the tunneling current is approxi-mated by the first term of Eq. (1), whereas the generation current is approximated by the second term at higher bias voltages. At temperatures T ≥ 116 K, the generation current is dominant over the whole range of bias voltages (Fig. 3, curve 2). Tunneling of carriers in the model [24] occurs in the form of successive jumps along the dislocation line initiated by phonons. This model has been successively used for explanation of experimental data in GaP diode structures that were characterized by a high dislocation density [24]. However, it seems that the dislocation density in the investigated InSb junctions is overestimated. Also, this model does not consider impurity centers, forming Cottrell atmosphere. The tunneling mechanism that includes participation of Cottrell atmospheres has been considered in application to InAs photodiodes in [25]. Obviously, discrimination of carrier transport mecha-nisms in the linearly-graded InSb p-n junctions requires additional study, but participation of dislocations in the carrier transport seems to be doubtless.
050100150
50
100
150
200
250
2
1
eU
D
, E
g
, meV
T, K
Fig. 7. Temperature dependence of diffusion potential eUD (1) and band gap Eg (2).
4. Conclusions
1. The excess current is investigated in InSb p-n-junctions prepared by diffusion of Cd into mono- crystalline substrates of n-type conductivity. The linear distribution of dopant atoms has been found from the capacitance-voltage measurements. The mesa structure junctions were passivated by CdTe films.
2.
Experimental results have been explained using the model of inhomogeneous p-n junction. It is shown that tunneling of carriers occurs through the states in the gap related to dislocations in the depletion region. The generation-recombination current flows through the depletion region free of dislocations.
References
1. A. Rogalski, Infrared Photon Detectors. SPIE Optical Eng. Press, N.Y., 1995.
2. P.V. Biryulin, V.I. Turin, E.B. Yakimov, Investigation of characteristics of photodiode arrays based on InSb // Semiconductors, 38(4), p. 498-503 (2004).
3. A.M. Filachev, I.D. Burlakov, A.I. Dirochka et al., High-speed photodetector 128×128 cells based on InSb with frame accumulation and range finder function // Prikladnaia Fizika, 2, p. 21-25 (2005), in Russian.
4. A. Rogalski, Optical detectors for focal plane arrays // Optoelectron. Rev. 12(2), p. 221-245 (2004).
5. C.E. Hurwitz, I.P. Donnely, Planar InSb-photodiodes fabricated by Be and Mg ion implantation // Solid State Electron. 18(9), p. 753-756 (1975).
6. V.P. Astahov, D.A. Gindin, V.V. Karpov, A.V. Talimov, Results of development of InSb photodiodes with ultralow dark current for high-sensitivity IR CCD // Prikladnaia Fizika, 3, p. 68-71 (2002), in Russian.
7. M. Moradi, M. Daraee, M. Hajian et al., Optimum concentration of InSb photodiode for minimum low reverse bias leakage current // Ukr. J. Phys. 55(4), p. 422-424 (2010).
8. V.P. Astahov, D.A. Gindin, V.V. Karpov et al., On the possibility of increasing the current sensitivity of photodiodes based on InSb // Prikladnaia Fizika, 2, p. 73-79 (1999), in Russian.
9. V.P. Astakhov, D.A. Gindin, V.V. Karpov, AV. Talimov, Thermal stability increase in InSb photodiodes // Prikladnaia Fizika, 1, p. 56-62 (2002), in Russian.
10.
V.A. Bogatyrev, A.A. Gavrilov, G.A. Kochurin et al., Electrical and photoelectric properties of p-n transitions on InSb prepared by introduction of zinc ions with subsequent diffusion distillation // Sov. Phys. Semicond. 12(11), p. 2106-2109 (1978).
11. B.S. Kerner, V.V. Osipov, O.V. Smolin et al., On the mechanism of excess currents in p-n junctions // Sov. Phys. Semicond. 20(9), p. 1739-1742 (1986).
12. V.P. Astahov, V.F. Dudkin, B.S. Kerner et al., Mechanisms of burst noise p-n junctions // Microelectronics, 18(5), p. 455-463 (1989), in Russian.
13. A.V. Sukach, V.V. Tetyorkin, N.M. Krolevec, Tunneling current via dislocations in InAs and InSb infrared photodiodes // Semiconductor Physics, Quantum Electronics and Optoelectronics, 14(4), p. 416-420 (2011).
14. I.F. Dawald, The kinetics and mechanism of formation of anode films on single crystal InSb // J. Electrochem. Soc. 104(4), p. 244-251 (1957).
15. D.K. Schroder, Semiconductor Material and Device Characterization. Wiley, 2006.
16. I.V. Varlamov, L.A. Vjukov, O.V. Kulikova et al., Photomemory effect in InSb-CdTe heterojunctions // Sov. Phys. Semicond. 15(12), p. 2423-2426 (1981).
17. Y.A. Bykovskii, L.A. Packs, A.G. Dudoladov et al., Investigation of MIS film structures based on CdTe-InSb // Pisma Zhurnal Techn. Fiziki, 9(7), p. 1071-1074 (1983), in Russian.
18. O. Madelung, Semiconductor. Basis Data. Springer, Berlin, 1996.
19. htpp://www.ioffe.ru/SVA/NSM/semicond/.
20. S.M. Sze, Physics of Semiconductor Devices. Wiley, N.Y., 1981.
21. Indium Antimonide Detectors. Catalog. Judson Technologies LLC, 2012.
22. D. Rosenfeld and G. Bahir, A model for the trap assisted tunneling mechanism in diffused n-p and implanted n+-p HgCdTe photodiodes // IEEE Trans. Electron. Devices, 39(7), p. 1638-1645 (1992).
23. Y. Nemirovsky and A. Unicovsky, Tunneling and 1/f noise currents in HgCdTe photodiodes // J. Vac. Sci. Technol. B, 10(4), p. 1602-1610 (1992).
24. V.V. Evstropov, M. Dzhumaeva, Yu.V. Zhilaev et al., Dislocation origin and a model of the excessive tunnel current in GaP p-n structures // Semiconductors, 34(11), p. 1357-1362 (2000).
25. V. Tetyorkin, A. Sukach, A. Tkachuk, InAs Infrared Photodiodes, In: Advances in Photodiodes, Ed. Gian-Franco Dalla Betta, InTech, 2011.
Table. Experimental and calculated parameters of InSb diffusion p-n junctions.
T, K�
I02, A�
β�
U0, mV�
ni, cm–3�
W0, (m�
τ0, s�
RS, (�
�
77�
4·10–9�
1.6�
160�
1.6·109�
1.2�
1.1·10–7�
1.5�
�
116�
1.6·10–5�
1.6�
115�
1.6·1012�
1.1�
2.5·10–8�
1.7�
�
134�
2.6·10–4�
1.6�
90�
1.1·1013�
1.0�
9.5·10–9�
1.9�
�
156�
1.3·10–3�
1.5�
65�
6.3·1013�
0.9�
9.8·10–9�
2.1�
�
Notes: U0 – current cutoff voltage, τ0 – carrier lifetime in the depletion region
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
325
_1475591352.unknown
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_1477906349.unknown
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_1475591427.unknown
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