Mg2Si

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

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

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 m                                             [1]

Electron affinity:                                                                  3.59 eV                                                 [5]

Lattice constant:                                                          a = 6.338 Å                                                 [1]                                                    

Band structure and carrier concentration

        Band Structure and carrier concentration

 

Informatoin on band structure may be found in Madelung, O. (2004). Semiconductors: Data handbook. (3rd ed., pp. 1595-1605). Springer. [1]

 

       

 

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

        Effective Masses and Density of States

        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

        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

               

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

Refractive index                                        3.591                                                                                     [2]

Thermal properties

Lattic heat capacity:                        Cv = 67.87 J mol-1 K-1            T= 300 K                                     [1]

Mechanical properties, elastic constants, lattice vibrations

        Basic Parameters                                                

Density:                                        1.88 g cm-3                                                                      [1]

  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

                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

 

                νTO15)                 8.0*1012s-1           T=300 K                                                [1]

                νLO15)                 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

 

[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 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.

(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.