Mg2Si
Material: Magnesium Silicide (Mg2Si)
Section titled “Material: Magnesium Silicide (Mg2Si)”Basic Info
Magnesium silicide is a compound that is dark blue or slightly purple in color. When crystallized, Mg2Si displays a face-centered cubic lattice arrangement. This arrangement possesses the antifluorite structure. Mg2Si is used as an additive for aluminum alloys, as a negative electrode material for lithium-ion batteries, and in photovoltaic applications due to its semiconducting properties.
PV Applications
Section titled “PV Applications”Magnesium silicide is primarily only used in thin film applications due to its difficulties in crystal growth. The low condensation coefficient of magnesium and the barrier behavior of Mg2Si make it difficult to grow Mg2Si of substantial thickness. Successful methods used to produce magnesium silicide films include: molecular-beam epitaxy, solid-phase growth, and ion-beam synthesis.
Basic Parameters at 300 K
Section titled “Basic Parameters at 300 K”Crystal structure: Antifluorite [1]
Debye temperature: 417 K T = 300 K [1]
Density: 1.88 g cm-3 [1]
Dielectric constants: ɛ(0) 20 [1]
ɛ(∞) 13.3
Effective masses: mn 0.46 m0 [1]
mp 0.87 m0 [1]
Electron affinity: 3.59 eV [5]
Lattice constant: a = 6.338 Å [1]
Band structure and carrier concentration
Section titled “Band structure and carrier concentration”Band Structure and carrier concentration
Section titled “Band Structure and carrier concentration”
Information on band structure may be found in Madelung, O. (2004). Semiconductors: Data handbook. (3rd ed., pp. 1595-1605). Springer. [1]
Temperature Dependences
Section titled “Temperature Dependences”
Graph of electrical conductivity vs. temperature for three n-type samples in the range of mixed conduction may be found in Madelung, O. (2004). Semiconductors: Data handbook. (3rd ed., pp. 1595-1605). Springer. [1].
Graph of thermal conductivity vs. temperature for Mg2Si, Mg2Ge and Mg2Sn may be found in Madelung, O. (2004). Semiconductors: Data handbook. (3rd ed., pp. 1595-1605). Springer.b [1].
Energy Gap Narrowing at High Doping Levels
Section titled “Energy Gap Narrowing at High Doping Levels”Effective Masses and Density of States
Section titled “Effective Masses and Density of States”Donors and Acceptors
Section titled “Donors and Acceptors”Donors: Bi [3]
Impurity formation energy data may be found in Zwolenski, P., Tobola, J., Kaprzyk, S., A theoretical sarch for efficient dopants in Mg2X ( X = Si, Ge, Sn) Thermoelectrical materials. Springer Boston, Volume 40, Issure 5, 1 May 2011, Pages 889-897, ISSN 0361-5235, 10.1007/s11664-011-1624-y. [4]
Electrical Properties
Section titled “Electrical Properties”Basic Parameters of Electrical Properties
Section titled “Basic Parameters of Electrical Properties”Energy gap: 0.77 eV Indirect [7]
Conduction type: n-type [3]
Energy spin-orbital splitting: 0.03 eV [6]
Intrinsic carrier concentration: ni = 1*1014 cm-3 T= 300 K [1]
Electron Carrier mobility: 370 cm2/V s [7]
Hole mobility 70 cm2/V s [7]
Mobility and Hall Effect
Section titled “Mobility and Hall Effect”
Graph of Mg2Si hall mobility vs. temperature may be found in Madelung, O. (2004). Semiconductors: Data handbook. (3rd ed., pp. 1595-1605). Springer [1].
Optical properties
Section titled “Optical properties”Refractive index 3.591 [2]
Thermal properties
Section titled “Thermal properties”Lattice heat capacity: Cv = 67.87 J mol-1 K-1 T= 300 K [1]
Mechanical properties, elastic constants, lattice vibrations
Section titled “Mechanical properties, elastic constants, lattice vibrations”Basic Parameters
Section titled “Basic Parameters”Density: 1.88 g cm-3 [1]
Elastic Constants
Section titled “Elastic Constants”Elastic Constants:
c11 12.1(2)*1011 dyn cm-2 T=300 K [1]
c12 2.2(2)*1011 dyn cm-2
c44 4.64(5)*1011 dyn cm-2
Graph of Mg2Si elastic moduli vs. temperature calculated from sound velocity data can be found in Madelung, O. (2004). Semiconductors: Data handbook. (3rd ed., pp. 1595-1605). Springer. [1]
Acoustic Wave Speeds
Section titled “Acoustic Wave Speeds”Sound velocities:
νLA 7.68*105 cm s-1 T= 300 K [110] -direction [1]
νTA,I 4.83*105 cm s-1 [110] -direction, lower branch
νTA,II 4.97*105 cm s-1 [110] -direction, upper branch
νLA 7.65*105 cm s-1 [111] –direction
νTA 4.95*105 cm s-1 [111] -direction
Phonon Frequencies
Section titled “Phonon Frequencies”
νTO(Г15) 8.0*1012s-1 T=300 K [1]
νLO(Г15) 9.8*1012s-1
10.56*1012s-1 T= 77 K
ν(Г25’) 7.75*1012s-1 T=300 K
7.86*1012s-1 T=77 K
References
Section titled “References”
[1] Madelung, O. (2004). Semiconductors: Data handbook. (3rd ed., pp. 1595-1605). Springer.
[2] Benhelal, O., Chahed, A., Laksari, S., Abbar, B., Bouhafs, B. and Aourag, H. (2005), First-principles calculations of the structural, electronic and optical properties of IIA–IV antifluorite compounds. Phys. Status Solidi B, 242: 2022–2032. doi: 10.1002/pssb.200540063
(http://onlinelibrary.wiley.com/doi/10.1002/pssb.200540063/abstract)
[3] Jun-ichi Tani, Hiroyasu Kido, Thermoelectric properties of Bi-doped Mg2Si semiconductors, Physica B: Condensed Matter, Volume 364, Issues 1–4, 15 July 2005, Pages 218-224, ISSN 0921-4526, 10.1016/j.physb.2005.04.017.
(http://www.sciencedirect.com/science/article/pii/S092145260500709X)
[4] Zwolenski, P., Tobola, J., Kaprzyk, S., A theoretical search for efficient dopants in Mg2X ( X = Si, Ge, Sn) Thermoelectrical materials. Springer Boston, Volume 40, Issue 5, 1 May 2011, Pages 889-897, ISSN 0361-5235, 10.1007/s11664-011-1624-y.
(http://dx.doi.org/10.1007/s11664-011-1624-y)
[5] A. Atanassov, M. Baleva, On the band diagram of Mg2Si/Si heterojunction as deduced from optical constants dispersions, Thin Solid Films, Volume 515, Issue 5, 22 January 2007, Pages 3046-3051, ISSN 0040-6090, 10.1016/j.tsf.2006.08.015.
(http://www.sciencedirect.com/science/article/pii/S0040609006010054)
[6] F. Vazquez*, Richard A. Forman, and Manuel Cardona. Electroreflectance Measurements on Mg2Si, Mg2Ge, and Mg2Sn. Department of Physics, Brown University, Providence, Rhode Island 02912. 10.1103/PhysRev.176.905
(http://prola.aps.org/abstract/PR/v176/i3/p905_1)
[7] Yoji Imai, Akio Watanabe, Masakazu Mukaida, Electronic structures of semiconducting alkaline-earth metal silicides, Journal of Alloys and Compounds, Volume 358, Issues 1–2, 25 August 2003, Pages 257-263, ISSN 0925-8388, 10.1016/S0925-8388(03)00037-9.
(http://www.sciencedirect.com/science/article/pii/S0925838803000379)
The development of these pages on photovoltaic materials’ properties was carried out at the University of Utah primarily by undergraduate students Jeff Provost and Carina Hahn working with Prof. Mike Scarpulla. Caitlin Arndt, Christian Robert, Katie Furse, Jash Sayani, and Liz Lund also contributed. The work was fully supported by the US National Science Foundation under the Materials World Network program award 1008302. These pages are a work in progress and we solicit input from knowledgeable parties around the world for more accurate or additional information. Contact earthabundantpv@eng.utah.edu with such suggestions. Neither the University of Utah nor the NSF guarantee the accuracy of these values.
