Multicomponent chalcogenide-contained films are appeared as an interesting nonequilibrium thermodynamic system. Structural and electric field-induced characteristics of these materials are not investigated. The paper reports for the first time experimental data on growth, morphology and electrophysical properties of NaBiTe2 thin films. The investigated samples were condensed on glass substrates under deposition rate 0.1-0.5
nm/s at T = 300 K and vacuum level P = 10-3 Pa. Metal-semiconductor (MS) Cr/NaBiTe2 structures were prepared for electrical studies. Room-temperature time dependence of the current flowing through the investigated structure under applied
electric field is also discussed.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2054

Bilozertseva, V.I.

Dyakonenko, N.I.

Gaman, D.A.

Khlyap, H.M.

Mamalui, A.A.

Petrenko, L.G.

Electronic Sumy State University Institutional Repository

280                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II              NANOSTRUCTURED NaBiTe2 THIN FILMS AND  THEIR PROPERTIES Violetta I. Bilozertseva1*, Dmitriy A. Gaman 1, Halyna M. Khlyap 2,  Andrey A. Mamalui 1, Nina L. Dyakonenko 1, Lina G. Petrenko 1   1  National Technical University "Kharkov Polytechnical Institute", 21 Frunze str., Kharkov, 61002 Ukraine 2 University of Technology, Distelstr.11, D-67657 Kaiserslautern, Germany  ABSTRACT Multicomponent chalcogenide-contained films are appeared as an interesting non-equilibrium thermodynamic system. Structural and electric field-induced characteristics of these materials are not investigated. The paper reports for the first time experimental data on growth, morphology and electrophysical properties of NaBiTe2 thin films. The investigated samples were condensed on glass substrates under deposition rate 0.1-0.5 nm/s  at  T  =  300  K  and  vacuum  level  P  =  10-3 Pa. Metal-semiconductor (MS) Cr/NaBiTe2 structures were prepared for electrical studies. Room-temperature time dependence of the current flowing through the investigated structure under applied electric field is also discussed.   Keywords: films, chalcogenide, NaBiTe2, surface relief, electric properties.  INTRODUCTION The amorphous films of complex ternary chalcogenide compounds are characterized by a wide range of physical and chemical properties. Neverthe-less, different investigations of such materials were rarely carried out without using an opportunity to obtain systematic information about the subject of the study. Two main factors should be noted: i) only relatively small number of chalcogenide materials may be evaporated producing a stoichiometric film. The deviations from stoichiometry observed experimentally led to sufficient chang-es of necessary characteristic of the sample; ii) self-organization processes which are typical for complex multicomponent systems cause the various phase transitions leading to oxidation, amorphous phase crystallization, time evolu-tion of stoichiometry, etc [1]. As it is known, crossing from elementary Group IV crystal semiconductor Ge  and  Si  to  similar  binary  compounds  AIIIBV (A  =  Ga,  In,  B  =  As,  Sb,  Bi)  brings more complex crystal structure and ionic component of the chemical bonds due to appearance of two sorts of ordered atoms. Further complication of chemical composition in ternary compounds causes change of atoms in the                                                * e-mail: biloz@mail.ru Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II              281  cation sublattice resulting in new physical properties. Therefore, their structur-al, optical and electric properties attract special interest of researchers working in field of nanotechnology and nanoelectronic applications [2-4]. The paper describes for the first time experimental results on growth and electric field-induced characteristics of thin films prepared from NaBiTe2 chal-cogenide semiconductor. This compound crystallizes in NaCl-like cubic lattice with parameter a=0,639 nm. STRUCTURAL INVESTIGATIONS The microstructure and phase composition of the films have been studied by transmission electron microscopy (TEM) and diffraction methods. Two sets of films were selected for structural studies: the first family of as-grown layers (glass substrate, Ts= 300K) and the second group of specimens deposited on the glass substrate at the room temperature after annealing in air under normal atmospheric conditions. As it  is shown in Fig.1, the film microstructure is characterized by pres-ence of small disperse particles. The amorphous and microcrystalline phases are good seen in the electron-diffraction patterns. The electron beam-induced anneal leads to the film crystallization and re-evaporation of tellurium. After annealing in air under normal atmospheric conditions at T = 373 – 393 K nano-crystals Bi2Te3 and NaTe3 as well as nanoparticles are observed (see Fig.2).    Fig. 1 – TEM image, diffraction and microdiffraction patterns of the NaBiTe2 films with 30 nm thickness deposited on the glass substrate at Ts = 300K under deposition rate 0.1 nm/s (the original sample) Fig. 2 – TEM image, diffraction and mi-crodiffraction patterns of the NaBiTe2 films with 80 nm thickness deposited to the glass substrate at Ts = 300K under deposi-tion rate 0.5 nm/s after annealing in air under normal atmospheric conditions  282                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II              The heat treatment of the films in air is accompanied by the formation of BiO3 and TeO2 oxides. RESULTS OF ELECTRICAL MEASUREMENTS. Studies of the electric field-induced properties were carried out in vacuum (in the growth chamber in situ) as well as in open air at normal atmospheric conditions and under applied electric field up to 104 V/m. The current-voltage characteristic of the film is illustrated by the Fig.3.  As it is shown, this dependence is of exponential character typical for metal-semiconductor structures. Such a characteristic may be qualitatively described as follows:  j(Fa) ~ j0exp[(eFadtun+ ')/kBT] (1) where Fa is the applied electric field, dtun is the distinctive tunneling length,  ' is the tunneling parameter defined numerically, and j0 stands for a saturation current [5]. Fore more detailed study of current mechanisms in the investigated structure the experimental curve was re-built in semi-log and double log scales (Fig.4 a, b). Double-log recalculation of the experimental current-voltage dependence shows the smooth superposition of at least three modes of the carri-ers transport: i) current caused by the carriers injected from the metallic contact  under the applied voltage 50-100 V [6];  ii) velocity-saturation regime under the applied voltage up to 120 V, where  I~(2İİ0vsatVa/L2) (2)  vsat is determined from the experimental data and L is the thickness of the film;  iii) The current governed by so-called “3/2”-law as the applied voltage in-creases:   I~(4 İİ0/9L2)(2e/m*)1/2(Va)3/2 (3)   Fig. 3 – Room-temperature current-field charac-teristic of the investigated sample (Cr-contacts) Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II              283    a b Fig. 4 – Semi log current-field characteristic of the investigated  sample (Cr-contacts) (a) and Double-log current-field characteristic of the investigated sample (Cr-contacts) (b)  CONCLUSIONS. The structural characteristics and electric field-induced properties of met-al-semiconductor structure Cr/NaBiTe2 are investigated for the first time. Room-temperature current-voltage characteristics revealed a smooth superposi-tion of drift-diffusion current, velocity saturation mode and ballistic regime at the all range of applied voltage (0-140 V).  The phase transition amorphous state – crystal state in the films under study does not lead to the significant changes of their characteristics.   Acknowledgements Authors  are  grateful  to  Dr.  S.N.  Grigorov  for  technical  help  and  to  Dr.  V.I. Perekrestov for useful discussions. REFERENCES [1] Electronic processes on the semiconductor surface under chemisorptions. (F.F. Volkenstein), Nauka Publishers, Moscow, 1987. [2] M. Takahashi, M. Kojima, S. Sato, N. Ohnisi, J. Appl. Phys. 2004, Vol.96, P. 5582-5587. [3] V Bilozertseva, V Bazakutsa, S Gapochenko et al. Optical properties and photo-induced effects in Ge-As-Se films and two-layer systems on their basis. SPIE 2003, Vol. 5024, P. 80-84. [4] M. Ulrich, A. Bunde, C. Kohl , D. Appl. Phys. Lett., 2004, Vol. 85, P. 242-244. [5] Ng. Kwok, Guide to Semiconductor Devices, Wiley, New York, 2002. [6] B. Braunecker, D. Feldman and J. Marston, Phys. Rev., 2005, Vol. B72, P. 125311-125318.   

Nanostructured NaBiTe2 thin films and their properties

SocioEconomic Challenges Journal (Sumy State University)

280                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II             
 
NANOSTRUCTURED NaBiTe2 THIN FILMS AND  
THEIR PROPERTIES 
Violetta I. Bilozertseva1*, Dmitriy A. Gaman 1, Halyna M. Khlyap 2,  
Andrey A. Mamalui 1, Nina L. Dyakonenko 1, Lina G. Petrenko 1  
 
1  National Technical University "Kharkov Polytechnical Institute", 21 Frunze str., Kharkov, 61002 
Ukraine 
2 University of Technology, Distelstr.11, D-67657 Kaiserslautern, Germany 
 
ABSTRACT 
Multicomponent chalcogenide-contained films are appeared as an interesting non-
equilibrium thermodynamic system. Structural and electric field-induced characteristics 
of these materials are not investigated. The paper reports for the first time experimental 
data on growth, morphology and electrophysical properties of NaBiTe2 thin films. The 
investigated samples were condensed on glass substrates under deposition rate 0.1-0.5 
nm/s  at  T  =  300  K  and  vacuum  level  P  =  10-3 Pa. Metal-semiconductor (MS) 
Cr/NaBiTe2 structures were prepared for electrical studies. Room-temperature time 
dependence of the current flowing through the investigated structure under applied 
electric field is also discussed.  
 
Keywords: films, chalcogenide, NaBiTe2, surface relief, electric properties. 
 
INTRODUCTION 
The amorphous films of complex ternary chalcogenide compounds are 
characterized by a wide range of physical and chemical properties. Neverthe-
less, different investigations of such materials were rarely carried out without 
using an opportunity to obtain systematic information about the subject of the 
study. Two main factors should be noted: i) only relatively small number of 
chalcogenide materials may be evaporated producing a stoichiometric film. The 
deviations from stoichiometry observed experimentally led to sufficient chang-
es of necessary characteristic of the sample; ii) self-organization processes 
which are typical for complex multicomponent systems cause the various phase 
transitions leading to oxidation, amorphous phase crystallization, time evolu-
tion of stoichiometry, etc [1]. 
As it is known, crossing from elementary Group IV crystal semiconductor 
Ge  and  Si  to  similar  binary  compounds  AIIIBV (A  =  Ga,  In,  B  =  As,  Sb,  Bi)  
brings more complex crystal structure and ionic component of the chemical 
bonds due to appearance of two sorts of ordered atoms. Further complication of 
chemical composition in ternary compounds causes change of atoms in the 
                                               
* e-mail: biloz@mail.ru 
Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II              281 
 
cation sublattice resulting in new physical properties. Therefore, their structur-
al, optical and electric properties attract special interest of researchers working 
in field of nanotechnology and nanoelectronic applications [2-4]. 
The paper describes for the first time experimental results on growth and 
electric field-induced characteristics of thin films prepared from NaBiTe2 chal-
cogenide semiconductor. This compound crystallizes in NaCl-like cubic lattice 
with parameter a=0,639 nm. 
STRUCTURAL INVESTIGATIONS 
The microstructure and phase composition of the films have been studied 
by transmission electron microscopy (TEM) and diffraction methods. 
Two sets of films were selected for structural studies: the first family of 
as-grown layers (glass substrate, Ts= 300K) and the second group of specimens 
deposited on the glass substrate at the room temperature after annealing in air 
under normal atmospheric conditions. 
As it  is shown in Fig.1, the film microstructure is characterized by pres-
ence of small disperse particles. The amorphous and microcrystalline phases 
are good seen in the electron-diffraction patterns. The electron beam-induced 
anneal leads to the film crystallization and re-evaporation of tellurium. After 
annealing in air under normal atmospheric conditions at T = 373 – 393 K nano-
crystals Bi2Te3 and NaTe3 as well as nanoparticles are observed (see Fig.2). 
 
  
Fig. 1 – TEM image, diffraction and 
microdiffraction patterns of the NaBiTe2 
films with 30 nm thickness deposited on 
the glass substrate at Ts = 300K under 
deposition rate 0.1 nm/s (the original 
sample) 
Fig. 2 – TEM image, diffraction and mi-
crodiffraction patterns of the NaBiTe2 
films with 80 nm thickness deposited to the 
glass substrate at Ts = 300K under deposi-
tion rate 0.5 nm/s after annealing in air 
under normal atmospheric conditions 
 
282                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II             
 
The heat treatment of the films in air is accompanied by the formation of 
BiO3 and TeO2 oxides. 
RESULTS OF ELECTRICAL MEASUREMENTS. 
Studies of the electric field-induced properties were carried out in vacuum 
(in the growth chamber in situ) as well as in open air at normal atmospheric 
conditions and under applied electric field up to 104 V/m. 
The current-voltage characteristic of the film is illustrated by the Fig.3.  
As it is shown, this dependence is of exponential character typical for 
metal-semiconductor structures. Such a characteristic may be qualitatively 
described as follows: 
 j(Fa) ~ j0exp[(eFadtun+ ')/kBT] (1) 
where Fa is the applied electric field, dtun is the distinctive tunneling 
length,  ' is the tunneling parameter defined numerically, and j0 stands for a 
saturation current [5]. 
Fore more detailed study 
of current mechanisms in the 
investigated structure the 
experimental curve was re-
built in semi-log and double 
log scales (Fig.4 a, b). 
Double-log recalculation 
of the experimental current-
voltage dependence shows the 
smooth superposition of at 
least three modes of the carri-
ers transport: 
i) current caused by 
the carriers injected from the 
metallic contact  under the 
applied voltage 50-100 V [6];  
ii) velocity-saturation regime under the applied voltage up to 120 V, 
where 
 I~(2İİ0vsatVa/L2) (2) 
 
vsat is determined from the experimental data and L is the thickness of the 
film;  
iii) The current governed by so-called “3/2”-law as the applied voltage in-
creases:  
 I~(4 İİ0/9L2)(2e/m*)1/2(Va)3/2 (3) 
 
 
Fig. 3 – Room-temperature current-field charac-
teristic of the investigated sample (Cr-contacts) 
Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II              283 
 
  
a b 
Fig. 4 – Semi log current-field characteristic of the investigated  sample (Cr-
contacts) (a) and Double-log current-field characteristic of the investigated 
sample (Cr-contacts) (b) 
 
CONCLUSIONS. 
The structural characteristics and electric field-induced properties of met-
al-semiconductor structure Cr/NaBiTe2 are investigated for the first time. 
Room-temperature current-voltage characteristics revealed a smooth superposi-
tion of drift-diffusion current, velocity saturation mode and ballistic regime at 
the all range of applied voltage (0-140 V).  The phase transition amorphous 
state – crystal state in the films under study does not lead to the significant 
changes of their characteristics.  
 
Acknowledgements 
Authors  are  grateful  to  Dr.  S.N.  Grigorov  for  technical  help  and  to  Dr.  
V.I. Perekrestov for useful discussions. 
REFERENCES 
[1] Electronic processes on the semiconductor surface under chemisorptions. 
(F.F. Volkenstein), Nauka Publishers, Moscow, 1987. 
[2] M. Takahashi, M. Kojima, S. Sato, N. Ohnisi, J. Appl. Phys. 2004, Vol.96, P. 5582-
5587. 
[3] V Bilozertseva, V Bazakutsa, S Gapochenko et al. Optical properties and photo-
induced effects in Ge-As-Se films and two-layer systems on their basis. SPIE 2003, 
Vol. 5024, P. 80-84. 
[4] M. Ulrich, A. Bunde, C. Kohl , D. Appl. Phys. Lett., 2004, Vol. 85, P. 242-244. 
[5] Ng. Kwok, Guide to Semiconductor Devices, Wiley, New York, 2002. 
[6] B. Braunecker, D. Feldman and J. Marston, Phys. Rev., 2005, Vol. B72, P. 125311-
125318. 
  


The paper reports our experimental data on growth, morphology, optical and electrophysical properties
of NaBiTe2 thin films grown by thermal evaporation in vacuum. The structural characteristics and electric
field-induced properties of semiconductor NaBiTe2 films with Cr contacts are investigated. Roomtemperature
time dependence of the current flowing through the investigated structures under applied
electric field is also discussed. The influence of some aggressive atmospheric impurities on NaBiTe2 films
characteristics is described for the first time.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2492

Dyakonenko, N.L.

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ Vol. 4 No 1, 01019(5pp) (2012) Том 4 № 1, 01019(5cc) (2012)   2077-6772/2012/4(1)01019(5) 01019-1  2012 Sumy State University Nanostructured NaBiTe2 Thin Films and Their Properties  V.I. Bilozertseva1,*, D.A. Gaman1, H.M. Khlyap2, A.A. Mamalui1, N.L. Dyakonenko1, L.G. Petrenko1  1 National Technical University "Kharkov Polytechnical Institute", 21 Frunze str., Kharkov, 61002 Ukraine 2 University of Technology, Distel str. 11, D-67657 Kaiserslautern, Germany  (Received 06 November 2011; published online 14 March 2012)  The paper reports our experimental data on growth, morphology, optical and electrophysical properties of NaBiTe2 thin films grown by thermal evaporation in vacuum. The structural characteristics and electric field-induced properties of semiconductor NaBiTe2 films with Cr contacts are investigated. Room-temperature time dependence of the current flowing through the investigated structures under applied electric field is also discussed. The influence of some aggressive atmospheric impurities on NaBiTe2 films characteristics is described for the first time.  Keywords: Thin films, Chalcogenide, NaBiTe2, Structure, Surface relief, Optical transmission, Electric properties, Current mechanisms, Gas sensitivity.   PACS numbers: 68.55.ag, 72.80.Jc   ______________ * biloz@mail.ru  1. INTRODUCTION  Thin films of complex ternary chalcogenide com-pounds are characterized by a wide range of physical and chemical properties. Nevertheless, the various in-vestigations of such materials were rarely carried out with using an opportunity to obtain systematic infor-mation about the subject of the study. Two main factors should be noted: i) only relatively small number of chalcogenide materials may be evaporated producing a stoichiometric film. The deviations from stoichiometry observed experimentally led to sufficient changes of necessary characteristic of the sample; ii) self-organization processes which are typical for complex multicomponent systems cause the phase transitions leading to oxidation, amorphous phase crystallization, time evolution of stoichiometry, etc. [1]. As it is known, crossing from elementary Group IV crystal semiconductor Ge and Si to similar binary com-pounds AIIIBV (A = Ga, In, B = As, Sb, Bi) brings more complex crystal structures and ionic components of the chemical bonds due to appearance of two sorts of or-dered atoms. Further complication of chemical compo-sition in ternary compounds causes change of atoms in the cation sublattice resulting in new physical proper-ties. Therefore, their structural, optical and electric properties attract special interest of researchers work-ing in field of nanotechnology and nanoelectronic appli-cations [2-4]. Earlier we have studied electric field-induced char-acteristics of NaSbSe2 [5]. The presence of chalcogene element makes it possi-ble to affect the stability and sensitivity to ambient environment of the respective thin films creating a per-spective for using them as active elements of sensor devices [6]. The paper describes experimental results on growth, structure, optical and electric field-induced characteris-tics of thin films prepared from NaBiTe2 chalcogenide semiconductor. This compound crystallizes in NaCl-like cubic lattice with parameter a = 0,639 nm.  2. EXPERIMENTAL  NaBiTe2 thin films with different thicknesses (60 – 200 nm) were deposited on glass substrates from Knudsen cell under vacuum level P = 10–3 Pa. The av-erage rate of deposition was operated by change of the evaporator temperature and estimated to be 0.1 – 0.5 nm/s. The area of the samples was measured to be 6  32mm2, the distance between electrodes had not exceeded 30 mm.  The microstructure and phase composition of the films have been studied by transmission electron mi-croscopy (TEM) and diffraction methods. AFM investigations of as-grown samples and after NO exposition were carried out. Two sets of NaBiTe2 samples were prepared: with Cr contacts for electric studies and without them for optical investigations. To provide maximum accuracy of the electric measurements focusing on NaBiTe2 films, the investigated layers were deposited on the sub-strates with Cr contact pads previously prepared by vacuum resistive evaporation. Before Cr deposition the substrates were chemically treated and then heated in vacuum in the temperature range 600-700 K. The thickness of the chromium pad was about 1000 nm. Studies of the electric field-induced properties were carried out in vacuum (in the growth chamber in situ) as well as in open air at normal atmospheric conditions and under applied electric field up to 105 V/m.  3. STRUCTURAL INVESTIGATIONS  Two sets of films were selected for structural stud-ies: the first family of as-grown layers (glass substrate, Ts  300 K) and the second group of specimens deposit-ed on the glass substrate at the room temperature after annealing in air under normal atmospheric conditions. As is shown in Fig.1, the film microstructure is characterized by presence of small disperse particles. The microcrystalline phases are good seen in the elec-tron-diffraction patterns. The electron beam-induced anneal leads to the film crystallization and re-evaporation of tellurium. After annealing in air under  V.I. BILOZERTSEVA, D.A. GAMAN, H.M. KHLYAP, ET AL. J. NANO- ELECTRON. PHYS. 4, 01019 (2012)   01019-2 normal atmospheric conditions at T = 373-393 K nano-crystals Bi2Te3 and NaTe3 as well as nanoparticles are observed (see Fig. 2).  The heat treatment of the films in air is accompa-nied by the formation of BiO3 and TeO2 oxides.    Fig. 1 – TEM image, diffraction and microdiffraction pat-terns of the NaBiTe2 films with 30 nm thickness deposited on the glass substrate at Ts = 300 K under deposition rate 0.1 nm/s (the original sample)    Fig. 2 – TEM image, diffraction and microdiffraction pat-terns of the NaBiTe2 films with 80 nm thickness deposited to the glass substrate at Ts = 300 K under deposition rate 0.5 nm/s after annealing in air under normal atmospheric conditions  4. RESULTS OF ELECTRICAL MEASUREMENTS AND THEIR DISCUSSION  Electrical measurements were performed at the room temperature under applied electric field up to 104 V∙m–1. The current-voltage characteristic of the film is illustrated by the Fig. 3. As it is shown, this dependence is of exponential character typical for metal-semiconductor structures. Such a characteristic may be qualitatively described as follows:   j(E) ~ j0exp[(eEdtun+ )/kBT], (1)  where E is the applied electric field, dtun is the distinctive tunneling length,  is the tunneling parameter defined numerically, and j0 stands for a saturation current [7].    Fig. 3 – Room-temperature current-field characteristic of the investigated sample (Cr-contacts)  For more detailed study of current mechanisms in the investigated structure the experimental curve was rebuilt in semi-log and double log scales (Fig. 4, a, b).    a    b  Fig. 4 – Semi log current-field characteristic of the investi-gated sample (Cr-contacts) (a) and double-log one (b)  NANOSTRUCTURED NABITE2 THIN FILMS … J. NANO- ELECTRON. PHYS. 4, 01019 (2012)   01019-3 Double-log recalculation of the experimental cur-rent-voltage dependence shows the smooth superposi-tion of at least three modes of the carriers transport:  current caused by the carriers injected from the metallic contact under the applied voltage 50-100 V [8];  velocity-saturation regime under the applied volt-age up to 120 V, where I ~ (2εε0vsatVa/L2), vsat is de-termined from the experimental data and L is the thickness of the film;  The current governed by so-called “3/2”-law as the applied voltage increases: I ~ (4εε0/9L2)(2e/m*)1/2(Va)3/2. The time evolution of the film conductivity is also interesting. Fig. 5 illustrates this dependence for the as-grown films. As is shown (Fig. 5), the conductivity of the film rapidly decreases during first 30 min of meas-urement and then monotonously decreases during fol-lowing 50 min.     Fig. 5 – Time dependence of the current flowing through the investigated NaBiTe2 film in vacuum after its preparation  The experimental dependence j(t) can be qualita-tively described as    j(t) ~ j0∙exp(– t/ ), (2)  where j0 and  are the initial current density and so-called stabilizing time, respectively. Both terms are functions of the film parameters in vacuum (the carri-ers’ mobility and scattering mechanism on the surface relief are crucial).  5. GAS SENSITIVITY INVESTIGATIONS  Optical and surface properties before and after NO exposure were studied. In order to examine gas sensitivity the as-grown films were placed in the closed chamber with different NO concentration at the room temperature. Fig. 6 plots experimental transmission spectra of the investigated samples after interaction with nitro-gen monoxide of various concentrations. As is shown, the films demonstrate significant changes of their opti-cal characteristics even at low concentrations of the aggressive gas. As the nitrogen monoxide concentration increases, the transmission of the examined layers is also increasing (Fig. 6). After the NO exposition the film relief is significant-ly changed. Fig. 7 presents the typical AFM image of the as-grown sample (a) and after NO exposure (b). The standard image numerical processing enabled to esti-mate the parameters of the surface roughness (Table 1), where: Ra is a medial roughness of profile; Rq is a root-mean-square roughness of profile; Rz is a medial roughness of a profile on 10 points.    Fig. 6 – Transmission spectra of the original NaBiTe2 film and after nitrogen monoxide exposure under concentration: 10 mg/m3 and 106 mg/m3 during 60 min, sensor operating temperature 300 K     a    b  Fig. 7 – AFM image of NaBiTe2 film surface (the as-grown sample) (a) and after NO exposure (b)  V.I. BILOZERTSEVA, D.A. GAMAN, H.M. KHLYAP, ET AL. J. NANO- ELECTRON. PHYS. 4, 01019 (2012)   01019-4 Table 1 – Roughness of NaBiTe2 film surface before and after NO exposition  Roughness Initial No Ra, nm 0.9 0.3 Rq, nm 1.2 0.5 Rz, nm 5.5 1.9  Another important question is how the conductivity of the films changes under exposure of different ag-gressive environments. The time profile of the DC cur-rent flowing through the sensor in response to adsorp-tion and desorption of different gases as a very im-portant characteristic of the device [9] had been also investigated. Fig. 8 demonstrates current response curves meas-ured after undergoing the examined samples to sulfur hydroxide (a) and NH3 (b) gas exposure at the room temperature. These data point out sensitivity and re-sponse of the films to NH3 and H2S exposure. As one can see, the reversible adsorption takes place, but the problem of time stability is to be solved. So that, this material appears to be perspective in gas sensors de-velopment.           a b   Fig. 8 – Current response of the investigated NaBiTe2 thin film at different concentration of H2S (a) and NH3 (b), sensor operating temperature 300 K  6. CONCLUSIONS  We yielded NaBiTe2 thin films on glass substrates. The structure of our samples is microcrystalline with typical grain size about 30 nm. Anneal leads to the film recrystallization, evaporation of tellurium and oxidation. Charge transport mechanism was also investigated. It was determined that time dependence of the film conductivity under applied DC electric field is caused by different processes of the carriers’ injection and sur-face recombination. Room-temperature current-voltage characteristics revealed a smooth superposition of drift-diffusion current, velocity saturation mode and ballistic regime at the all range of applied voltage (0-140 V).  The influence of some aggressive gases on NaBiTe2 films properties was studied for the first time. The op-tical transmission and surface relief changes under interaction with NO. Adsorption of such atmospheric impurities as H2S and NH3 result in conduction drift. So NaBiTe2 thin films appear as perspective objects for gas sensors development.  ACKNOWLEDGEMENT`S  Authors are grateful to Prof. S.N. Grigorov for technical help and to Prof. V.I. Perekrestov for useful discussions.   Наноструктурные тонкие плёнки NaBiTe2 и их свойства  В.И. Белозерцева1, Д.А. Гаман1, Г.М. Хляп2, А.А. Мамалуй1, Н.Л. Дьяконенко1, Л.Г. Петренко1  1 Национальный Технический Университет «Харьковский Политехнический Институт», ул. Фрунзе, 21, Харьков, 61002 Украина 2 University of Technology, Distelstr.11, D-67657 Kaiserslautern, Germany  В статье представлены наши экспериментальные результаты по росту, морфологии, оптическим  и электрофизическим свойствам тонких пленок NaBiTe2, выращенных термическим испарением в ва-кууме. Изложены результаты структурных исследований и электрических измерений пленок NaBiTe2 с Cr контактами. Также обсуждаются временные зависимости тока, протекающего через исследуемые структуры при постоянном приложенном электрическом поле при комнатной температуре. Впервые описано влияние некоторых агрессивных атмосферных примесей на характеристики пленок NaBiTe2.  Ключевые слова: Тонкие плѐнки, халькогениды, NaBiTe2, структура, поверхностный рельеф, опти-ческое пропускание, электрические свойства, механизмы зарядопереноса, газовая чувствительность.   NANOSTRUCTURED NABITE2 THIN FILMS … J. NANO- ELECTRON. PHYS. 4, 01019 (2012)   01019-5 Наноструктурні тонкі плівки NaBiTe2 та їх властивості  В.І. Білозерцева1, Д.О. Гаман1, Г.М. Хляп2, А.О. Мамалуй1, Н.Л. Дьяконенко1, Л.Г. Петренко1  1 Національный Технічний Університет «Харківський Політехнічний Інститут», вул. Фрунзе, 21, Харків, 61002 Україна 2 University of Technology, Distelstr.11, D-67657 Kaiserslautern, Germany  У статті представлені наші експериментальні результати по росту, морфології, оптичним  і елект-рофізичним властивостям тонких плівок NaBiTe2, що було вирощено термічним випаром у вакуумі. Докладені результати структурних досліджень та електричних вимірів плівок NaBiTe2 з Cr контак-тами. Також обговорено часові залежності струму, що тече через ці структури при постійному прикла-деному електричному полі при кімнатній температурі. Вперше описано вплив деяких агресивних ат-мосферних домішок на характеристики плівок NaBiTe2.  Ключові слова: Тонкі плівки, халькогеніди, NaBiTe2, структура, поверхневий рельєф, оптичне про-пущення, електричні властивості, механізми зарядопереносу, газова чутливість.    REFERENCES  1. F.F. Volkenstein, Electronic processes on the semiconduc-tor surface under chemisorptions (Moscow: Nauka Pub-lishers: 1987). 2. M. Takahashi, M. Kojima, S. Sato, N. Ohnisi, J. Appl. Phys. 96, 5582 (2004). 3. L.N. Lukyanova, V.A. Kutasov, P.P. Konstantinov, Semi-conductors 47, 224 (2004) (in Russian). 4. M. Ulrich, A. Bunde, C. Kohl, Appl. Phys. Lett. 85, 242 (2004). 5. G.M. Khlyap, V.I. Bilozertseva, S.D. Ovcharenko, N.L. Dyakonenko, Thin Solid Films 453, 154 (2004).  6. V.I. Bilozertseva, A.A. Ryabchun, N.L. Dyakonenko, L.G. Petrenko, S.D. Gapochenko, Photoelectronics 12, 20 (2003). 7. Ng. Kwok, Guide to Semiconductor Devices, (New York: Wiley: 2002). 8. B. Braunecker, D. Feldman, J. Marston, Phys. Rev. B 72, 125311 (2005). 9. JC Hsieh, CJ Liu, YH Ju. Thin Solid Films 322, 98 (1998).    

Nanostructured NaBiTe2 Thin Films and Their Properties

https://essuir.sumdu.edu.ua/bitstream/123456789/20541/1/5.pdf

Nanostructured NaBiTe2 thin films and their properties

Abstract

Similar works

Full text

Available Versions

Electronic Sumy State University Institutional Repository

SocioEconomic Challenges Journal (Sumy State University)

Electronic Sumy State University Institutional Repository