Influence of the surface electronic processes on the spectrometric characteristics of silicon detectors
In this paper the features of influence of the surface electron processes on the formation of silicon surface-barrier detector structures were founded, the regimes of chemical treatments of the surface for Si crystals were established with using of different combinations of etchants for the accele...
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| Zitieren: | Influence of the surface electronic processes on the spectrometric characteristics of silicon detectors / G.P. Gaidar, S.V. Berdnichenko, V.G. Vorobyov, V.I. Kochkin, V.F. Lastovetskiy, P.G. Litovchenko // Вопросы атомной науки и техники. — 2016. — № 2. — С. 17-24. — Бібліогр.: 11 назв. — англ. |
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irk-123456789-1153452017-04-04T03:02:25Z Influence of the surface electronic processes on the spectrometric characteristics of silicon detectors Gaidar, G.P. Berdnichenko, S.V. Vorobyov, V.G. Kochkin, V.I. Lastovetskiy, V.F. Litovchenko, P.G. Физика радиационных повреждений и явлений в твердых телах In this paper the features of influence of the surface electron processes on the formation of silicon surface-barrier detector structures were founded, the regimes of chemical treatments of the surface for Si crystals were established with using of different combinations of etchants for the accelerated creation of surface-barrier structures with stable parameters, the slow regimes of etching were developed for making the detectors of plane-parallel geometry. On the basis of experimental studies concerning the improvement of the formation processes of qualitative surface-barrier structures, the fabrication technique of the silicon spectrometric detectors was optimized; the prototypes were manufactured and their characteristics were identified. Выявлены особенности влияния поверхностных электронных процессов на формирование кремниевых поверхностно-барьерных детекторных структур; установлены режимы химических обработок поверхности Si-кристаллов с использованием различных составов травителей для ускоренного создания поверхностно- барьерных структур со стабильными параметрами; разработаны медленные режимы травления для изготовления детекторов плоскопараллельной геометрии. На основе проведенных экспериментальных исследований по совершенствованию процессов формирования качественных поверхностно-барьерных структур оптимизирована технология изготовления кремниевых спектрометрических детекторов, изготовлены опытные образцы и определены их характеристики. Виявлено особливості впливу поверхневих електронних процесів на формування кремнієвих поверхнево- бар’єрних детекторних структур; встановлено режими хімічних обробок поверхні Si-кристалів з використанням різних складів травників для прискореного створення поверхнево-бар’єрних структур зі стабільними параметрами; розроблено повільні режими травлення для виготовлення детекторів плоско- паралельної геометрії. На основі проведених експериментальних досліджень щодо вдосконалення процесів формування якісних поверхнево-бар’єрних структур оптимізовано технологію виготовлення кремнієвих спектрометричних детекторів, виготовлено дослідні зразки та визначено їх характеристики. 2016 Article Influence of the surface electronic processes on the spectrometric characteristics of silicon detectors / G.P. Gaidar, S.V. Berdnichenko, V.G. Vorobyov, V.I. Kochkin, V.F. Lastovetskiy, P.G. Litovchenko // Вопросы атомной науки и техники. — 2016. — № 2. — С. 17-24. — Бібліогр.: 11 назв. — англ. 1562-6016 PACS: 9.00.00; 29.40.Wk http://dspace.nbuv.gov.ua/handle/123456789/115345 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Физика радиационных повреждений и явлений в твердых телах Физика радиационных повреждений и явлений в твердых телах |
| spellingShingle |
Физика радиационных повреждений и явлений в твердых телах Физика радиационных повреждений и явлений в твердых телах Gaidar, G.P. Berdnichenko, S.V. Vorobyov, V.G. Kochkin, V.I. Lastovetskiy, V.F. Litovchenko, P.G. Influence of the surface electronic processes on the spectrometric characteristics of silicon detectors Вопросы атомной науки и техники |
| description |
In this paper the features of influence of the surface electron processes on the formation of silicon surface-barrier
detector structures were founded, the regimes of chemical treatments of the surface for Si crystals were established
with using of different combinations of etchants for the accelerated creation of surface-barrier structures with stable
parameters, the slow regimes of etching were developed for making the detectors of plane-parallel geometry. On the
basis of experimental studies concerning the improvement of the formation processes of qualitative surface-barrier
structures, the fabrication technique of the silicon spectrometric detectors was optimized; the prototypes were
manufactured and their characteristics were identified. |
| 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 |
Influence of the surface electronic processes on the spectrometric characteristics of silicon detectors |
| title_short |
Influence of the surface electronic processes on the spectrometric characteristics of silicon detectors |
| title_full |
Influence of the surface electronic processes on the spectrometric characteristics of silicon detectors |
| title_fullStr |
Influence of the surface electronic processes on the spectrometric characteristics of silicon detectors |
| title_full_unstemmed |
Influence of the surface electronic processes on the spectrometric characteristics of silicon detectors |
| title_sort |
influence of the surface electronic processes on the spectrometric characteristics of silicon detectors |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2016 |
| topic_facet |
Физика радиационных повреждений и явлений в твердых телах |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/115345 |
| citation_txt |
Influence of the surface electronic processes on the spectrometric characteristics of silicon detectors / G.P. Gaidar, S.V. Berdnichenko, V.G. Vorobyov, V.I. Kochkin, V.F. Lastovetskiy, P.G. Litovchenko // Вопросы атомной науки и техники. — 2016. — № 2. — С. 17-24. — Бібліогр.: 11 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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2025-07-08T08:38:01Z |
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| fulltext |
ISSN 1562-6016. ВАНТ. 2016. №2(102) 17
INFLUENCE OF THE SURFACE ELECTRONIC PROCESSES ON THE
SPECTROMETRIC CHARACTERISTICS OF SILICON DETECTORS
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
In this paper the features of influence of the surface electron processes on the formation of silicon surface-barrier
detector structures were founded, the regimes of chemical treatments of the surface for Si crystals were established
with using of different combinations of etchants for the accelerated creation of surface-barrier structures with stable
parameters, the slow regimes of etching were developed for making the detectors of plane-parallel geometry. On the
basis of experimental studies concerning the improvement of the formation processes of qualitative surface-barrier
structures, the fabrication technique of the silicon spectrometric detectors was optimized; the prototypes were
manufactured and their characteristics were identified.
PACS 29.00.00; 29.40.Wk
INTRODUCTION
Semiconductor detectors occupy an important place
among devices of nuclear spectrometry and are used to
study the spectral composition, intensity, spatial and
angular distribution of ionizing particles [1]. Silicon is
the most attractive material for producing detectors due
to the developed silicon technology and the ability to
create not only the dosimetric and radiometric but also
the spectrometric detectors. Semiconductor detectors on
the basis of silicon are used for the detection of charged
particles and -rays with the energy of 100 keV.
The semiconductor detectors are divided into
surface-barrier Au-Si, diffusion with (p-n)- and (n-p)-
junctions, respectively, and drift-diffusion of p-i-n-type
depending on the parameters and the manufacturing
technology. A significant advantage of the surface-
barrier detectors, manufactured on the basis of silicon
(as opposed to the detectors on the basis of germanium),
is their ability to operate at room temperature without
any special cooling.
The rapid development of fabrication industry of
semiconductor detectors led to the appearance of large
quantity of the nuclear radiation counters and
spectrometers designed to solve the concrete problems
in the various fields of the fundamental and applied
research of the modern physics. Detectors are used in
the nuclear physics, at study of cosmic space, in
biophysics, geophysics, medicine and other fields of
science and technology, which use the radioactive
radiation [2, 3]. Semiconductor detectors have important
qualities, such as high energy resolution, linearity of
characteristics over a wide range of energies for
different particles, small time of pulse rise, insensitivity
to the magnetic fields, compactness, mechanical
strength, the ability to operate at low temperatures, etc.
Today the semiconductor detectors provide the best
accuracy in determining of the particle coordinates in
the large detection systems, capable of operating at very
high magnetic fields, and in the fairly hard radiation
conditions, which is especially important for the large-
scale experiments to study rarest processes (in
particular, the experiments on American Tevatron
Collider) and the experiments at the Large Hadron
Collider.
Among the wide class of the nuclear radiation
detectors on semiconductor crystals the silicon-lithium
detectors [Si(Lі)-detectors] with the thickness of
sensitive area from 2 to 7 mm occupy a special place.
These detectors are the basic spectrometric elements at
the registration of the long-range charged particles with
the energy of 100 MeV [4–6]. Such detectors are the
structure with p-i-n-junction formed by diffusion of
lithium in the semiconductor silicon plate of p-type
conductivity. Lithium is the shallow impurity which is
used to produce the highly compensated i-areas of
silicon nuclear radiation detectors. Meanwhile, the
compensation was carried out by the electric drift of
lithium from thin surface layer. In this layer the
preliminary introduction of lithium was carried out at
500…600
о
С during about 5 min with a sharp further
cooling, while the drift of lithium was carried out at
65…100
о
С. The literature data concerning the diffusion
coefficient of lithium are characterized by the straggling
of several orders not only in silicon, but also in other
semiconductors. This fact is explained by the effective
interaction of lithium (under the diffusion in the
interstitials) with background impurities and defects,
which are introduced during the growth, as well as
during the thermal and other material treatment [7].
Thus, the development of semiconductor nuclear
radiation detectors with high energy resolution and
position resolution, with signal linearity over a wide
range of energies for different types of particles are
closely connected with the properties of the initial
crystal, in particular, with the presence of the impurity
inhomogeneities in its bulk. In addition, when creating
detectors we should take into account a set not only
physical, but also technological, and design features.
These features connected with manifestation of the
effects caused by the interconnection of the parameters
of initial crystals with the manufacturing technology of
the effective nuclear radiation detectors on their basis,
as well as with characteristics of the obtained detectors.
Therefore, it is necessary not only deeply understand
physics of the phenomena that occur on the surface and
in the bulk of silicon crystals, but also to be able to
purposely control the complex technological processes
(diffusion, drift, chemical and mechanical treatments).
18 ISSN 1562-6016. ВАНТ. 2016. №2(102)
Finally, the detector structures (such as p-n or p-i-n)
must have optimal noise, capacitive, current
characteristics that provide the effective radiometric
parameters (energy resolution, qualitative amplitude
signals, high sensitivity, thin input “windows” – “dead
layers” etc.).
In view of the above, the aim of this research was
definition of the physical nature of basic processes in
structures with the surface potential barrier on the high-
resistance silicon to optimize the manufacturing
technology of high-quality test samples of nuclear
radiation detectors with stable characteristics for
nuclear-physics experiments.
1. FEATURES OF PHYSICAL PROCESSES
OF THE FORMATION OF SURFACE-
BARRIER STRUCTURES
The surface-barrier structures are an integral part of
the many types of semiconductor detectors. In
semiconductor spectrometer the measured energy range
are determined by the thickness of the sensitive layer,
which depends on the type of detector. Since the entire
sensitive volume must be available for the charged
particles, and the width of the “dead layer” should be
minimal, p-n (or n-p)-junction must be created near the
surface of the crystal. This can be done in two main
ways. 1). Surface diffusion of substance with added
impurity of one type deep into the crystal, which has a
low impurity concentration of another type.
2). Formation of an artificial surface barrier by using the
chemical properties of the surface in pure n-silicon.
Detectors with diffusion junctions can be obtained
by the diffusion of phosphorus from gaseous or solid
state into the p-type silicon crystals. In the latter case
Р2О5 are applied directly on the silicon surface, and then
placed in a furnace. The depth of penetration of
impurities can be controlled by the duration of the
diffusion process and the temperature at which this
process occurs.
It can be done similarly, if the p-type covering
should be applied on the n-type material, which serves
as the main body of the detector. However, in this case,
instead of having to create a surface layer of p-type by
thermal diffusion of the chemical contaminations, it is
more reasonable to use the chemical properties of n-Si
surface. The surface layer of n-Si is easily oxidized, and
behaves as electron acceptor (p-layer). The electrical
contact with the surface layer (the inversion area) is
performed by the layer of metal (usually, gold), which is
applied to the semiconductor surface by sputtering in a
vacuum. Nonoperating (“dead layer”) of the gold film
on the surface is very thin and makes up about 3
-6
cm. In
the contact of metal and real surface of silicon (metal-
semiconductor) the surface-barrier structures form the
working p-n-junction, which creates a sensitive volume
of the detector under reverse voltage. In such detectors
the thickness of sensitive area can be varied by
changing of reverse bias voltage that allows carrying out
the separation of charged particles for paths and
ionization density.
Since the temperature regime of manufacturing of
the surface-barrier rectifying contact and the
noninjecting rear contact does not exceed of 100
о
С, it
allows to save the value of the lifetime of minority
charge carriers ( ) and create the detectors with high
energy resolution (R).
It should be noted that the modern detectors with
implanted p-n-junctions are heat treated at temperatures
800 °С to anneal the radiation defects that leads to the
reduction of the lifetime of minority charge carriers and
the deterioration of the energy resolution, including the
expense of considerable thickness of the input
“window”.
The physical processes, which control the
characteristics of surface barriers, are quite complex. At
present, it becomes increasingly clear that the surface
states are the dominant controlling factor of rectifying
characteristics, rather than the difference in the work
functions from the metal and semiconductor. The type
(donor and acceptor), the concentration and the energy
position of the fast and slow surface states determines
the potential of semiconductor free surface and the
surface, which is directly under the metal electrode.
Properties of the chemically etched Si surfaces in
different environments have largely studied already, but
the results of the experiments are very different. For
example, it can be extracted the following regularities
for the etched silicon surfaces in the mixture of nitric
(HNO3) and hydrofluoric (HF) acid:
1) immediately after etching the surface is unstable,
but the stability increases when exposed to air;
2) in the neutral environment (vacuum) the surface
will be of weak n-type for n-type material;
3) the environment with a high electron affinity
[Note. The electron affinity is the energy that is needed
in order to take away an electron from the single
negatively charged ion, eV/atom; the similar energy
released when an electron is captured by the neutral
atom or molecule], such as oxygen or ozone (О3),
creates the shift of the surface potential to the p-type
surface, while the ammonia, water vapor, HF vapor
creates the shift to the n-type surface;
4) the surface properties can be modified by
chemical treatment.
In early work with surface-barrier detectors it has
been found that the Au-Si surface barriers reveal the
aging effects that are sensitive to hostile environments,
and often exhibit the deterioration of properties after
exposure to high vacuum. But it is also known that the
special chemical treatments give the good diodes (stable
in vacuum) without a long aging.
In Ref. 8 the role of the magnitude of metal work
function in the surface-barrier detectors was
investigated. The absence of definite connection
between the metal work function and the degree of
rectification was found as a result of carried out
experiments. In fact, if the aging occurs during long-
continued time, all studied metals, including with the
very low work function, create the good diodes.
However, the lowest reverse currents, the minimal aging
time and the best energy resolution were obtained only
with metals such as Au, Cr, Pt. The work function of
these metals is greater than of silicon. According to the
authors, the electric field that arises from the difference
in the work functions, is the best for electronegative or
electropositive impurities and promote the adsorption or
ISSN 1562-6016. ВАНТ. 2016. №2(102) 19
decelerate of it. In this case, the electric field promotes
the adsorption of oxygen on the surface of the detector.
Therefore, the aging time of diodes with Pt-, Cr-, and
Au-contacts are a few days, compared to the several
months for metals with the lower work function than in
Si.
The surface states are controlled by the chemical
treatment of the surface and by the environment. In
Ref. 9 shown that the layer is formed immediately
after etching on the semiconductor surface. The
thickness of this layer depends on the chemical, which
was used in order to “quench” of the etch reaction. This
layer was much more at “quench” by deionized water
(the film thickness of 100…200 Å), than at surplus of
nitric acid HNO3 with further washing in deionized
water (the film thickness of 10…20 Å). It is believed
that this film is the form of silicon hydride or elemental
silicon, but is not oxide. Such film can be a place of
localization of the fast surface states.
In Ref. 10 the classification of factors that control
the properties of the surface rectifying barriers is
presented in order of importance: 1) the surface
treatment; 2) the adsorbed gases; 3) the difference in
work functions. The theoretical model of the
semiconductor-metal contact (which takes into account
the presence of two intermediate layers, inner and outer
surface states) was also presented.
The surface-barrier detectors that have a thin input
“window” are used for registration and spectrometry of
charged low-energy particles (< 1 MeV) with small
path. The input “window” of detector is determined by
the thickness of the surface layer, which is intersected
by the charged particle before it reaches the sensitive
layer (the space-charge region). The dependence of
capacitance and thickness of sensitive layer on the
reverse-bias voltage value, and a limited magnitude of
sensitive layer (up to 2…3 mm), which depends on the
resistivity of the initial material, are the disadvantages
of detectors with thin input “window”. Si(Lі)-detectors
are used to measure the spectra of the particles of higher
energies.
2. OPTIMIZATION OF PROCESSES OF THE
FORMATION OF SURFACE-BARRIER
STRUCTURES WITH STABLE
CHARACTERISTICS
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 (dЕ/dx-detectors)
are used for nuclear radiation spectrometry. The
thickness of sensitive area of dЕ/dx-detectors is much
lesser than path of the identifiable particles.
The thin silicon detectors, the ionization chambers
and the proportional counters can be used as dЕ/dx-
detectors; silicon detectors or detectors on the basis of
high purity germanium (HP Ge) can be used as
Е-detectors.
The method of manufacture of dЕ/dx-detectors must
satisfy a number of conditions. The main condition is
the obtaining of the high plane-parallel plates of
crystals, since the fluctuations of particle energy losses
due to the nonuniformity of thickness should be smaller
than the statistical fluctuations of the charge, which is
released by the particle in the thin detector. With
decreasing of detector thickness the technological
complexities are increased (even negligible changes in
the thickness can lead to straggling in the energy losses
of the flying particles), since the thin silicon plates is
very brittle, that complicates their processing and using
in the experiment. The thin silicon plates are
manufactured by using precision grinding and etching.
Furthermore, at full depletion of the detector volume
(at the increasing of reverse bias on detector) when the
space-charge region extends to the rear contact (which
must necessarily be noninjecting) the detector must
have a low noise level. The detector of specific energy
losses should also have the thin input and output
“windows”, because the uncontrolled losses of charge
take place in these “windows”.
The detector of specific energy losses should have
the high resolution, which can be obtained under the
condition of high electric field strength in detector.
The basic parameters of dЕ/dx-detectors, such as the
level of reverse currents, the quality of the surface
barrier, the thickness of the input “windows”, and,
finally, the energy resolution, are directly related to the
properties of the initial semiconductor material and the
electronic state of its surface. Therefore, to create the
qualitative and reliable detectors with the required
parameters we must study the bulk and surface
properties of the initial silicon crystals.
Therefore, in this paper to identify the suitability of
silicon for the production of detectors, the following
parameters were investigated: the gradient of resistivity
along the ingot diameter, the lifetime of minority charge
carriers, and the concentration distribution of
dislocations. We also studied the influence of different
regimes of etching on the quality of surface-barrier
junctions and the magnitude of the input “windows” of
detectors. At forming the surface-barrier structure the
state of semiconductor surface was monitored using the
measurement techniques of the combined effect of field
and the contact potential difference. It is allowed to
determine the magnitude of bending of energy bands on
the silicon surface at the different chemical treatments,
the kinetics of the surface potential k and its
homogeneity.
It was experimentally found that for producing of
detectors with the thickness of sensitive area of
W ≤ 100 m the band-purified single silicon crystal of
n-type conductivity with resistivity of 1…2 kΩ·cm
and lifetime of the minority charge carriers of > 500 s
is most appropriate. Plates of silicon should have a
homogeneous electrophysical parameters along the
diameter (the spreading of and should be 30 %),
and to be the structurally perfect (without dislocation
and defect clusters). In order to avoid the phenomenon
of ion channeling in the direction of the main
crystallographic axis of the crystal [111], cutting of
samples from the silicon ingot was carried out at the
angle of 8
o
to this direction.
The surface-barrier technology was used under the
development of detectors. At such technology (in
contrast to the diffuse and planar technologies) the
20 ISSN 1562-6016. ВАНТ. 2016. №2(102)
silicon plates were not affected by the high temperature
treatment, which, as a rule, leads to a considerable
reduction of the lifetime of minority charge carriers and
the deterioration of the energy resolution of detectors.
The carried out studies have shown that the
magnitude of surface potential varies with the lapse of
time after the chemical treatment of silicon and reaches
in certain surrounding atmosphere the stationary value
in the depending on the etching rate and the type of
substance, which was used in the “quenching” of the
etching reaction. It is found that at the end of the etching
reaction with using of nitric acid (HNO3), instead of
H2O, the oxidation rate decreased significantly, and on
the real Si surface formed more thin oxide ( 20 Å).
The opportunity to accelerate the stabilization of
surface processes by applying to the Au-Si contact the
reverse voltage of 0.6 V (i.e. the order of magnitude
of the potential barrier height) was found as a result of
the carried out experiments. Thus, 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.
Fig. 1 shows the influence of the environment
(vacuum (I), moist oxygen (II)) on the level of reverse
currents of the freshly manufactured surface-barrier
Au-n-Si structures.
10
-1
10
0
10
1
10
2
10
3
10
-8
10
-7
10
-6
10
-5
10
-4
3
2
II
t
2
I r
ev
,
A
t, min
t
1
I
1
Fig. 1. Kinetics of changes of the reverse current Іrev
of the surface-barrier Au-n-Si diode ( = 2 kΩcm,
U = 50 V) in the different atmospheres:
I – vacuum; II – moist oxygen. In the different parts
of curve II the rate of surface recombination s, cm/s is:
1 – 1; 2 – 2.4; 3 – 0.23
It was established experimentally that if immediately
after the deposition of gold on the silicon surface the
environment of dry oxygen was created, then the barrier
is not formed and the detector has a high reverse current
(see Fig. 1, curve I). When starting of the moist oxygen
the current at the beginning increases slightly with a
small time constant t1, and then gradually decreases (see
Fig. 1, curve II). Probably, t1 corresponds to the time
that required for the diffusion process of oxygen
through the metal layer to the semiconductor surface.
Oxygen can be adsorbed in the form of O2, i. e. the
oxygen molecule captures an electron. The mechanism
of Н2О (Н2О)
+
+ е
–
, О2 + е
–
2O is possible as
well. Thus, the experiment showed that the most
optimal formation of the high-quality and stable
surface-barrier p-n-junctions occurs at the aging of
structures in the atmosphere of moist oxygen.
It was revealed that in the surface-barrier detectors,
in which the space-charge region W extends through the
entire thickness of the crystal, the heterogeneity of
surface charge leads to the considerable inhomogeneity
of W that substantially impairs the energy resolution of
detectors.
It was proved experimentally that at the low etching
rate ( 5 m/min) 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.
As noted, one of the important requirements to
dE/dx-detectors is the plane-parallel plates for each of
them to provide the same energy losses of charged
particles, which cross of detectors through the area of
input “windows”. To achieve this aim the etchant must
satisfy the following requirements: a) to create on the
plate surface such charge (in magnitude and sign),
which would corresponds to the formation of the surface
barrier; b) has uniform rate of etching on the area of
plate with minimal surface relief.
For the plane-parallel etching of crystals the plant
with two movements of the crystal has been developed:
the rotation of the cup with etchant, inclined at the angle
of 30°, with a rate of 60 revolutions per minute, and
the rotation of the crystal in etchant on the special basis.
Meanwhile, the same access of etchant to all points of
the crystal is achieved, that ensures a uniform rate of
etching over the entire area of plates.
Before etching the plate is plane-parallel planished
(by the powders with a gradual decrease in grain size
from M20 to M7), and then thoroughly washed in the
organic solvents and the high-resistance water
( 3…5 MΩ). A number of etchants on the basis of the
superpurity concentrated acids [hydrofluoric (HF), nitric
(HNO3) and acetic (CH3COOH)], combined in the
different proportions, was used. The surface relief after
etching was checked on profilometer with the recording
on a recorder chart. The radius of curvature of the
diamond probe was 10 m. The smallest surface relief
( 0.5 m) was observed at treatment by the etchant of
1HF : 20HNO3 : 1CH3COOH, whereas the other used
etchants resulted in appearance of the strong relief of
surface ( 5…15 m). Therefore, from the viewpoint of
a plane-parallel, these etchants were unsatisfactory.
To create detectors with thickness of sensing area
W 200 m the rapid etchants (with the etching rate of
~ 20 m/min) were applied. The freshly etched silicon
surface was slightly depleted with significant
inhomogeneity of k, as shown by measurements of the
surface potential. The required value of к and the
inversion at the surface are reached in two days after
ISSN 1562-6016. ВАНТ. 2016. №2(102) 21
aging of plates on air. Based on these results, the
formation of a potential barrier in the metal-
semiconductor contact (by thermal deposition of gold)
was carried out after aging the plates during the
indicated time taking into account the kinetics of surface
potential k.
The etchants with small etching rate ~ 3.5 m/min
(the composition of etchants was selected on the basis
of HF, HNO3, and CH3COOH) were used for chemical
polishing of the crystals to produce thin detectors with
W ≤ 100 m. It was determined that under these
conditions the value of the surface potential k in two
hours after treatment will have a stable value, which is
corresponded to the weak inversion of conductivity for
the high-resistance silicon.
In addition, at manufacturing of detectors with
W ≤ 100 m the sequential etching technology was used
at the beginning from the rear side of plate and then
from the front side of crystal to a certain depth (50 and
150 m, respectively). To ensure the noninjecting rear
contact, the thickness of the etching layer was fitted as
follows: the reached value of the surface recombination
rate (s) should correspond to the optimal value of the
effective lifetime of minority charge carriers (τef). It
should be noted that in the finished detector the
effective carrier lifetime connect with the surface
recombination rate by the expression of
0
1 1 2
ef
s
w
, where 0 is the lifetime of minority
charge carriers in the crystal bulk, w is the thickness of
the plate. The measurement results of τef in thin plates
by the method described in Ref. [11] gave the value for
τef about 500 s.
The carried out studies allow to establish the
possibility of forming the noninjecting rear contact of
detectors by means of the thermal deposition of Ge and
Al thin layers on the rear side of the crystal, which has a
certain value of the surface recombination rate. After
the chemical polishing of crystals, through a certain
time, the germanium (~ 50 gcm
-2
) and aluminum
(~ 30 gcm
-2
) layers were sequentially deposited to the
rear surface by the method of thermal evaporation.
Germanium with p-type conductivity and resistivity of
~ 3 Ωcm was used. The germanium layer was applied
under high vacuum (about 10
-6
Torr) at evaporation rate
of about 1 Å/s. At lower vacuum and smaller
evaporation rates the germanium layer is saturated by
oxygen atoms (up to ~ 1%), that resulting in the
undesirable change in conditions on the crystal surface.
The proposed technological regime allows to obtain the
α-Ge amorphous layer and to create a neutral surface of
Si crystal (the condition of flat energy bands on the
surface).
Thus, the evaporation on the rear side of the Ge and
Al layers allows creating detectors capable of operating
at reverse bias, which in 2…3 times exceeds the full
depletion voltage of detector. Increasing of the electric
field strength in dE/dx-detectors is necessary at using
them in the experiments with charged particles with the
high atomic numbers of Z, when the high density of
ionization in the track is created.
Measurement of the current-voltage characteristics
allowed us to estimate the range of working biases of
detectors, the value of the breakdown voltage, the level
of reverse currents, which contribute to the noises of
detectors.
After evaporation of Ge and Al and the aging of
plates in air for 2 days the gold layer (about 70 gcm
2
)
was deposited on the working surface to form the
surface-barrier structure.
The carried out analysis of configuration of the
space-charge region in the surface-barrier structures on
the high-resistance semiconductors has shown that such
structures are not pure Schottky diodes. Therefore it is
necessary to take into account the presence near the
surface the area of inversion conductivity of the
minority charge carriers. In this inversion area with high
carrier concentration the electric field strength is much
lower than in the space-charge region. Therefore, in the
inversion layer the electron-hole pairs, generated by the
charged particle, recombine before reaching the
sensitive area of detector. Under these conditions, at the
presence of input “window”, the main spectrometric
characteristic of detector (a linear dependence of the
amplitude of useful signal of detector on the energy of
nuclear particles) is distorted.
3. MAIN CHARACTERISTICS OF THE
MANUFACTURED TEST SAMPLES
OF SURFACE-BARRIER DETECTORS
The results of carried out research of the electron
processes on the silicon surface became the basis for the
development of the advanced manufacturing technology
of high-quality and stable surface-barrier detectors
based on silicon plates.
The batch of detectors with thickness of sensitive
area W = 200 m and working area S = 3.5 cm
2
(Fig. 2,a) was made on the basis of Si plates with
resistivity = 1.5…2 kΩcm and lifetimes of the
minority carriers 1000 s. The batch of detectors
with thickness of sensitive area W = 100 m and
working area S = 1.5 cm
2
(see Fig. 2,b) was made on the
basis of Si plates with resistivity = 4 kΩcm and
lifetimes of the minority carriers 1000 s.
Let us consider the main characteristics of a typical
surface-barrier detector. Fig. 3 shows current-voltage
characteristics of such detector under direct and reverse
voltage. Fig. 4 shows the capacitance-voltage
dependence, and Fig. 5 shows the dependence of
1/С
2
= f (V).
The measuring of capacitance-voltage characteristics
showed that the detectors have a sharp p-n-junction, it is
evident from the region of the linear dependence of
1/С
2
= (V). Capacitance-voltage characteristics show
that the total depletion of the detector occurs when a
reverse voltage of 60 V.
22 ISSN 1562-6016. ВАНТ. 2016. №2(102)
a b
Fig. 2. General view of the surface-barrier detectors manufactured on the basis of Si plates:
a – = 1.5…2 kΩcm, W = 200 m; b – = 4 kΩcm, W = 100 m
0,1 1 10 100
0,01
0,1
1
10
I r
ev
,
m
k
А
U, V a
0,0 0,2 0,4 0,6 0,8 1,0
10
-2
10
-1
10
0
10
1
10
2
10
3
I d
ir
,
m
k
A
U, V b
Fig. 3. For the surface-barrier detector based on n-Si plates, dependences on the bias voltage:
а – the reverse current Іrev; b – the direct current Іdir
0 20 40 60 80
0
200
400
600
800
1000
C
,
p
F
U, V
Fig. 4. Capacity-voltage dependence С = f (U)
of the surface-barrier detector (at S = 1 cm
2
)
The current-voltage characteristics shows that the
detector should work under the maximal reverse voltage
of 300 V, while the electric field strength in the
detector is 2 10
4
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. 6 shows the typical -particle spectra of three-
component source (
233
U,
237
Pu,
241
Am) for the surface-
barrier detector with thickness of sensitive area
W = 200 m.
0 20 40 60 80
0,0
4,0x10
-5
8,0x10
-5
1,2x10
-4
1,6x10
-4
2,0x10
-4
1
/C
2
,
p
F
-2
U, V
Fig. 5. Dependence 1/С
2
= f (U)
of the surface-barrier detector
Spectrometric characteristics of surface-barrier
detectors with thickness of sensitive area W = 100 m
were determined under irradiate by three-component
source from the anterior and the rear sides of the crystal
(Fig. 7). The achieved energy resolution of such
detectors R was less than 70 keV. The values of the
energy resolution coincided after irradiation of detector
from both sides. This fact defines sameness of the input
and output “windows”.
ISSN 1562-6016. ВАНТ. 2016. №2(102) 23
0 200 400 600 800 1000
0
500
1000
1500
2000
2500
3000
Channel Number
C
o
u
n
ts
/C
h
an
n
el
Fig. 6. The -particle spectra of three-component
source (
233
U,
237
Pu,
241
Am ) of the surface-barrier
detector with the thickness of sensitive area
W = 200 m when the reverse bias voltage U = 250 V
and current I = 0.65 А
CONCLUSIONS
1. A complex research of the surface and bulk
properties of the initial silicon in order to solve the
problem of the creating of spectrometric semiconductor
detectors with predetermined parameters was carried
out.
2. The methods of chemical treatment of the Si
surface by means of choice of the composition of
etchants on the basis of high-purity acids of HF, HNO3,
and CH3COOH were developed for plane-parallel
etching of silicon crystals.
3. The method of accelerated formation of surface-
barrier structures through applying a reverse voltage at
the stage of the forming of potential barrier in the Au-Si
contact was proposed.
4. It was found that after the deposition of gold on
the silicon surface the optimal formation of qualitative
and stable surface-barrier p-n-junctions occurs with
aging of structures in an atmosphere of the moist
oxygen.
5. According to the optimized surface-barrier
technology on the basis of Si plates with resistivity
= 1.5…2 kΩcm and lifetimes of the minority charge
carriers 1000 s, the detectors with thickness of
sensitive area W = 200 m and with working area
S = 3.5 cm
2
were manufactured, as well as on the basis
of Si plates ( = 4 kΩcm, 1000 s) the detectors
with W = 100 m and S = 1.5 cm
2
were produced for
using in the nuclear physics experiments.
6. The main electrophysical parameters of the
surface-barrier nuclear radiation detectors and their
spectrometric characteristics were determined.
0 200 400 600 800 1000
500
1000
1500
2000
2500
3000
3500
a
C
o
u
n
ts
/C
h
an
n
el
Channel Number
0 200 400 600 800 1000
0
500
1000
1500
2000
2500
3000
b
Channel Number
C
o
u
n
ts
/C
h
an
n
el
0 200 400 600 800 1000 1200
0
500
1000
1500
2000
2500
3000
3500
C
o
u
n
ts
/C
h
an
n
el
Channel Number
c
Fig. 7. The -particle spectra of three-component
source (
233
U,
237
Pu,
241
Am), obtained by the surface-
barrier detector with W = 100 m when irradiated this
detector from the side of: a – input “window”
(working side); b – output “window” (rear contact);
c – combined (both) spectra
REFERENCES
1. G. Lutz. Semiconductor Radiation Detectors.
Device Physics. Berlin–Heidelberg: Springer-Verlag,
2007, 353 p.
2. Yu.K. Akimov, A.I. Kalinin, V.F. Kushniruk,
Kh. Yungklaussen. Semiconductor detectors of nuclear
particles and their application. M.: “Atomizdat”, 1967,
256 p.
3. S. Kim, S.H. Park, J.H. Ha, S.Y. Cho, Y.K. Kim.
Characteristics of Silicon Surface Barrier Radiation
Detectors for Alpha Particle Detection // Journal of the
Korean Physical Society. 2008, v. 52, N 6, p. 1754-
1758.
4. M.G. Gornov, Yu.B. Gurov, P.V. Morokhov,
S.V. Lapushkin, V.A. Pechkurov, B.A. Chernyshev,
V.G. Sandukovsky, E.A. Pasyuk. Multilayer
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rich nuclei // Nucl. Instr. Meth. Phys. Res. A. 2000,
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V.V. Timkin, V.V. Tsupko-Sitnikov, V. Vorobel,
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Rectifying Process in Surface Barrier Counters // IEEE
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Статья поступила в редакцию 11.01.2016 г.
ВЛИЯНИЕ ПОВЕРХНОСТНЫХ ЭЛЕКТРОННЫХ ПРОЦЕССОВ
НА СПЕКТРОМЕТРИЧЕСКИЕ ХАРАКТЕРИСТИКИ КРЕМНИЕВЫХ ДЕТЕКТОРОВ
Г.П. Гайдар, С.В. Бердниченко, В.Г. Воробьев, В.И. Кочкин, В.Ф. Ластовецкий, П.Г. Литовченко
Выявлены особенности влияния поверхностных электронных процессов на формирование кремниевых
поверхностно-барьерных детекторных структур; установлены режимы химических обработок поверхности
Si-кристаллов с использованием различных составов травителей для ускоренного создания поверхностно-
барьерных структур со стабильными параметрами; разработаны медленные режимы травления для
изготовления детекторов плоскопараллельной геометрии. На основе проведенных экспериментальных
исследований по совершенствованию процессов формирования качественных поверхностно-барьерных
структур оптимизирована технология изготовления кремниевых спектрометрических детекторов,
изготовлены опытные образцы и определены их характеристики.
ВПЛИВ ПОВЕРХНЕВИХ ЕЛЕКТРОННИХ ПРОЦЕСІВ
НА СПЕКТРОМЕТРИЧНІ ХАРАКТЕРИСТИКИ КРЕМНІЄВИХ ДЕТЕКТОРІВ
Г.П. Гайдар, С.В. Бердниченко, В.Г. Воробйов, В.І. Кочкін, В.Ф. Ластовецький, П.Г. Литовченко
Виявлено особливості впливу поверхневих електронних процесів на формування кремнієвих поверхнево-
бар’єрних детекторних структур; встановлено режими хімічних обробок поверхні Si-кристалів з
використанням різних складів травників для прискореного створення поверхнево-бар’єрних структур зі
стабільними параметрами; розроблено повільні режими травлення для виготовлення детекторів плоско-
паралельної геометрії. На основі проведених експериментальних досліджень щодо вдосконалення процесів
формування якісних поверхнево-бар’єрних структур оптимізовано технологію виготовлення кремнієвих
спектрометричних детекторів, виготовлено дослідні зразки та визначено їх характеристики.
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