Primary results or synthesis and characteristics of thin-film materials for PV converters. Work performed by 4-point-probe method, Hall effect, magnetron sputtering, electron microscopy.

1. Characterization of electrical properties of Mg(Zn)SnN2 films
ABSTRACT
The fast growth of the semiconductor industry together with environmental pollution and lack of clean energy created binding demands upon new materials. MgSnN2 is reported as still unexplored with accurate
electrical properties consisting of earth-abundant highly recyclable elements. Based on previous experiments with the narrow bandgap semiconductor ZnSnN2, series of samples of crystalline thin films MgSnN2
were deposited using magnetron sputtering at room temperature. Measuring electrical properties by the four-probe method and Hall effect confirmed, that samples exhibit semiconducting properties. MgSnN2
with a rocksalt structure is expected to make an analog to GaN, and with its wide bandgap (above 2 eV) can provide new alternatives for LEDs and other optoelectronic devices.
INTRODUCTION
The depleting of mineral reserves, deteriorating of the natural environment and
the need to generate more and more electricity has led to an active search for
alternatives in energy production. Reducing carbon dioxide (CO2) emissions is at
the main aspect of the world’s transition from fossil fuels towards renewable
forms of energy. This encourages researchers to the intensive study of
photovoltaic converters with good efficiency, non-toxicity, and earth-abundant
materials that are easily recyclable and can be synthesized through a scalable
process [1].
ECONOMICAL BENEFITS OF USING SOLAR ENERGY
An important aspect of choosing elements to use for further manufacturing is
costs. Figure 9 shows the relative price of Ga, Sn, and Mg, were clearly
demonstrated Ga being more expensive than [6].
Considering electrical properties research in Granta Edupack showed that
although the resistivity of nitrides is higher, but comparing to Germanium or
Gallium price is more than twice lower. Other generated graphs in the same
software showed a decreased CO2 footprint.
Overall, solar energy is rapidly reaching the market. The cost of manufacturing
solar panels has fallen sharply. Comparing to other renewables, solar energy use
is increasing (Fig. 10), moreover research is becoming more rapid (Fig. 11).
If there is one product that can outperform crystalline silicon solar panels, it is a
thin-film module. The percentage of its use fall due to the high cost and toxity.
Therefore, the invention and application of new materials is necessary for
market development.
Moreover, ternary nitrides, have been reported to be p-doped (unlike III-V). This
capability of semiconductors together with other unique characteristics are
important and can replace their predecessors.
From the literature study, few variations of lattice constants and bandgaps,
which are decisive in controlling electronic properties important to devices were
distinguished:
Because MgSnN2 has not been previously synthesized, the growth of the
samples was based on previous knowledge obtained by growing ZnSnN2 by
magnetron sputtering. The percentage of Mg/Sn elements was changed for
completeness of the study, as well as the substrate (silicon and glass).
After applying 100 oC a shift of resistance happens. In a semiconductor, in certain temperature ranges, the conductivity increases rapidly with increasing temperature. When
reaching a particular temperature the conductivity begins to decrease again just as in metals. In addition, at lower temperatures, carriers move slowly, so they have more
time for interacting with charged impurities. At the same time, with increasing temperature, vibration in the lattice structure changes the energy of electrons. Overall
measurements showed that samples behave as semiconductors.
By the Hall effect, we can determine not only resistance but also the conductivity type, carrier concentration, and mobility. Results of the study of electrical properties by
Hall effect using contacts can be slightly different, as explained by The van der Pauw Method [5]. In-Sn contact was placed on the very corners (to avoid electricity loss) of the
same samples. Performing of new measurements showed decreasing of resistivity even more (final Table 3 and Fig. 7)
0.00E+00
1.00E+01
2.00E+01
3.00E+01
4.00E+01
5.00E+01
6.00E+01
7.00E+01
0.58337
0.56275
0.54165
0.53565
0.51809
0.5055
0.48189
0.47869
0.4663
0.45683
0.45561
Resistivity
ratio Mg/Sn
0.00E+00
1.00E-01
2.00E-01
3.00E-01
4.00E-01
5.00E-01
6.00E-01
7.00E-01
0.5055 0.48189 0.47869 0.4663 0.45683 0.45561
Resistivity
ratio Mg/Sn
resistivity without contact
resistivity with contact
resistivity 4 point probe
Sample
Thickness,
mkm
ratio
Mg/Sn
ρ (Hall)
ρ (Hall)
with contact
ρ (4-point-
probe)
Hall coef.
Hall coef. with
contact
MSN-29 1.77 0.58337 6.63E+01 3.33E+01 3.09E+01 -2.27E+02 -2.52E+00
MSN-30 1.74 0.56275 4.40E+01 2.31E+01 1.14E+01 6.48E+02 -1.54E+00
MSN-31 1.77 0.54165 1.24E+01 7.31E+00 2.99E+00 1.24 -4.27E-01
MSN-32 1.84 0.53565 5.45E+00 2.98E+00 1.34E+00 -1.97 -2.18E-01
MSN-33 1.85 0.51809 2.29E+00 1.19E+00 7.80E-01 -4.15E-01 -3.97E-02
MSN-34 1.84 0.5055 5.10E-01 5.88E-01 3.51E-01 -3.39E-02 -1.80E-01
MSN-35 1.86 0.48189 2.56E-01 3.43E-01 2.56E-01 -1.60E-02 -4.81E-02
MSN-36 1.91 0.47869 1.96E-01 2.42E-01 2.05E-01 -3.51E-02 -5.78E-02
MSN-37 1.95 0.4663 1.18E-01 1.90E-01 1.54E-01 -1.68E-02 -1.84E-01
MSN-38 1.96 0.45683 9.85E-02 1.18E-01 1.07E-01 -1.57E-02 -3.97E-02
MSN-39 1.96 0.45561 7.93E-02 9.58E-02 9.67E-02 -2.07E-02 -3.76E-02
ELECTRON MICROSCOPY RESULTS
The best first way to examine thin-film samples is electron microscopy. It is more profitable to begin with scanning microscopy analysis, which will provide information about
the structure of the samples and will give a clear picture of the surface [18]. It is assumed that the selected samples have different concentrations of elements, which may
affect the grain size and distance between them, as well as the orientation.
As expected from the comparisons of the results of measuring the characteristics of samples grain size increased slightly with nitrogen flow respectively. At the same time,
the percentage of oxygen decreased depending on N%.
6
8
10
12
14
O%
Sample N at% O at% Mg at% Sn at% raitio Mg/Sn
MSN-29 44.4 10.1 26.5 18.9 0.58
MSN-30 43.1 12.1 25.2 19.5 0.56
MSN-31 44.4 11.2 24.1 20.3 0.54
MSN-32 46.6 9.5 23.5 20.4 0.53
MSN-33 45.7 9.6 23.2 21.5 0.52
MSN-34 47.2 7.3 22.9 22.5 0.50
MSN-35 47.2 8.1 21.6 23.2 0.48
MSN-36 47.1 7.9 21.5 23.4 0.48
MSN-37 47.3 7.7 21.0 24.0 0.47
MSN-38 48.7 6.8 20.3 24.2 0.46
MSN-39 48.3 6.6 20.5 24.5 0.46
Mines Nancy
Département Matériaux
Program: Multiscale materials
Research project in 3A of Mines
Nancy
ECTS: 8
Project report completed by
Nelia Zaiats
Supervisors: Jean-François Pierson, Fahad Alnjiman, Agathe Virfeu
Date: 25/01/2021
GROWTH METHODS
In work [2] successful growth of material by chemical vapor
deposition is described. The same type of films was made by
molecular beam epitaxy in work [3]. As can be seen from
parameters, lattice constant measured along work [3] is higher than
in [2], which theoretically gives better conductivity due to tightly
bound of electrons to the atom.
Figure 2 - Changes in concentrations of oxygen
Table 2 – Concentration of elements
Figure 1.1 – Surface pictures MSN-29
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Ohm
T, oC
MSN-29 SECOND HEATING
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T, oC
MSN-29 SECOND COOLING
Table 3– Measurements results
Figure 3-6 – some of 4-probes results and its Arrhenius plots for MSN-29
Figure 7 – Measurements results
• From SEM results we can see that with increasing nitrogen concentration, the
grain size escalates, and the oxidation level decreases.
• Conductivity increases with temperature, which indicates the characteristics
of semiconductors. The resistivity, as well as deformation, decreased with
increasing amounts of nitrogen.
• The main charge carriers of samples MSN30-31 are holes, for samples №32-
39 electrons. Contacts placed samples help to perform better conductivity.
• The market analysis indicates the growing popularity and importance of new
developments in solar energy, and solar energy is expected to become the
most prominent power source by 2050.
Figure 8 – Price on the resistance of semiconductor
materials (based on GRANTA 2020) [7]
Figure 9 – The price changes of Mg, Sn
comparing to Ga from 2000 to 2016 [6]
Figure 10 – Recent trends in the use of solar
energy [2]
Figure 11 – Trends in the development of patents for
renewable energy sources [2]
CONCLUSIONS
• The choice of nitride-based alloys in comparison
with other semiconductor materials is
substantiated.
• Magnetron sputtering was chosen as the most
profitable method to achieve good quality
samples.
ELECTRICAL PROPERTIES MEASUREMENTS
In semiconductors at room temperature, the size of the bandgap decreases, the material receives enough thermal energy so that the electrons can
easily jump over the bandgap and make transitions to the conduction band. By performing the 4-point-probe method of measuring electrical
characteristics the resistance and resistivity from there respectively of the sample can be calculated.
Calculated for rectangular samples with different thickness correction factor C = 4.2209. Graphs were transferred to Arrhenius plot in order to
calculate activation energy. For MSN29 Ea=0.06-0.19eV, for MSN30 Ea= 0.063-0.135eV, for MSN31 Ea=0.067-0.083 eV, depending on temperature.
ZnSnN2 = InGaN
MgSnN2 = GaN
ZnSnN2
MgSnN2
GROUP OF MATERIALS AND ASSUMPTION
Unlike monocrystalline and polycrystalline solar panels, thin
films сan be made of various materials, also in a form of
alloys – a promising structure for use in PV due to unique
characteristics and a large selection of components.
Theoretical
direct bandgap
3.43eV
lattice constants:
a = 6.905Å,
b = 5.932Å,
c = 5.499Å
Experimental #1 [5]
direct bandgap
2.57 eV - 3.325 eV,
lattice constants:
a = 5.746-5.932Å,
b = 6.712-6.905Å,
c = 5.313-5.499Å
Experimental #2 [6]
direct bandgap
2.3 eV,
lattice constant
a=4.4832Å
MOCVD MSE MBE
CVD PVD PVD
Toxic elements, require experience Metals and inert gases Metals and inert gases
Up to atmospheric pressure Ultra-high vacuum Ultra-high vacuum
Close to thermodynamic
equilibrium
Can grow thermodynamically
forbidden materials
Can grow thermodynamically
forbidden materials
Thickness can be few nanometers Can cover sharp interfaces Can cover sharp interfaces,
monolayer thickness
Suitable for mass production Suitable for large-scale production Limited for lab research
The high temperature required
(>1000 oC)
T up to 700 oC, possible to grow
high-quality film in room T
T up to 800 oC
Table 1– Comparison of described in literature growth methods for MgSnN2
REFERENCES
[1] F. Alnjiman, “Chemical environment and functional properties of highly crystalline ZnSnN2 thin films deposited by reactive sputtering at
room temperature,” Solar Energy Materials and Solar Cells 182, 30–36, 2018. DOI: 10.1016/j.solmat.2018.02.037
[2] F. Kawamura, "Synthesis of a Novel Rocksalt-Type Ternary Nitride Semiconductor MgSnN," EurJic: European Journal of Inorganic
Chemistry, pp. 446-451, 2020.
[3] K. R. York, "MgSnN2: A New Eco-Friendly Wide Band Gap Semiconductor," Western Michigan University, 2018.
[4] J.F. Pierson, “Materials Characterization,” Course lectures FICM 3A – Multiscale Materials, Lorraine University, 2020
[5] M. Cornils, "How to Extract the Sheet Resistance and Hall Mobility From Arbitrarily Shaped Planar Four-Terminal Devices With Extended
Contacts," IEEE Transactions on Electron Devices, vol. 57, pp. 2087 - 2097, 12 July 2010.
[6] U. S. Geological Survey, “MINERAL COMMODITY SUMMARIES 2017,” 2017.
DOI: 10.3133/70180197
[7] CES Edupack 2016. Cambridge: Granta, 2017
[8] IRENA, "IRENA - International Renewable Energy Agency," 2005-2020. [Online].
Figure 1.2 – Surface pictures MSN-34 Figure 1.3 – Surface pictures MSN-39
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lnR
1/T , K^-1
MSN-29 FIRST HEATING
7.00
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9.00
ln
R
1/T , K^-1
MSN-29 FIRST COOLING
8.40
8.60
8.80
9.00
9.20
9.40
lnR
1/T, K^-1
MSN-29 SECOND HEATING
8.30
8.40
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lnR
1/T, K^-1
MSN-29 SECOND COOLING
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Ohm
T, oC
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