Case Report
Effect of Infrared Radiation on the Hydrogen in Thin Films Double Barriers Based Melt SiliconeGermany
BA Najafov^{1}, GI Isakov^{2} and FP Abasov^{1}*
^{1}Institute of Radiation Problems of Azerbaijan National Academy of Sciences, Azerbaijan
^{2}Institute of Physics of Azerbaijan National Academy of Sciences, Azerbaijan
Abasov FP, Institute of Radiation Problems of Azerbaijan National Academy of Sciences, Baku, AZ1143, str. B. Vahabzadeh, 9, Azerbaijan.
Received Date: December 08, 2018; Published Date: December 17, 2018
Abstract
Possibilities of plasma chemical deposition of αSi_{1x} Ge_{x}:H (x=0÷1) films undoped and doped with PH_{3} or B_{2}H_{6} have been analyzed from the viewpoint of their application in pin structures of solar cell. The optical properties are considered, and the amount of hydrogen contained in those films is determined. The film properties are found to strongly depend on the film composition and the hydrogenation level. The number of hydrogen atoms in the films is varied by changing the gas mixture composition, and IR absorption in αSi:H and αG_{e}:H films is measured. The αSi:H and аSi_{0,88}Ge_{1,2}:H films were used to fabricate threelayer solar with an element area of 1,3 sm^{2} and an efficiency (η) of 9.5 %.
Keywords: Effect infrared on thin films; Amorphous silicon; Solar cells; Efficiency; Optical properties; Oscillator; Absorption coefficient; Effusion of hydrogen; Deposition rate
Introduction
Introduction of Si films and its alloy characterized by various structural phases. The most interesting of them are crystals that are in the amorphous matrix. Such alloys are produced by different methods at different technological regimes. For films of amorphous hydrogenated silicon and aSi: H, formed by the method of cyclic sedimentation annealed in hydrogen plasma effect Staeblera Vronsky is expressed weakly [1]. Authors [2] note the absence of the effect of StajebleraVronsky in Nanostructure films of aSi:H film Silicon alloys crystallization of aSi: H is carried out by various methods: long annealing in vacuum at 600 °C, fast heat treatment [3], laser annealing [4] and ion implantation [5]. The mobility of the charge carriers, alloying and efficiency optical absorption coefficient in films of aSi: H vy she than crystalline silicon. Films aSi_{1x}Ge_{x}: H are an effective and inexpensive material for making solar cells and other electronic devices [6, 7].
In this regard, the receipt of the aforementioned films and changing their conductivity type are actual tasks. [8] shows that with the change in the temperature of the substrate grow Nano crystals increases. Found that with increasing concentration of average grain size decreases RN3 (d) and the proportion of crystalline particle volume (Vc). When alloying with increasing concentration of boron, B_{2}H_{6}, value (d) does not change, and Vc is reduced. The value of photo films and efficiencySi_{1x}Ge_{x}: H, somewhat lower than in aSi: H [9, 10]. With the changing conditions of technology and technological parameters of hydrogen deposited on various structural phases: microcrystalline, polycrystalline, Nana crystalline, etc. of energy conversion efficiency based on Schottky barrier in films of aSi: H was 5.5%. Attempts have been made to obtain high efficiency solar cell (CPA ASE) (~ 9.0%) on the basis of aSi_{1x}Ge_{x}: H [11]. Most literature data show that when using amorphous silicon and SiliconGermanium alloys in solar cells with multilayered or cascading structure have the greatest EFFICIENCY ~ 8.5% [12]. Based on the above stated the purpose of this work is to determine the amount of hydrogen in amorphous films method for optical solid solution aSi_{1x}Ge_{x}: H (x = 01) and manufacturing of solar cells based on them.
The Experimental Part
Thin films of aSi_{1x}Ge_{x}: H (x = 01) received plasma chemical deposition method using gas mixtures of H_{2} + SiH_{4}, U + GeH_{4} in various proportions. Details on obtaining films shown in [11, 12]. Plasma RF field created through mainly inductive coupling. Film thickness was 0.1 ÷ 1.0 μm. Measured absorption coefficient (α), refraction (n), reflection (R), (T), width of band gap (E0) for each sample, using appropriate models [13.14]. Optical absorption at room temperature were studied by the method of [1316] on spectrometer x29.
Result and Discussion
The hydrogen concentration in aSi_{1x}Ge_{1x}: H, (x = 0 ÷ 1) films is determined using the method of Brodsky et al. [14  17]:
where N is the number of Avogadro and (ξ) the integral strength of the hydride with units cm2/mole (g/ξ) = 3.5. If the width of the absorption indicate through and center frequency ω*, ω_{0}, when Δ ω/ω_{0} ≤ 0.1 after approximation with a tolerance of ± 2%, equation (1) can be written as follows:
where is: ε dielectric constant. For Si, ε=12; Ge, ε =16.
If the equation (2) preintegral expression Relabel АSи – the cumulative uptake of fashion streching for each film, then in determining hydrogen concentration (NH) get a general expression in abbreviated form:
Coefficient А_{S}– for films aSi:H, is in the field of fashion stretching 1,4∙1020 см^{2}. Absorption coefficient (α) for these phones (2100 см^{1}) is 8∙101÷3∙102см^{1} When this NH=7∙1021÷2,1∙1022 см^{3}. For films аGe:H АS =1,7∙1020 см^{2}. In films aSi:H and аGe:H absorption frequencies 2000 и 1980 сm^{1} is caused by fluctuations in the type of valance and absorption frequencies 630 и 570 см^{1} oscillations of type bend (fig. 1a and 1 c).
Thus, for аSi_{1x} Ge_{x}:H the place has a significant overlap, which is observed in the spectrum of IR absorption for both bands stretching Ge:H (1980 см^{1}) and Si: H (2000 см^{1}), and for bending strips around the frequency 600 сm^{1} (fig. 1б) [5, 12]. It is clear that the equation (3), so did the links stretch fashion oscillating characterizes in films аSi:H, аGe:H и аSi_{1x}Ge_{x}:H. Assess the relative binding hydrogen to hydrogenated amorphous аSi_{1x}Ge_{x}:H:
Where is NSiH и NGeH – hydrogen concentration in аSi:H и аGe:H (в см^{3}). Equation (3) You can rewrite to fashion swings (waggingmode) films аSi:H и аGe:H. Thus the value of the NSiH и NGeH are determined from equations (3) to fashion rocking in the following form:
where is, – the cumulative uptake of fashion swinging for films аSi:H и аGe:H. For specified films Aw=1,6∙1019 см^{2} и Aw=1,1∙1019 сm^{3}, accordingly. Knowing NGeH (where, for films аGe:H, Aw=1,6∙1019 см2 and α=5∙101 см^{1}), calculate hydrogen concentration N_{H} in the film аSi_{1x}Ge_{x}:H in the words of:
where is, – number of links, some of the effects of net swing аGe:H, the value which, calculated according to the equation (5). The second factor in the expression for NH (cumulative ratio of IR absorption maxima) is a vibrational fashion stretching in the sample and in pure aGe: H. For the computation of the cumulative ratio used maximum satisfying the oscillatory fashion stretching GeH (2000 см^{1}) in the film аSi_{1x}Ge_{x}:H.
From these data it is possible to evaluate the effect of the oscillator in film аSi_{1x}Ge_{x}:H the ratio of: Q = J_{S}/J_{W},
where is, – are integrated acquisitions fashion, stretching and rocking, accordingly. The oscillator strength Q= 0,51 (for х=0) и Г=0,13 (for х=1). The maximum value Р=4,16 for х=0,40.
Table 1 shows the characteristic parameters of amorphous films аSi_{0},60G_{e} 0,40:H. On Figure 2 shows the distribution of hydrogen on film thickness d: certain 1 method of recoil protons, 2 method of IR absorption spectrum. You can see, the distribution of hydrogen sufficiently uniform. Unlike other methods, the method of recoil protons (MOP) sample bombing beam of protons. When researching аSi:H and its alloys, this allows you to get distribution hydrogen on thickness ~ 40 ÷ 100 Å. Method of calibration accuracy is limited only by the MCS, which is determined by the largest concentration of hydrogen (NH), and IR spectroscopy of found values that match 2 ÷ 3 %. This method provides information about the General content of both associated and not associated with Si hydrogen. А, with regard to the precise definition of hydrogen content in the volume of films, this band was analyzed INFRARED absorption 630 сm^{1}. To clarify the amount of hydrogen is embedded in amorphous matrix below as follows is determined by the structural parameter (R):
Table 1: Characteristic parameters of amorphous films aSi_{0,60} Ge_{0,40} :H.
where is J_{2000} и J_{2100} – intensity of absorption bands at 2000 и 2100 см^{1}. Using the equation (3), of this ratio is determined by the concentration of hydrogen. Increase R occurs simultaneously with a decrease in the concentration of hydrogen. The highest magnitude R (before 0,8) observed for films аSi:H, the besieged plasma chemical deposition method (ПХО), when TS=300 0С, power frequency discharge W=100W. However, the films studied in the present work, that when TS=200 ÷ 300 0С, micro structure parameter cannot vary in the range R= 0,1 ÷ 0,8. When annealing during 30 minutes in a vacuum at R value reaches 1.0. Accordingly, in this case, СH is 24.5 ÷ 14.0 at. %. By number of links SiH, you can define a specific concentration of hydrogen containing links [Si–H]/[Si]. Specific concentrations of hydrogen containing Silicon links in the maximum reaches the value 0.58 [10–12].
Hydrogen concentration (NH), some effusion method, correlated with the concentration of hydrogen, calculated using the integrated force IW, fashion rocking 600 см^{1} (рис. 3). The number of hydrogen atoms is found by at. % (СH), effusion method is defined for the data tapes and compared to the number of hydrogen atoms NА (Avogadro’s number).
 the film received when hydrogen pressure 0.6 mTorr.
 the film received when hydrogen pressure 1.2 mTorr.
 the film received when hydrogen pressure 1.8 mTorr.
 the film received at a pressure of hydrogen 2.4 mTorr.
 the film received when hydrogen pressure 3.0 mTorr.
Therefore, the ratio of compared to СH (ат. %) (fig. 3). Change СH (at. %) for films at various temperatures heat up, shown in the table 1. Found that after effusion, during heat treatment up to 650° c, hydrogen concentration is NH=1,3 ат. %. In doing so, found that the strength of the oscillator depend Q on hydrogen concentration (NH), It decreases after effusion of hydrogen; with increased hydrogen content (РH2) in the atmosphere of the received films аSi_{0,60}Ge_{0,40}:H When partial pressures from 0.6 to 3.0 m Torr power oscillator increases [5, 12]. This is due to the hydrogen containing links Ge:H, Si: H at specified frequency.
Heating the sample in a closed volume is due to the fact that the material almost completely decomposed into its constituent elements, with crystallization temperature range 350 ÷ 650 0С, what causes hydrogen jeffuziju and leads to increased pressure. Pressure measured capacitive pressure gauge with a precision of 0,1 %. To determine the effusion other gases should undertake quantitative mass spectrometric analysis of the composition of the gas. Note that the hydrogen inside the film identifies several ways: at. %,NH, РH2 and Р. To define these settings, you must remove the IR absorption spectra of the corresponding frequency fluctuations associated with the absorption of hydrogen.
Optical properties of thin films
The dependence of (αhν)^{1/2} from hν to determine the width of the forbidden zone [14, 16] for each film.
In all the studied films of the optical absorption edge ratio describes the ratio of:
where is, α = 5∙104 cm^{1}, E0  optical band gap width for each film, В – the coefficient of proportionality. The value of the В determined by extrapolation of dependencies (αhν)^{1/2} from hν for each sample. Quadratic dependence (7) received in theory model [13,14], Describes the density of States slit mobility. The value of the В when х=0÷1 at. % Ge, for films аSi_{1x}Ge_{x}:H changes from 527 before 343 eV1cm1/2, accordingly, E0=1,86 eV and E0=1,14 eV. Means with increasing content of Germany, E0 decreases. Mobility of carriers and photoconductivity in film аSi_{1x}Ge_{x}:H, also diminishes when Germany more 40 at.% [11, 12]. We use the known relative absorption coefficient α  is determined from the following equation [14  17]:
here take, that
For weakly absorbing light areas k^{2}_{0}≤(n −1,5). к_{0} shows light attenuation in the substrate. Note that the film thickness d, defined in this case, the relevant transmission or reflection from extreme interference fringes.
From equation (8), the coefficients of absorption (α) are defined as follows:
Then,
Equation (11) is a working formula for determining optical absorption coefficients for films, in a weakly absorbing spectral region.
In a strongly absorbing spectral regions R_{3} = 0, R_{2} = R_{1} = R, n(λ ) = const and n = n_{1} =1,5 for glass substrates, а n = n_{1} = 3,42 for silicon substrate. Then equation (8) can be rewritten as follows:
then,
This formula can be used to determine the coefficient of optical absorption in a strongly absorbing spectral regions. Accordingly, the coefficients of refraction is defined using the following ratio:
or by using the following formula:
where is λ_{m}, λ_{m1} – the wavelength corresponding to the neigh bouring extreme and spectra of transparency or reflection (corresponding frequency, с the speed of light. Refractive index is defined or the following formula [15]:
where is T_{max} и T_{min} – functions of the wavelength λ, n_{1} – index of refraction of the substrate, which is defined by the expression:
where is T_{1} – deletion of the substrate, which is almost always in the area of transparency. As for glass substrates T_{1} = 0,91, то n_{1}= 1,554. Accordingly, the film thickness is calculated by the formula:
where is λ_{1} и λ_{2} – wavelengths which correspond to the neigh pouring extreme points on the spectrum bandwidth, А=1 for two extremes of the same type (max– max, min– min) and А=0,5 for two adjacent extremums of the opposite type (max– min, min– max).
Creation of solar cells
Studies show that films аSi_{1x}Ge_{x}:H (x≥0,20) can be used as a qualitative material in semiconductor electronics [12]. For this purpose, we have developed a 3item based on two elements of cascade type. Threelayer element is made of 2layer element consisting of two elements on the basis аSi:H с pin transition and pin element with i a layer of film аSi_{0,88}Ge_{0,12}: H. The thickness ilayers to the top two transitions selected in such a way that respected the condition of equality of shortcircuit current lower element. Short circuit current was about half the value for an element with a pin transition. Idling voltage and short circuit current decreases with increasing number of superimposed layers. This way you can build multiple layers (create nlayer element). Note that for each item produced i0.5 μm thick layer. The area of each element was 1.3 cm^{2}. When receiving a threelayer solar cells must be respected uniform thickness and square to each element. Substrate material of steel and was chosen as the cover used ZrO_{2} with missing light 80%. Covering the same time playing the role of upper ZrO_{2} (front) of the contact. The thickness of the layers of aSi:H pand ntypes was ~300 and 400Å, respectively. For alloying films number of В_{2}Н_{6} and РН_{3} in gas mixtures changed within Alloy films in gas mixtures changed within 0.1 and 0.5%, respectively. After the deposition of amorphous semiconducting layers deposited by evaporation film ZrO_{2} thickness ~ 500 Å. The upper contacts used Ni/Ag, for lowerstainless steel substrate. Items covered source sunlight provided АМ^{1} (100 mW/sm^{2}). Shortcircuit current for 3layer elements was 8,5 mA/cm^{2}, noload voltage ~ 2,25 V, fill factor ~ 0,50 and CPA ~ 9,5% (рис.4). CPA for singlelayer and doublelayer element is 7% and 8.9%, respectively. The effectiveness of collecting media when different wavelengths is defined by the formula:
where is J_{ф}(λ) – the photocurrent density (10 mA/cm^{2}), N(λ) – the number of photons incident per unit surface per second, e free media charge.
For elements with the structures of the shortcircuit current is calculated in the supposition of a complete depletion of all layers, in the absence of direct bias. Thus, the short circuit current for the first, second, and third elements provides the following expressions:
where is, W_{i}, W_{n}, Wp field distribution inside the i, n, p layer, respectively, N_{ph} – the number of photons incident on the surface of the elements, R – reflectivity film, α – absorption coefficient for each layer elements.
Idling voltage for cascading elements with two and three transitions is presented as:
The fill factor for all elements of the set size 0.5. Shortcircuit current of a cascading element with two sets of values less transitions I_{sc}(II) sets the lower value I_{sc1} and I_{sc2} . Shortcircuit current of a cascading element with three passages is determined by the smallest amount of I_{sc1}, I_{sc2} or I_{sc3}.
CPA of many transitional cascade elements is given by the expression:
where is i = 2 and 3 – shows the number of layers, P_{in} – power of incident light to the surface elements, its value is 100 mW/cm^{2}, E_{01}, E_{02}, E_{03} – Accordingly, the width of the forbidden zone for each i the layer.
To raise η for solar cell, you want to increase the number of layers reduce the area elements, the choice of metal wires to reduce the resistance of the metal contacts, etc. Measurement of spectral sensitivity is usually produced at a constant illumination with white light, the intensity of which corresponds to the normal conditions of work (AM1~100 mW/cm^{2}), at the same time an element falls modulation calibrated monochromatic radiation. Photocurrent and its dependence on wavelength of monochromatic radiation is measured in shorted circuits by using synchronized amplifier. To determine the effectiveness of collecting important knowledge of the electric field which is passed to the element. It has been noticed that in device dependently to the configuration collection efficiency is offset from red light in the blue spectrum. It is known that the photon energy and momentum of the corresponding electromagnetic wave with frequency and wavelength in vacuum, equal:
where is, h Planck’s constant. When agile frequencies ν  the preponderant role played by wave properties, at large ν  particle properties of light. If P* electromagnetic radiation energy feeding okay on some surface unit area for 1 sec, cthe speed of propagation of light waves in a vacuum, Rreflectivity surface pressure plight on this surface as well:
light pressure (P) is defined by equation (20) and represent the following form:
N the number of incident photons. W photon energy falling at all wavelengths of the body surface. P* momentum light falling on dies surface for 1 sec. Then the pressure of the incoming light is defined in the following form:
F  the power of light pressure (F=10^{8} H) on the surface (S=1cm^{2}), λ  incident wave length, t  time of incidence of the light for 1 sec. with energy P* and its value is Nhν photons, with the momentum of each photon is equal to hν/c. With radiation reflection R, λ the number falling photon is 10^{17}÷10^{18} м^{2}с^{1}, λ = 300 ÷ 900 nm (fig. 4).
Conclusion
Obtained thin films аSi_{1x}Ge_{x}:H (х=0÷1) plasmachemical deposition method using gas mixtures of H_{2} + SiH_{4}; H_{2}+GeH_{4} in various proportions. It was determined that the highest R value (up to 0.8) is observed for films of aSi: H deposited method (PHO) at temperature t = 300° c, with an output frequency of discharge W = 100 W. The data on the ratio of The oscillator strength in the film was evaluated аSi_{1x}Ge_{x}:H, где Oscillator strength Q=0,51 (for х=0) and G=0,13 (for х=1). For х=0,40 the maximum value Р=4,16.
Based on the films аSi:H and аSi_{0,88}Ge_{0,12}:H manufactured solar cells and created singlelayer, doublelayer and threelayer structure; their characteristics are measured. Found that for singlelayer, doublelayer and threelayer structures with an area element 1,3 cm^{2} η is 7 %; 8,9%; 9,5%, accordingly. For the three layered element highs move in the scope of collection efficiency of longer wavelengths. In the reporting structures of their light in the wavelength interval 0,3 ÷ 1,1 μm within 120 hours, there has been no degradation. It is shown that the multilayer structure solar cells based on αSi_{0,88}Ge_{0,12}:H and αSi:H effective, and the improvement of their Efficiency are relevant tasks.
Acknowledgement
None.
Conflict of Interest
No Conflict of Interest.
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BA Najafov, GI Isakov, FP Abasov. Effect of Infrared Radiation on the Hydrogen in Thin Films Double Barriers Based Melt SiliconeGermany. Mod Concept Material Sci. 1(1): 2018. MCMS.MS.ID.000504.

Infrared Radiation, Plasma Chemical, Structures of Solar Cell, Optical Properties, Film Properties, Film Composition, Hydrogenation Level, Gas Mixture Composition, IR Absorption, Fabricate ThreeLayer Solar, Effect Infrared on Thin Films, Amorphous Silicon, Solar Cells, Efficiency, Optical Properties, Oscillator, Absorption Coefficient, Effusion of Hydrogen, Deposition Rate, Technological Regimes, Amorphous Hydrogenated Silicon, Cyclic Sedimentation Annealed, Hydrogen Plasma Effect, Silicon Alloys Crystallization, Technological Parameters, Microcrystalline, Polycrystalline, Nana Crystalline.

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