Optimization of technology for fabrication of sectional nuclear radiation detectors based on high-resistance silicon
On the basis of experimental studies the surface-barrier technology for fabrication of sectional nuclear radiation detectors with using of the high-resistance n-Si plates of large diameter (~ 100 mm) was optimized. The 9-sectional detector matrixes were manufactured. In such matrix each section is a...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2017
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| Цитувати: | Optimization of technology for fabrication of sectional nuclear radiation detectors based on high-resistance silicon / G.P. Gaidar, S.V. Berdnichenko, V.G. Vorobyov, V.I. Kochkin, V.F. Lastovetskiy, P.G. Litovchenko // Вопросы атомной науки и техники. — 2017. — № 2. — С. 201-208. — Бібліогр.: 25 назв. — англ. |
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irk-123456789-1360222018-06-16T03:03:33Z Optimization of technology for fabrication of sectional nuclear radiation detectors based on high-resistance silicon Gaidar, G.P. Berdnichenko, S.V. Vorobyov, V.G. Kochkin, V.I. Lastovetskiy, V.F. Litovchenko, P.G. Диагностика и методы исследований On the basis of experimental studies the surface-barrier technology for fabrication of sectional nuclear radiation detectors with using of the high-resistance n-Si plates of large diameter (~ 100 mm) was optimized. The 9-sectional detector matrixes were manufactured. In such matrix each section is a separate detector with the thickness of sensitive area W ≤ 350 μm, the working area S = 4 cm², and the energy resolution R = 50…75 keV under irradiation by three-component α-source. The electrophysical and spectrometric characteristics of the sectional silicon detectors were determined. The manufactured detectors can be used in the nuclear experiments involving heavy ions at the low yields of reaction products. На основі проведених експериментальних досліджень оптимізовано поверхнево-бар'єрну технологію виготовлення секційних детекторів ядерних випромінювань з використанням пластин високоомного n-Si великого діаметра (~ 100 мм). Виготовлено 9-секційні детекторні матриці, де кожна секція є окремим детектором з товщиною чутливої області W ≤ 350 мкм, робочою площею S = 4 см² та енергетичною роздільною здатністю R = 50…75 кеВ при опроміненні трикомпонентним α-джерелом. Визначено електрофізичні та спектрометричні характеристики секційних кремнієвих детекторів. Виготовлені детектори можуть бути використані в ядерних експериментах за участю важких іонів при низьких виходах продуктів реакцій. На основе проведенных экспериментальных исследований оптимизирована поверхностно-барьерная технология изготовления секционных детекторов ядерных излучений с использованием пластин высокоомного n-Si большого диаметра (~ 100 мм). Изготовлены 9-секционные детекторные матрицы, где каждая секция является отдельным детектором с толщиной чувствительной области W ≤ 350 мкм, рабочей площадью S = 4 см² и энергетическим разрешением R = 50…75 кэВ при облучении трехкомпонентным α-источником. Определены электрофизические и спектрометрические характеристики секционных кремниевых детекторов. Изготовленные детекторы могут быть использованы в ядерных экспериментах с участием тяжелых ионов при низких выходах продуктов реакций. 2017 Article Optimization of technology for fabrication of sectional nuclear radiation detectors based on high-resistance silicon / G.P. Gaidar, S.V. Berdnichenko, V.G. Vorobyov, V.I. Kochkin, V.F. Lastovetskiy, P.G. Litovchenko // Вопросы атомной науки и техники. — 2017. — № 2. — С. 201-208. — Бібліогр.: 25 назв. — англ. 1562-6016 PACS: 29.00.00; 29.40.Wk http://dspace.nbuv.gov.ua/handle/123456789/136022 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Диагностика и методы исследований Диагностика и методы исследований |
| spellingShingle |
Диагностика и методы исследований Диагностика и методы исследований Gaidar, G.P. Berdnichenko, S.V. Vorobyov, V.G. Kochkin, V.I. Lastovetskiy, V.F. Litovchenko, P.G. Optimization of technology for fabrication of sectional nuclear radiation detectors based on high-resistance silicon Вопросы атомной науки и техники |
| description |
On the basis of experimental studies the surface-barrier technology for fabrication of sectional nuclear radiation detectors with using of the high-resistance n-Si plates of large diameter (~ 100 mm) was optimized. The 9-sectional detector matrixes were manufactured. In such matrix each section is a separate detector with the thickness of sensitive area W ≤ 350 μm, the working area S = 4 cm², and the energy resolution R = 50…75 keV under irradiation by three-component α-source. The electrophysical and spectrometric characteristics of the sectional silicon detectors were determined. The manufactured detectors can be used in the nuclear experiments involving heavy ions at the low yields of reaction products. |
| format |
Article |
| author |
Gaidar, G.P. Berdnichenko, S.V. Vorobyov, V.G. Kochkin, V.I. Lastovetskiy, V.F. Litovchenko, P.G. |
| author_facet |
Gaidar, G.P. Berdnichenko, S.V. Vorobyov, V.G. Kochkin, V.I. Lastovetskiy, V.F. Litovchenko, P.G. |
| author_sort |
Gaidar, G.P. |
| title |
Optimization of technology for fabrication of sectional nuclear radiation detectors based on high-resistance silicon |
| title_short |
Optimization of technology for fabrication of sectional nuclear radiation detectors based on high-resistance silicon |
| title_full |
Optimization of technology for fabrication of sectional nuclear radiation detectors based on high-resistance silicon |
| title_fullStr |
Optimization of technology for fabrication of sectional nuclear radiation detectors based on high-resistance silicon |
| title_full_unstemmed |
Optimization of technology for fabrication of sectional nuclear radiation detectors based on high-resistance silicon |
| title_sort |
optimization of technology for fabrication of sectional nuclear radiation detectors based on high-resistance silicon |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2017 |
| topic_facet |
Диагностика и методы исследований |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/136022 |
| citation_txt |
Optimization of technology for fabrication of sectional nuclear radiation detectors based on high-resistance silicon / G.P. Gaidar, S.V. Berdnichenko, V.G. Vorobyov, V.I. Kochkin, V.F. Lastovetskiy, P.G. Litovchenko // Вопросы атомной науки и техники. — 2017. — № 2. — С. 201-208. — Бібліогр.: 25 назв. — англ. |
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Вопросы атомной науки и техники |
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ISSN 1562-6016. PAS 7 2(108), p. 201-208.
OPTIMIZATION OF TECHNOLOGY FOR FABRICATION
OF SECTIONAL NUCLEAR RADIATION DETECTORS BASED
ON HIGH-RESISTANCE SILICON
G.P. Gaidar, S.V. Berdnichenko, V.G. Vorobyov, V.I. Kochkin, V.F. Lastovetskiy,
P.G. Litovchenko
Institute for Nuclear Research of National Academy of Sciences of Ukraine, Kiev, Ukraine
E-mail: gaydar@kinr.kiev.ua
On the basis of experimental studies the surface-barrier technology for fabrication of sectional nuclear radiation
detectors with using of the high-resistance n-Si plates of large diameter ( 100 mm) was optimized. The 9-sectional
detector matrixes were manufactured. In such matrix each section is a separate detector with the thickness of
sensitive area W 350 m, the working area S = 4 cm2, and the energy resolution R = 50 75 keV under irradiation
by three-component -source. The electrophysical and spectrometric characteristics of the sectional silicon detectors
were determined. The manufactured detectors can be used in the nuclear experiments involving heavy ions at the
low yields of reaction products.
PACS: 29.00.00; 29.40.Wk
.
INTRODUCTION
In the experiments concerning investigation of the
nuclear structure and the nuclear reaction mechanisms
are almost always necessary not only to measure the
energy of particles, but also to identify them. The
numbers of reaction channels, which are opened, and
respectively the set of nuclei that are formed, are
increased with growth of the energy and mass of
bombarding particles. The nuclear radiation detectors
were used for reliable identification of the reaction
products. At present there are a large variety of
detectors depending on the type of particles, energy
range, destination, structure, and operation principle.
Semiconductor detectors are widely used in many
important experiments: for -spectroscopy [1], - and
X-ray spectroscopy [2, 3], for registration of
monoenergetic electrons [4, 5], heavy ions [6], and for
study of nuclear fission [7, 8]. Thus, the process of
nuclear fission is of great practical importance, but most
of its features are still not found an explanation. This
applies, for example, to the mechanism of asymmetric
fission [9].
With the exception of the radiochemical methods,
the devices such as dual ionization chambers or system
of flight time with the scintillation detectors were used
for study of the fission fragments. It is impossible to use
only the scintillation detector, because poor energy
resolution and saturation effect that takes place at very
high density of ionization from the fission fragments,
are inherent in it. The methods of flight time are
characterized by the high energy resolution at the small
solid angle. Semiconductor detectors allow obtaining a
very high energy resolution at the large solid angle
[10, 11]. They can be successfully used to study the
processes of fission, since the used sources and targets
must be very thin. When using semiconductor detectors,
the problem of placement of the thin active source
between two ionization chambers was removed, since
the fissionable material can be deposited on a working
surface of one from two mutually facing detectors. The
surface-barrier and diffusion detectors with small depth
of the diffusion layer have very thin window and
therefore are suitable for detection of the short-range
fission fragments. The operating speed of detectors with
p-n-junction is also an advantage when measuring the
coincidence of the simultaneously flying out pairs
fragments. Long-continued measurements can be
carried out owing to the stability of silicon detectors
with p-n-junction.
In the track with high density of ionization, which
creates by means of fission fragment, the loss of charge
carriers is occurred. Therefore, the dependence of
amplitude of pulses for silicon detectors with
p-n-junction on the energy of fission fragment is not
linear. When comparing the pulse amplitude from the
fission fragment with the value obtained by
extrapolation of the amplitude of pulses from the
particles that create a smaller ionization density (for
example, -particles), the difference, called the
ionization defect , is determined. In this comparison the
values of the average energies for groups of light and
heavy fragments are determined using data obtained by
the method of flight time. The difference of amplitudes
corresponds to the energy, which is equal to about
10 MeV. It was determined that this difference for
group of the heavier fragments is more on 2.5 MeV
than for light fragments, and does not depend on the
type of conductivity and resistivity of silicon.
With an increase of the average electric field in the
detector from 2 103 to 2 104 V cm-1 the ionization defect
decreases by 2 times, since it is due to recombination of
carriers till to their collection. In large fields the reverse
effect was found. This effect is responsible for reduction
of the effective energy for formation of one electron-
hole pair in some parts of detector. This effect is due to
the process of reproduction, which can occur in fields
close to critical (such field is equal approximately
6 104 V cm-1 for silicon).
The semiconductor material for production of
detectors must correspond to certain conditions [12]. So,
the choice of the silicon resistivity for detectors is
caused by several of the following factors:
1) resistivity should not be too low (must be exceed
of 25 Ohm cm), since in otherwise the electric field,
which is necessary to obtain the depleted layer with the
thickness, that is equal to the fission-fragment path, may
exceed the field at which breakdown occurs;
2) if the area of the detector is large, in order to
improve the signal to noise ratio we should reduce the
capacity of detector; for this purpose the material with
higher resistivity must be used;
3) the electric field may be insufficient for full
charge collection at too high resistivity; the required
value of the field is about 104 V cm-1;
4) in the material with high resistivity the depleted
layer is too thick, which leads to the excessive noises,
high sensitivity to -rays, and also to the background
caused by fast neutrons.
The reaction cross-sections and angular distributions
of the fragments in the fission reactions caused by
charged particles are measured by means of silicon
detectors with p-n-junction. The observed cross-
sections, as a rule, are small, so a large solid angle is an
important advantage of the detectors with p-n-junction.
Three detectors with p-n-junction, situated around the
target, are used for convenience to observe the triple
fission, induced by the neutrons. Meanwhile the
-particle is emitted, besides the two large fragments.
Thanks to the operating speed of detectors with
p-n-junction and the ability to easily separate the
impulses from alpha-particles, such detectors can be
successfully used to measure the dependence of the
fission yield on the neutron energy by the method of
flight time.
The surface-barrier detectors of total absorption
energy of charged particles (E-detectors) with a wide
range of the thicknesses of sensitive area and the
detectors of the specific energy losses (d /dx-detectors)
are used for nuclear radiation spectrometry.
Modern detectors, for the most part, are not used
alone, but as constituent parts of the large detecting
LHC collider (CERN, Switzerland); at the Tevatron
collider, at the electron-positron colliders] [13 15].
In view of the above, the aim of this work was to
optimize the surface-barrier technology of the
manufacturing of sectional detector matrixes based on
the carried out comprehensive studies of the electrical
characteristics of the initial n type conductivity silicon
plates of large diameter and the definition of features of
physical processes in the surface-barrier structures.
1. METHODS OF MANUFACTURING
OF SILICON DETECTORS IN HISTORICAL
RETROSPECTIVE
There are a number of methods for obtaining the
detectors on the basis of silicon n- and -type
conductivity. In Refs. 16, 17 the diffusive technology
was used to obtain detectors of the specific energy
losses of charged particles (about 50 m). The initial
material was -Si with a resistivity = 5 kOhm cm. The
phosphorus diffuses into -Si. The gold, sputtered on
the planished surface of the crystal, served as contact to
the back side.
The planar -n-junction of controlled depth can be
obtained by diffusion method; meanwhile the thickness
of the input window of finished detector will be half
of the diffusion depth 18 . The main disadvantage of
this method is the significant reduction in the minority
carrier lifetime in silicon during heating in the process
of high temperature diffusion of phosphorus and
hereupon increasing of the reverse current of
-n-junction.
The surface-barrier technology for manufacturing of
semiconductor detectors, proposed in Ref. 19 ,
received the wide spread occurrence.
Detectors of the specific energy losses with
thickness of 50 m were produced by authors 20 on
the basis of combining the surface-barrier technology
with the diffusive technology at using passivation by
oxide. In this paper the principle of uniform etching in
the slow etchant was proposed. The sample is carefully
plane-parallel planished with the accuracy of 0.75 m,
since this thickness spread determines the limiting
spread after etching of the sample. Cup with the etchant
rotated with a rate of 12 revolutions per minute and was
inclined at the angle of The sample was mounted
on the teflon disk with the rotation axis of disk, which is
perpendicular to the rotation axis of cup. The etchant
1 HF:20 HNO3 with volume about 250 cm3 was used. In
this system each part of the central surface of sample
moves relative to the etchant with the same average rate.
The etching rate was 1.2 m/min. In order to remove
the structural imperfections after grinding, the etching
time was chosen on the basis of removal of 75 m from
each side of the crystal. The fluctuation of crystal
thickness in typical samples was 0.75 m. The area of
constant thickness is located in a central part of the
crystal and was equal approximately 2 cm2. The sample
had the profile view as I-beam. This fact added to it the
mechanical strength [Note. I-beam or H-shaped is the
profile (cross-section in the form of two letters T);
I-beam provides a high resistance to loads for the whole
construction under the significant mechanical effects].
In this paper the problem of particle channeling in
the thin detector was first discussed. Anomalous energy
losses of the charged particles along the directions of
the crystallographic axes and planes degrade the energy
resolution of detectors and the separation on the masses
with help of telescopes.
In Ref. 21 the energy losses of charged particles in
silicon depending on the track orientation were
investigated, and the special cutting of crystals for
plane in order to avoid the phenomenon of channeling
was proposed.
Authors of Ref. 22 have successfully used the
surface-barrier technology for obtaining detectors of the
specific energy losses with thin windows . The initial
material was the high-resistance Si, the thickness of
detectors was 70 m.
Concept of the drift of lithium ions in the electric
field of reverse bias junction showed the ability of
substantial increase in sensitive area of the detector at
the low resistivity of the initial p-Si. In Refs. 23, 24
/dx-detectors, fabricated on the basis of silicon,
compensated by lithium, were described. Such method
is allowed to receive detectors with the thin windows
and the width of the sensitive area from hundreds of
microns to several millimeters at low operating
voltages.
From the literature data it can be concluded that the
n-type silicon is suitable as the initial material for
manufacturing of the detectors of specific losses with
the small thicknesses (less than 100 ), and the
p-type silicon, compensated with lithium by means of
the method of the ion drift, is suitable for detectors of
medium and large thicknesses (above 100 m).
Meanwhile the surface-barrier technology of fabrication
of detectors in order to create a working p-n-junction
and provide the thin windows on both sides of the
detector is most promising.
The input window of the detector is determined by
the thickness of the surface layer, which is traversed by
the charged particle before it reaches the sensitive layer
(space-charge region). In Ref. 25 the thickness of
window was determined experimentally on the defect
of pulse height, obtained at comparing of the pulse
heights from the protons and -rays with the energy of
80 keV.
Fig. 1 presents the dependence of the input
window thickness x on the reverse voltage for
detectors, fabricated on the basis of n-Si with the
different resistivity. As the experiment showed, x
decreases linearly as a function of log V, and the slopes
of the straight lines are dependent on the resistivity.
When the voltage V = V0, the thickness x is zero,
where V0 is a critical shift, which is decreased with
resistivity . Thus, the empirical relationship between
the values has the following form: ,
where A and B are the constants.
100 1000
0
1000
2000
4
3
2
1
U
0
U, V
Fig. 1. For detectors made on the basis of n-Si,
dependences of the thickness of input window
on the reverse voltage U at different resistivities
, kOhm cm: 1 50; 2 10; 3 2; 4 1 25
The existence of the input window is entirely
understandable, since there is -n-junction beyond the
contact. Therefore, the depletion region extends in p-
and n-region, depending on the resistivity and applied
voltage. The window is formed from oxide layer and
the silicon layer disposed between the oxide and the
boundary of the space-charge region. The electric field
in this layer is very low and the high concentration of
impurities increases the recombination. The surface-
barrier diode structure can be formed due to the
presence of two mechanisms: a) the diffusion of oxygen
through the Au contact into the bulk of Si crystal, where
it acts as an acceptor (in this case, the surface-barrier
diode is similar to the diffused junction); b) the
adsorption of oxygen on the surface, if the electron
affinity of oxygen is higher than the work function of
semiconductor (in this case, p-type layer is created on
n-type material).
For the first case the thickness of window is
defined as
, (1)
and the value of critical displacement (at x = 0):
, (2)
where N0 is the surface carrier concentration; L the
diffusion length; and 0 are the dielectric constants of
silicon and vacuum, respectively. The depletion region
reaches Au-contact at V0.
In the second case:
, (3)
, (4)
where Nh is the hole concentration near the surface.
Authors of Ref. 25 obtain the best agreement of the
experimental data with the first model, while they notice
also the importance of the second model.
2. PHYSICAL BASE OF THE
MANUFACTURING TECHNOLOGY OF
DETECTOR MATRIXES ON THE SILICON
PLATES OF LARGE DIAMETER
In order to select the silicon plates of the electron
type conductivity of large diameter with parameters
suitable for the manufacture of detectors, the
comprehensive research of the electrophysical
properties of initial semiconductor material was carried
out, in particular, the resistivity spread along the
diameter of ingots, distribution of the dislocation
density, the lifetime of minority carriers were
determined.
The important condition at the production of
detectors of specific losses is the flatness of plates each
of them, to provide the equal energy losses of charged
particles that cross the detectors through the area of the
input windows . For the plane-parallel etching of
crystals the special apparatus was developed. Such
apparatus provides the equal access to all points of the
crystal for etchant. This fact allows reaching the
uniform rate of etching throughout the area of the plates
and forming the high-quality surface-barrier structure.
Before etching the plate was plane-parallel planished
(by means of powders with a gradual decrease in grain
size from M20 to M7), and then thoroughly washed in
the organic solvents and high-resistance water
( 3 5 MOhm). We used a number of etchants on the
basis of concentrated especially pure acids [hydrofluoric
(HF), nitric (HNO3) and acetic (CH3COOH)], combined
in the different proportions: 3HF:5HNO3:3CH3COOH
(the etchant number 1), 1HF:20HNO3:1CH3COOH (the
etchant number 2) and 17HF:110HNO3:7.3CH3COOH
(the etchant number 3). The measurement of plate
flatness was carried out on the apparatus Optimeter ,
which has an accuracy of 0.5 m. The spread in
thickness for the surfaces, etched by means of etchants
number 1 and 3, exceeded of 15 m. Therefore, these
etchants were unsatisfactory from the viewpoint of
flatness. When using etchant number 2 the flatness
reaches about 0.5 m that fully satisfied the
requirements. For used etchants the following etching
rates were obtained: for etchant number 1 2.2 m/min;
number 2 1.7 m/min; number 3 3.3 m/min, i. e.
these etchants are slow.
The state of the semiconductor surface was
controlled by techniques of measuring the field effect
and contact potential difference when forming the
surface-barrier structure. This allowed determining the
value of band bending on the silicon surface under the
different chemical treatments, as well as the kinetics of
the surface potential k and its homogeneity. In
particular, for the slow etchants number 1 3 the value of
the surface potential, measured immediately after the
etching, showed that the inversion layer is already
formed, and consequently, the effects of aging appear
weakly less for such surfaces.
It has been experimentally proved that the
distribution of the surface potential for crystal silicon,
treated by quickly etchants ( 20 m/min), is
nonuniform. The kinetics of change of the surface
potential is quite slow. The surface potential of crystals,
chemically polished by the slow etchants
( 2 5 m/min) in the made apparatus, is very uniform
( k 15 mV), in this case the equilibrium of value of
the surface potential on the surface comes quickly. The
magnitude of the band bending corresponds to the
formation of surface-barrier p-n-junction.
The important information concerning electronic
state of the real surface of n-type silicon, etched by the
different etchants, was obtained from measurements of
the field effect and the contact potential difference. This
allowed formulating some preliminary conclusions
concerning quality of the surface barrier of detector, as
follows:
1) the n-type silicon surface immediately after the
etching in the fast etchants based on the concentrated
especially pure acids (nitric, hydrofluoric and acetic),
combined in different proportions, has the electron
conductivity (small enrichment by the main carriers);
2) at the end of the etching process the strongly
depleted layer (the inversion layer on the concentration)
in the surface region was created at slow etching (the
composition of etchants was chosen another, but on the
basis of the same acids), i. e. the near-surface
p-n-junction appears;
3) the surfaces treated by the fast etchants gradually
change the enriched layer on the inversion layer in the
aging process in atmospheric conditions, i. e. the aging
time of detectors produced then on such crystals would
be very significant;
4) the concentration of the surface levels on the
chemically polished silicon surfaces is quite large and,
therefore, will lead to the screening of the external
influences and to the more stable characteristics of the
fabricated detectors of specific losses when the external
conditions of the capture of carriers on the surface
levels are changed.
The technological regime of formation (after
chemical polishing of the crystals) the back noninjecting
contact of detectors during the sequential thermal
deposition of Ge and Al thin layers on the back side of
the crystal through the 9-sector masks was developed on
the basis of the conducted researches. In this case p-Ge
with resistivity about 3 Ohm cm was used. Germanium
of p-type conductivity was sputtered at the vacuum
10-6 Torr with the evaporation rate of about 1 It
should be noted that at the lower vacuum and lower
evaporation rate, the germanium layer is saturated by
the oxygen atoms (up to about 1%), that resulting in
undesirable change in conditions on the crystal surface.
Development of the production technology for such
noninjecting contact allowed manufacturing the
detectors, capable of operating at the reverse biases,
exceeding the voltage of the total depletion of detector.
Germanium and aluminium plates were kept in the
air for two days after deposition in order to form the
stable oxide film on the real silicon surface. Thereafter
the thin layer of gold (~ 200 was deposited on the
work surface through the specially manufactured mask
for forming the surface-barrier structure.
The possibility to accelerate the formation of
surface-barrier junction by applying to the Au-Si
contact the reverse voltage of the order of the potential
barrier height was found. In this case the electric field in
the metal-semiconductor contact, without substantial
affecting on the equilibrium height of the barrier, will
accelerate the drift of the oxygen ions through the gold
film to the semiconductor surface, which results in a
more rapid formation of surface-barrier junction.
The significant influence of the environment on the
level of reverse currents of the freshly manufactured
surface-barrier structures was established as a result of
the conducted researches. It was found that if
immediately after the deposition of gold on the silicon
surface the environment of dry oxygen is created, then
the barrier is not formed and the detector has a high
reverse current, while in the atmosphere of moist
oxygen the stable surface-barrier p-n-junctions are
formed most efficiently.
The final stage of the process is the production of
frames for mounting of the detector matrixes and,
finally, the mounting of sectional detectors. Thereafter
the testing of the electrophysical and spectrometric
parameters of the experimental samples was carried out.
The measurements of the voltage-current and capacity-
voltage characteristics allow evaluating a range of
working bias of detectors, the value of the breakdown
voltage, and the level of reverse currents, which
contribute to the noise detectors.
The results of the conducted researches of bulk and
surface properties of the initial semiconductor material
became the basis for the development of manufacturing
technology of sectional detectors based on the silicon
plates of large diameter ( 100 mm). It was necessary to
create the 9-sectional detector matrixes, wherein each
section is a separate detector and they all must have the
same characteristics at the single reverse voltage.
The 9-sectional detectors with the thickness of
sensitive area W 350 m, in which each of nine
sections has the area of working surface of S = 4 cm2,
were manufactured based on the selected initial silicon
plates with resistivity = 1.5 2 kOhm cm and lifetime
of the minority carriers = 1000 s.
Fig. 2 shows the general view of the obtained
9-sectional detectors from the side of input and output
windows of sensitive area.
Fig. 3 shows the voltage-current characteristics of
the each of detectors of the typical 9-sectional matrix.
Fig. 4 shows the dependences 1/ 2 = f (V) for the
typical 9-sectional detector on the basis of n-Si from the
side of output window (the aluminum back contact).
a
b
Fig. 2. General view of the 9-sectional detector:
a from the side of input window of sensitive area; b from the side of output window
0.1 1 10 100
0.1
1
10
U, V
1
2
3
4
5
6
7
8
9
0 50 100 150 200 250
0.0
2.0x10
-4
4.0x10
-4
6.0x10
-4
8.0x10
-4
1.0x10
-3
U, V
1
2
3
4
5
6
7
8
9
Fig. 3. The reverse current-voltage characteristics
of the typical 9-sectional detector on the basis of n-Si
Fig. 4. Dependences 2 = f(V) of the typical
9-sectional detector at the basis of n-Si
apacity-voltage characteristics show that the full
depletion of the detector occurs at reverse voltage about
200 V. Current-voltage characteristics indicate that the
detector can work under the maximal reverse voltage of
about 300 V, while the electric field strength in the
detector is 2 104 V/cm. At such electric field strength
the spectrometry of heavy charged particles is feasible.
The heavy charged particles cause under absorption the
high density of the electron-hole pairs.
Fig. 5 shows the typical spectrometric characteristics
received under irradiation by the certified three-
component source of -particles ( 1 = 4.821 MeV;
2 = 5.156 MeV; 3 = 5.467 MeV) by means of
9-sectional surface-barrier detector, which demonstrate
the identity of the results obtained. The energy
resolution of the sectional detectors is equal
R 50 75 keV under irradiation by the -source.
Thus, our study of bulk and surface properties of
specially selected initial material and optimizing the
surface treatment method of silicon allowed
manufacturing the qualitative detectors with stable
parameters and the high energy resolution.
Measurements of the front duration of pulse rise,
received from the experimental detector samples
showed that the front duration is less than 5 ns, that was
an order of magnitude lower than the similar value for
detectors fabricated on the basis of silicon, compensated
by lithium. This allows to use the obtained detectors for
the schemes with the temporary binding, where it is
necessary not only the high energy resolution, but the
high temporal resolution.
0 200 400 600 800 1000
0
500
1000
1500
2000
2500
3000
Channel Number
Section 1
U = 250 V; I = 1.4
0 200 400 600 800 1000
0
500
1000
1500
2000
2500
3000
Channel Number
Section 2
U = 250 V; I = 0.96
0 200 400 600 800 1000
0
500
1000
1500
2000
2500
3000
Channel Number
Section 3
U = 250 V; I = 0.65
0 200 400 600 800 1000
0
500
1000
1500
2000
2500
3000
Channel Number
Section 4
U = 250 V; I = 0.60
0 200 400 600 800 1000
0
500
1000
1500
2000
2500
3000
Channel Number
Section 5
U = 250 V; I = 1.25
0 200 400 600 800 1000
0
500
1000
1500
2000
2500
3000
Channel Number
Section 6
U = 250 V; I = 1.20
0 200 400 600 800 1000
0
500
1000
1500
2000
2500
3000
Channel Number
Section 7
U = 250 V; I = 0.70
0 200 400 600 800 1000
0
500
1000
1500
2000
2500
3000
Channel Number
Section 8
U = 250 V; I = 1.23
0 200 400 600 800 1000
0
500
1000
1500
2000
2500
3000
Channel Number
Section 9
U = 250 V; I = 1.40
Fig. 5. The -particle spectra of the three-component source (233U, 237Pu, 241Am), obtained by means of the typical
9-sectional surface-barrier detector
CONCLUSIONS
1. The methods of chemical treatment of silicon
were developed to produce the great working planes of
detectors with homogeneous characteristics and the
formation of qualitative surface-barrier structures.
2. It was proved experimentally that at the low
etching rate and the ensuring of the conditions of equal
access of etchant to the entire surface of the crystal, the
homogeneous surface with high uniformity of the
surface potential ( k 15 mV) can be obtained that
allows to produce the high-quality detectors.
3. On the basis of the optimized surface-barrier
technology with use the high-resistance n-type silicon
plates of large diameter ( 100 mm) the sectional silicon
semiconductor detectors with the thickness of sensitive
area W 350 m, the working area S = 4 cm2, and with
the energy resolution R from 50 to 75 keV under
irradiation by means of the certified three-component
-source were developed. The manufactured detectors
can be used in the nuclear experiments involving heavy
ions at the low yields of reaction products.
4. The main electrophysical parameters and
spectrometric characteristics of the surface-barrier
silicon detectors of nuclear radiation, which enter into
the composition of the 9-sectional detector matrixes,
were determined. Detectors have identical parameters
and low reverse current at voltages of about 300 V.
Meanwhile the voltage of full depletion of the sensitive
volume of detectors was about 200 V.
5. The measurements of capacity-voltage
dependencies of all nine working sections of the
detector matrix shown that its constituent elements
(detectors) have abrupt working p-n-junction. At the
same time the electric field strength in detectors was
about 104 V/cm, which is enough for the efficient
collection of charge carriers during the spectrometry of
fission fragments of heavy atomic nuclei with high
energy resolution.
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Article received 07.11.2016
-
n- ( 100 . 9-
W 350
S = 4 2 R = 50 75
-
-
n-Si
100 9-
W 350 S = 4 2
R = 50 75 -
|