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Physical chemistry of processes at the multicomponent substance solution boundary. Composition and surface structure
© Zarubina Oksana Nikolaevna,1+ Mokrousov Gennady Mihajlovich,1*
Bekezina Tatyana Petrovna,1 and Naiden Evgenii Petrovich2
1
Analytical Chemistry Division. Tomsk state university.
Lenina, 36. Tomsk, 634050. Russia. Tel.: (3822) 42-07-83.
E-mail: zon@ mail.tsu.ru , [email protected]
2
Physical faculty. Tomsk state university.
Lenina, 36. Tomsk, 634050. Russia.
____________________________________________________
+
* Leading a direction; Keeping up a correspondence
Keywords: interphase transformations, thermodynamics, potential-determining reactions, electrode
potential - рН diagrams, III-V arsenide and antimonide, a superficial phase layer, diffusion kinetics,
near-surface crystal layer.
Abstract
Using the previously made assumption of a quasi-balance establishment at the multicomponent III-V
compound − Н2О (рН) boundary and selective, uniform, and pseudoselective destruction (dissolution,
oxidation) of substances, a possible set of potential-determining reactions is specified, the values of their
potentials are calculated, and the electrode potential − рН relationships (Pourbaix diagrams) are constructed.
On this basis, the concept is constructed, allows predicting the variants of structure of the superficial phase
layer, capable to be formed in the conditions of treatment of semiconductor surface without and with electric
field exposure at the different values of electrode potentials and рН. It is shown, that equilibrium with respect
to the electronegative component (A) is shifted to the anode direction, therefore, at the boundary
semiconductor − a superficial phase layer (or electrolyte in the absence of the last) the near-surface crystal
layer is formed depleted by the component A. Using the diffusion concepts its thickness is calculated; it can
range from 5 to 500 nm. The presence of such layer is detected by results of the X-ray diffraction.
Introduction
From the thermodynamic position, the interphase boundary was considered by Gibbs [1] as a
surface of discontinuity («a transition layer»), in this layer there is a gradient of properties and
composition determined by external conditions. The two-dimensional crystal phases formed on the
surface of substances in an ultrahigh vacuum are the most studied [2]. The composition and structure
of two-dimensional phases as applied to specific substances in a liquid medium are theoretically and
practically little investigated. A substance is usually contacts with medium (liquid, gas, or solid
phases). Therefore, the interphase boundary can be considered as a component part of the reaction
zone. Depending on the activity and nature of the substance and environmental factors, at the
interphase boundary there can be various phenomena: a physical and chemical sorption, interaction
of sorption products with a substance matrix, diffusion in a solid phase, and others. These
phenomena (transformations) for each specific steady-state condition will define finally a chemical
compound, structure, properties, and dimension of an interphase boundary (a surface of a substance).
Unlike the elemental forms of substances, the processes at the surface of multicomponent crystal
compounds, and, accordingly, composition and structure of interphase boundary, will be more
complicated. Reorganization on such interphase boundaries is considered thermodynamically in [3].
It is shown, that the interphase boundary consists at least of two layers: a superficial phase layer and
a transition (near-surface) crystal layer with the destroyed stoichiometric ratio of components.
The composition and structure of the interphase boundary (surface) have a decisive influence
on the physico-chemical and electrophysical properties of substances [4, 5] (especially, on the
substances with low-dimension structure), and on parameters of materials and devices, for example,
г. Казань. Республика Татарстан. Россия. __________ ©Бутлеровские сообщения. 2011. Т.24. №3. _________ 61
Full-text research publication __________________
Mokrousov G. M., Zarubina O. N., and Bekezina T. P.,
and Naiden E.P.
widely applied in electronics metal-oxide-semiconductor structures (MOS structures); metalsemiconductor structures (Schottky barriers); InAs/GaInAs, GaAs/GaInAs semiconductors, and
others heterostructures. It is necessary to know the mechanisms of formation of a thermodynamically
stable superficial phase oxide layer without a transition (near-surface) broken crystal layer, a nearsurface crystal layer of the semiconductor with controllable stoichiometry, and interphase boundary
(surface) without a superficial phase layer. The particular interest is represented the possibilities the
formation of nanoscale superficial structures under normal conditions, for example, by chemical or
electrochemical treatment of crystalline semiconductors in a liquid medium [6, 7, 8] with a
controllable selective removal of one of the components and introduction of other component of the
compound semiconductor (solid solution). Realization of such approach is impossible without the
development of the general physico-chemical conception about the transformations on interphase
boundary the semiconductor − aqueous (non-aqueous) process medium, and methodology of the
description of formation process, forecasting, and estimation of composition and structure of the
surface of multicomponent crystal substance.
Calculation results and their discussion
The superficial phenomena in the water (рН) – multicomponent crystal substance (III-V
compounds) system are investigated for a long time, but the formation mechanism and the structure
of the interphase boundary in connection with the treatment conditions of materials are not
developed completely. In the present work are considered the development of the formation concept
of the surface of a multicomponent crystal substance. This concept is based on the thermodynamic
representation about the destruction mechanism (dissolution, oxidation) of substances and
corresponding potential-determining reactions proceeding under conditions of an establishment of
quasi (steady-state) equilibrium.
To represent all variety of phenomena the end result of calculations is considered by us in the
form of the quasi equilibrium electrode potential – рН of the aqueous medium graphic dependence
(Pourbaix diagrams). For choice of the basic transformations and simplification of the graphical
representation the following approximations, usually accepted in the calculation and construction of
Pourbaix diagrams [9] for elemental forms of substances, is supposed. It is assumed that in the
system there are no foreign substances, capable to form complexes and insoluble compounds (except
of oxides and hydroxides) with the components of the considered material, it is also assumed that
there are no substances, including dissolved molecular oxygen, capable to initiate the corrosion
process. The semiconductor properties of the material (conductivity type, carrier density, the
possibility of photogeneration of carriers, and the distortion because of this of the value of electrode
potential) are not considered here; it is fully justified if to select for experimentation the narrow-gap
(InSb, InAs) or wide-gap (GaAs) semiconductor with high carrier density.
For the description of process of destruction of solid bodies (self-dissolution, corrosion) in the
liquid medium in many cases the electrochemical representations are used [10]. It is supposed that at
the surface the opposite directed coupled electrochemical processes are possible: anode (transition of
the components of solid body into the solution or formation of insoluble forms of substances), and
cathode (as a rule, the reduction of oxidants). In combination these processes influence on rise of
electrode potential jump at the interface boundary. If for simplification neglect the possibility of
corrosion of substances (cathode reactions) at standard conditions, select the possible potentialdetermining reactions at the interface boundary, and calculate the corresponding values of the
electrode potentials (Еeq), it is possible to evaluate the products of transformations and the possible
composition of the solid surface.
Possible types of equilibrium states and the forms of substances in the elementary solid body −
water (рН) systems are in detail considered in [11]. The most interesting approach to the description
of such equilibrium was developed by M. Pourbaix [9] by means of diagrams in the coordinates
Eeq –рН of water solution, later called Pourbaix diagrams. To construct these diagrams, a possible
set of redox states of the substance and the solubility of its oxidized forms is revealed as a function
of рН, the values of the Gibbs energy (∆G) and standard equilibrium potentials ( Eeq0 ) of the
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PHYSICAL CHEMISTRY OF PROCESSES AT THE MULTICOMPONENT SUBSTANCE-SOLUTION…– ___ 61-69
corresponding potential-determining reactions are calculated ( Eeq0 = -∆G/zF, where z is the number
of electrons involved in the reaction; F is the Faraday constant equal to 96491.2 C or 96.55
kJ/V·mol). Relationship of Eeq with the activity of the oxidized and reduced forms of substances
involved in the reaction is found from the Nernst equation ( Eeq = Eeq0 +(0.059/z) lg [ox.]/[red.]).
By comparing the calculated and experimentally measured values of the stationary electrode
potential Est of substances in the etching solution, from a large number of thermodynamically
possible potential-determining reactions, the most probable reaction can select. Using such approach
can simply and quickly estimate the possible forms (phase) of the substance that may be present on
the surface and in solution.
The equilibrium in the GaAs−H2O (рН) system with application of the specified approach is
discussed in [12, 13]. The allowability of its application and transferring of received conclusions
concerning the individual state of solid bodies on their multicomponent substances by authors is not
proved. At the same time, the calculations show, that the calculated value Eeq of the multicomponent
compounds lies between values of calculated equilibrium potentials of its components (EeqA < Eeq <
EeqB). It follows from this that the considered equilibrium is irreversible: for the component A (Ga,
In) it is shifted to the anode region, and for the component B (As, Sb) it is shifted to the cathode
region.
As the equilibrium in these systems is irreversible, by Mokrousov G. M [3] for preservation of
possibility of applying this M. Pourbaix approach and representation of result in the form of the
Eeq − pH diagrams was represented the hypothesis on the existence of quasi equilibrium at the
interphase boundaries and its adequacy to the steady state condition [3]. For the account of the shift
of equilibrium with respect to the component B to the cathode direction in comparison with the value
of Eeq in the GaAs−H2O system he was offered to introduce a correction for reversibility into the
potential-determining reaction of uniform (pseudoselective) destruction of compound, taking into
account the solubility of arsenic oxide as y, and part of the soluble form of electropositive element B
(0) precipitated from the solution, as х. This approach allow us to consider the processes using the
thermodynamic representations – the potential-determining reactions within the framework of the
quasi equilibrium calculated electrode potential ( Eeqq ) − рН dependences. In this approach is used
the general principles of the description of the possible dissolution (oxidation, destruction)
mechanisms of intermetallic compounds and solid solution, developed in [14].
For the solution of a question of nature of interphase transformations in the multicomponent
substance − Н2O (рН) system, all possible reactions, taking into account the redox states of elements
of substance, and mechanisms of dissolution/oxidation of substance depending on рН are
considered; the values of the Gibbs energy (∆G) and corresponding values of quasi equilibrium
calculated electrode potentials are calculated. Then, the Eeqq −рН diagrams for the compound − Н2O
(рН) systems are plotted. The possible mechanisms of multicomponent solids destruction are their
uniform and selective dissolution or oxidation of the electronegative component (for III-V
compounds, this is the element of the third group), and also pseudoselective destruction (a uniform
dissolution followed by separation the more electropositive component (an element of the fifth
group) from the solution) with the proportion of х.
In the general case, for III-V arsenides and antimonides, on the basis of the mechanism of their
destruction (dissolution, oxidations), it is possible to select the following set of reactions.
The uniform dissolution (oxidation):
A3+, AOH2++BO+, HBO2+xH++6e=AB+yH2O;
+HBO2,
+xH++6e=AB+yH2O;
A2O3, 2A(OH)3+B2O3 +xH++12e=2AB+yH2O;
2A3+, 2AOH2++B2O3+xH++12e=2AB+yH2O;
A2O3, 2A(OH)3+2HBO2, 2
+xH++12e=2AB+yH2O;
A3+, AOH2+, AO2–+
,
+xH++8e=AB+yH2O.
©Бутлеровские сообщения. 2011. Т.24. №3. _________________ E-mail: [email protected] ____________ 63
Full-text research publication __________________
Mokrousov G. M., Zarubina O. N., and Bekezina T. P.,
and Naiden E.P.
The selective (pseudoselective) destruction:
A3+, AOH2+,
+B+xH++3e=AB+yH2O;
AB+3H++3e=A+BH3(g.);
A2O, A2O3, 2A(OH)3+2B+xH++4(6)e=2AB+yH2O.
In the simplified version the Eeqq − рН diagrams for the H2O−InAs and H2O−GaAs systems
with description of typical reactions and stable forms of substances are presented in [15]. The similar
diagram for indium antimonide is described in [3].
The values of Eeqq lie between the values of Eeq of the V and III group components: EeqA
< Eeqq < EeqB. In this regard, at the surface of compound, equilibrium with respect to the component A
is shifted to the anode region, and equilibrium with respect to the component B – to the cathode
region; the former should is irreversible to be oxidized/dissolved, and the later either not to
participate in reaction at all, or after dissolution, in accordance with the mechanism of the
pseudoselective destruction of substance, to precipitate on the surface in the form of element хB (0).
If define the basic set of possible potential-determining reactions with allowance for solubility of
oxide of an element of the fifth group as y and for shift of equilibrium of the soluble form of an
element B to the cathode region as х, can receive the total compromise equations of potentialdetermining reactions of pseudoselective destruction of compounds. Such equations for indium
arsenide and gallium arsenide are presented in [15].
Using the Eeqq − рН diagrams, on the basis of corresponding potential-determining reactions
and experimentally measured values of stationary potential, we can estimate the possible
composition of the phase surface layer, formed at the surface of compound under certain values of
pH at an establishment of a steady state or in conditions of shift of the electrode potential to the
anode or cathode region.
An important consequence of the phenomena, occurring at the interphase boundary (surface)
of the multicomponent compounds, is the change of their stoichiometric ratio as a result of selective
or pseudoselective destruction. In turn, it should lead to formation in a part of the crystal layer,
adjoining to the superficial phase layer (or solution), of lattice vacancies of the electronegative
component (VА) and to antisite defects of type «an element of the fifth group on-site of an element of
the third group» (ВА). On achieving the limits of homogeneity (~1019 at./sm3 for III-V
semiconductors) in such near-surface crystal layers may occur a decay of the near-surface region
supersaturated by lattice vacancies with the formation of phase of the electropositive component
B(0). This process is localized at the interface between the volume of crystalline substance and the
superficial phase layer or, in the absence of last, between the volume of crystalline substance and the
aqueous medium. We call this boundary the near-surface layer. It represents the near-surface region
of crystalline substance with the destroyed stoichiometry. By the example of indium arsenide the
possible variants of composition and structure of surface, formed in strongly acidic (рН <-1-0) and
alkaline (рН >11-13) mediums in region of selective (pseudoselective) and uniform destruction of
compound, are presented, accordingly, on fig. 1,a and 1,b. The surface represents the two-layer
structure consisting from the near-surface crystal layer of the semiconductor with changed
stoichiometric ratio and the superficial phase layer of the element of the fifth group; in the surface
layer there are no oxidized forms of components A and B. As the rate of dissolution of InAs is
determined by the activity of arsenic, and the latter in comparison with indium is more slowly leaves
the surface and under the uniform destruction of compound in the crystal lattice of the
semiconductor can expect the formation of indium vacancies and antisite defects (fig. 1b). The
superficial phase layer in this case should not be formed.
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As
PHYSICAL CHEMISTRY OF PROCESSES AT THE MULTICOMPONENT SUBSTANCE-SOLUTION…– ___ 61-69
x
x
InAs
InAs
InAs
As
InAs
а
b
AsIn
VIn ,
As,
In ,
Figure. 1. Schemes of the surface structure on InAs, constructed by results of calculations of quasi
equilibrium under conditions of pseudoselective or selective (a) and uniform (b) destruction of
compound for the InAs-H2O system (рН < –10 and рН ≥ 1113).
Results of studies by The X-ray photoelectron spectroscopy of the gallium arsenide surface
after the treatments in acid and alkali solutions show that almost full gallium depletion of the surface
occurs in units of seconds [16]. These results do not only correspond to the received conclusion that
the surface is depleted of the more electronegative component in a steady state equilibrium, but also
confirm that dissolution (oxidation) of multicomponent compounds is accompanied by selective
output of electronegative component A from the near-surface region of semiconductor. The similar
picture will be observed and for antimonides. The diagram of phase equilibrium Eeq – рН for
antimony is similar to the diagram for arsenic [15], but the solubility of antimony oxide is
approximately on two orders is lower than solubility of arsenic oxide, and the antimony oxide has
also the broad band of existence in рН. Therefore for antimonides in steady state conditions the
reactions of selective and pseudoselective destruction are more characteristic.
Thus, in the conditions of quasi (steady state) equilibrium on the interphase boundary (reaction
zone) the constant drain of electronegative component in solution or in a superficial phase layer can
be observed. In connection with this, the ratio of components of the compound can reach a limiting
deviation value from stoichiometry. In case of considered by us III-V compounds, this value usually
does not exceed ~1019 at/sm3 [17, 18]. Accordingly, in the near-surface layer the high value of the
concentration gradient can be reached: from ~1019 at/sm3 to ~1022 at/sm3 (the average density of
atoms in a solid). It follows from this that the formation of the near-surface layer is determined by
the chemical activity and concentration gradient of components at the interphase boundary, and first
of all, by the diffusion of atoms of electronegative component (indium) from the bulk. The nearsurface layer is formed under the diffusion control. For the calculation of its size it is necessary to
use not thermodynamic, but the kinetic approach. The higher the diffusion coefficient of the
electronegative component from the bulk of semiconductor and the lower the overall rate of its
destruction, the greater the size of emerging depleted diffusion (reaction) zone.
Consider the change in the concentration of atoms normally to the surface (the method of
semi-infinite diffusion). The case can be solved by applying Fick's second law for the unsteady-state
diffusion (the concentration depends on the distance and time):
C λ, t 
 2C λ, t 
D
t
λ 2
where С is the concentration; t is the time; λ is the thickness of the diffusion (near-surface)
layer; D is the diffusion coefficient of atoms A.
After using the Laplace transform, the equation takes the form:
C λ, t   C0 1  erf Z 
(1)
where
Z
λ
2 D t
(2)
©Бутлеровские сообщения. 2011. Т.24. №3. _________________ E-mail: [email protected] ____________ 65
Full-text research publication __________________
Mokrousov G. M., Zarubina O. N., and Bekezina T. P.,
and Naiden E.P.
С0 is the concentration of atoms in the bulk of the crystal (1022 cm–3).
The diffusion coefficient D depends on the concentration of vacancies, temperature, and other
parameters. Its value in the near-surface layer is unknown; it can be expected that the values of D lie
in the range from 10–12 cm2/s (as in the bulk of the crystal) to 10–6 cm2/s (as in solution). From
equation (1), can find the value of Zmax, at which С(λ,t) =1·1019 cm–3. Zmax = 2.326. Substituting in
(2) the values of the time for various D, (range from 1·10-12 to 1·10-6 sm2/s), with taking into account
Zmax, we obtain a matrix of values of λ (table).
Table. The thickness of the near-surface layer λ for given values of the
diffusion coefficient D and time t
Time, s
–4
1·10
3·10–4
7·10–4
1·10–3
3·10–3
7·10–3
1·10–2
3·10–2
7·10–2
1·10–1
–12
1·10
4.65·10–8
8.06·10–8
1.23·10–7
1.47·10–7
2.55·10–7
3.89·10–7
4.65·10–7
8.06·10–7
1.23·10–6
1.47·10–6
λ (cm) for different values of the diffusion coefficients (cm2/s)
1·10–11
1·10–10
1·10–9
1·10–8
1·10–7
–7
–7
–6
–6
1.47·10
4.65·10
1.47·10
4.65·10
1.47·10–5
–7
–7
–6
–6
2.55·10
8.06·10
2.55·10
8.06·10
2.55·10–5
–7
–6
–6
–5
3.89·10
1.23·10
3.89·10
1.23·10
3.89·10–5
–7
–6
–6
–5
4.65·10
1.47·10
4.65·10
1.47·10
4.65·10–5
–7
–6
–6
–5
8.06·10
2.55·10
8.06·10
2.55·10
8.06·10–5
1.23·10–6
3.89·10–6
1.23·10–5
3.89·10–5
1.23·10–4
1.47·10–6
4.65·10–6
1.47·10–5
4.65·10–5
1.47·10–4
–6
–6
–5
–5
2.55·10
8.06·10
2.55·10
8.06·10
2.55·10–4
–6
–5
–5
–4
3.89·10
1.23·10
3.89·10
1.23·10
3.89·10–4
–6
–5
–5
–4
4.65·10
1.47·10
4.65·10
1.47·10
4.65·10–4
1·10–6
4.65·10–5
8.06·10–5
1.23·10–4
1.47·10–4
2.55·10–4
3.89·10–4
4.65·10–4
8.06·10–4
1.23·10–3
1.47·10–3
We can expect that because of large number of vacancies, the value of diffusion coefficient in
the near-surface region of the crystal can increase by several orders of magnitude in comparison with
it in the bulk of the crystal. At the same time, it cannot reach the values of D, characteristic of the
solution. Therefore, in the matrix it is possible to distinguish the area of the most probable values of
λ if neglect the extreme values of diffusion coefficient. Taking into account that the equilibrium of
the diffusion process can be reached in a time from 1·10-4 to 1·10-2 s [18], we obtain the range of
allowable values of λ = [5·10-7; 5·10-5] cm. Thus, the thickness of the near-surface crystal layer with
destroyed stoichiometric ratio (depleted by the component A) may lie in the range from 5 to 500 nm.
The calculations did not take into account the possible reconstruction of the near-surface layer of the
crystal with the formation of new two-dimensional phases.
Experiment
The investigation is carried out on InSb (221) monocrystals. Before studying, the surface of the wafers
was mechanically polished by aluminium oxide powder (diameter of particles is 300 nm), degreased in
boiling toluene, and polished in the etchant of 20% tartaric acid, 33% H2O2, 49% HF in the ratio 59:39:2 at
room temperature.
Structural parameters of indium antimonide after the liquid chemical treatments were investigated by
X-ray diffraction with an X-ray diffractometer Shimadzu XRD 6000. Qualitative determination of phase
composition of the surface of indium antimonide was performed by contact voltammetry directly from a
surface of wafers with an electrochemical cell with a slung working electrode; the investigated wafer was
used as a working electrode. For identification of current-voltage peaks, the data of phase electrochemical
transformations on the surface of InSb [19] were used. The values of potentials are measured against the
saturated silver chloride electrode. As a subsidiary electrode, a platinum wire was used. As the base
electrolyte, 0.03 M solution of hydrochloric acid was applied. The current-voltage relationships were
registered in a differential form with using the universal polarograph PU-1 with an interface block "Graphite 2".
As a selective etchant, an aqueous solution of chromic anhydride and hydrofluoric acid of variable
composition was used; etching time was 60 seconds at room temperature. As a uniform etchant was used a
solution of hydrochloric acid (pH=1) at room temperature with the anodic polarization. To remove the
damaged layer of the semiconductor and to reduce the natural oxide layer, treatment of wafers in a polishing
etchant was carried out (the composition is described above).
Results and their discussion
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PHYSICAL CHEMISTRY OF PROCESSES AT THE MULTICOMPONENT SUBSTANCE-SOLUTION…– ___ 61-69
After the uniform etching in a solution of hydrochloric acid (pH = 1) with the anodic
polarization on the surface of indium antimonide by voltammetry was found a significantly decrease
of the relative intensity of phase peaks of elementary antimony (fig. 2, curve 2) as compared with the
original surface (fig. 2, curve 1). In consequence of the selective etching there is an accumulation of
elementary antimony (fig. 2, a curve 3). The character of observable dependence of a component of
the fifth group completely corresponds to the expected (calculated) dependence.
Figure. 2. Differential anodic current-voltage dependences for initial
surfaces of InSb (1), after the uniform etching (2), and after the selective etching (3)
X-ray analysis of samples after the uniform etching showed a slight accumulation of
antimony; no destruction of the crystal structure in the superficial region of the semiconductor was
found (fig. 3). After the selective etching, the concentration of antimony in the surface layer
increased. Nanosized inclusions of elementary antimony are found; the near-surface layer of the
semiconductor has the destroyed crystal structure (fig. 4). Thus, the character of observable
dependence on phase structure of surface layer and the presence of the near-surface layer with the
destroyed crystal structure completely corresponds to expected (calculated) layer.
Figure. 3. X-ray diffraction spectrum of InSb after the uniform etching
©Бутлеровские сообщения. 2011. Т.24. №3. _________________ E-mail: [email protected] ____________ 67
Full-text research publication __________________
Mokrousov G. M., Zarubina O. N., and Bekezina T. P.,
and Naiden E.P.
Figure. 4. X-ray diffraction spectrum of InSb after the selective etching
Сonclusion
Thus, on the basis of the hypothesis of the existence of quasi equilibrium at the boundary
multicomponent compound – water (рН) with using the thermodynamic and kinetic representations
is confirmed that the surface of compounds represents the structure consisting from the superficial
phase layer and the near-surface crystal layer with the destroyed stoichiometry.
The phase structure of the superficial layer can be predicted and set with the quasi equilibrium
diagrams of type of Pourbaix. It is carried out by selection of potential-determining reactions with
the value of calculated potential close to the experimental measured (or set by means of external
electric field) value of electrode potential under certain values of рН of the solution.
The composition of the near-surface crystal layer formed between the volume of the
semiconductor and superficial phase layer (or, in the absence of the last, solution), is caused by
change in the stoichiometry because of the non-uniform destruction of the compounds proceeding
with a primary exit of the electronegative component into the solution (or oxide/hydroxide). Its
presence proves to be true the results of X-ray analysis. It is shown that under the selective and
pseudoselective destruction of the III-V compounds, the thickness of the near-surface layer depleted
of the electronegative component can range from 5 to 500 nm.
Acknowledgements
The work was performed with support of the Russian Foundation for Basic Research (project
№ 10-08-00575).
References
[1] Gibbs J.V. Thermodynamics. Statistical Mechanics [in Russian], Nauka, Moscow (1982).
[2] Oura K., Lifshits V.G., Saranin А.А., et al., Introduction to the Physics of Surface [in Russian], Nauka,
Moscow (2006).
[3] Mokrousov G.M., Reconstruction of Solids at the Interfaces [in Russian], Izd. Tomsk. Univers., Tomsk
(1990).
[4] Brudnyi V.N., Grinyaev S.N., Kolin N.G. A model for Fermi-level pinning in semiconductors: radiation
defects, interface boundaries. Physica B. 2004. Vol.348. P.213-225.
[5] Robertson J. Interface states model for III-V oxide interfaces. Microelectron. Eng. 2009. Vol.86. P.15581560.
[6] Price J., Barnett J., Raghavan S., Keswani M., Govingarajan R. A study of the interaction of gallium
arsenide with wet chemical formulations using thermodynamic calculations and spectroscopic
ellipsometry. Microelectron. Eng. 2010. Vol.87. No.9. P.1661-1664.
68 ______________ http://butlerov.com/ _______________ ©Butlerov Communications. 2011. Vol.24. No.3. P.61-69.
PHYSICAL CHEMISTRY OF PROCESSES AT THE MULTICOMPONENT SUBSTANCE-SOLUTION…– ___ 61-69
[7] Quagliano L.G. Detection of As2O3 arsenic oxide on GaAs surface by Raman scattering. Appl. Surface
Sci. 2000. Vol.153. P.240-244.
[8] Dmitruk N., Kutovyi S., Dmitruk I., Simkiene I., Sabataityte J., Berezovska N. Morphology, Raman
scattering and photoluminescence of porous GaAs layers. Sensors and Actuators. 2007. Vol.B126. P.294300.
[9] Pourbaix M. Atlas of electrochemical equilibria in aqueous solution. N.Y.: Pergamon Press. 1966. 644p.
[10] Damaskin B., Petriy O. Electrochemistry [in Russian], Vyssh. Shk., Moscow (1987).
[11] Latimer V.М, Oxidation States of Elements and their Potentials in Aqueous Solutions [in Russian
translation], IL, Moscow (1954).
[12]
Batenkov V. A, Kataev G.A. Gallium arsenide. Izd. Tomsk. Univers. 1969. Vol.2. P.220-224.
[13] Schwartz B. GaAs surface chemistry – a review. CRC Crit. Revs. Solid State Sci. 1975. Vol.5. No.4.
P.609-624.
[14] Marshakov I.K. Corrosion and anticorrosion protection: Summary of science and engineering [in Russian
translation], VINITI, Moskow. 1971. Vol.1. P.138-155.
[15] Zarubina O.N., Mokrousov G.M., Butlerov Communications. 2009. V.17. No.6. P.33-40.
[16] Nemoshkalenko V.V., Aleshin V.G.,Gassanov L.G., et al., Poverkhn. Fiz. Khim., Mekhan., 1983. №2.
P.88-94.
[17] Mil,vidskii M.G., Osvenskii V.B., Structural Defects in Single Crystals of Semiconductors [in Russian],
Metallurg., Moscow (1984).
[18] Van de Ven J., Weyher J.L.. Kinetics and morphology of GaAs etching in aqueous CrO3HF solutions.
J. Electrochem. Soc. 1986. Vol.133. No.4. P.799-806.
[19] Boltaks B.I., Diffusion and Point Defects in Semiconductors, Nauka, Leningrad (1972).
[20] Smirnova T.P., Shpurik V.N., Belyy V.I., Zakharchuk N.F. Izv. SO AN SSSR, Ser. Chemical. 1982. №7.
Issue 3. P.93-97.
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