The diamond-like cubic silicon (d-Si) is widely used in modern electronics and solar cell industries. However, it is not an optimal candidate for thermoelectric application due to its high lattice thermal conductivity. Si (oP32) is a recently predicted orthorhombic silicon allotrope, whose total energy is close to that of d-Si. Using first-principles calculations and Boltzmann transport theory, we systematically investigate the thermoelectric properties of Si (oP32). The lower phonon thermal conductivity and higher power factor are obtained in Si (oP32) than those in diamond silicon. The low phonon thermal conductivity (33.77 W/mK at 300 K) is mainly due to the reduction of the phonon group velocity and enhancement of phonon–phonon scattering (including scattering phase space and strength). Meanwhile, the results also show that the thermoelectric performance along the zz lattice direction is better than that along the xx and yy lattice directions, and the figure of merit (700 K) along the zz lattice direction could approach to 2.45 and 1.75 for p-type and n-type Si (oP32), respectively. The values are much higher than those of d-Si (about 0.06)) and Si24 (0.6), indicating that the Si (oP32) is a promising candidate for thermoelectric applications. Our theoretical studies shed light on the thermoelectric properties of Si (oP32) and could stimulate further experimental studies.
Received: 05 May 2020
Revised: 29 June 2020
Accepted manuscript online: 06 July 2020
Fund: the Program for Changjiang Scholars and Innovative Research Team in University, China (Grant No. IRT13093), the National Natural Science Foundation of China (Grant Nos. 11304262 and 11404275), the Scientific Research Fund of Hunan Provincial Education Department, China (Grant Nos. 17B252, 17K086, and 16K084), the Natural Science Foundation of Hunan Province, China (Grant No. 2016JJ3118), and the Xiangtan University Innovation Foundation for Postgraduate, Hunan Province, China (Grant No. XDCX2020B095).
Pei Zhang(张培), Tao Ouyang(欧阳滔), Chao Tang(唐超), Chao-Yu He(何朝宇), Jin Li(李金), Chun-Xiao Zhang(张春小), and Jian-Xin Zhong(钟建新) Thermoelectric properties of orthorhombic silicon allotrope Si (oP32) from first-principles calculations 2020 Chin. Phys. B 29 118401
Fig. 1.
(a) Crystal structure of Si (oP32), (b) electronic band structure, and (c) electronic density of states (DOS) of Si (oP32). The special point coordinates in Brillouin zone are G (0, 0, 0), X (0.5, 0, 0), S (0.5, 0.5, 0), Y (0, 0.5, 0), G (0, 0, 0), Z (0, 0, 0.5), U (0.5, 0, 0.5), R (0.5, 0.5, 0.5), T (0, 0.5, 0.5), and Z (0, 0, 0.5).
Fig. 2.
(a) Phonon dispersion along different high-symmetry paths and (b) phonon density of states (PDOS) of Si (oP32).
Fig. 3.
(a) Calculated lattice thermal conductivity with respect to temperature for Si (oP32) and d-Si. (b) Lattice thermal conductivity of Si (oP32) and d-Si at 300 K and inset shows the anisotropic factor (| κα – κave |/κave, α = xx, yy, zz).
Fig. 4.
(a) Group velocity, (b)phonon relaxation time, (c) Grüneisen parameter, and (d) three-phonon scattering phase space of Si (oP32) and d-Si versus frequency at room temperature.
Carrier type
El/eV
C3D/(eV/A3)
m*/me
μ/cm2⋅V–1⋅s−1
τ/10–13 s
Electron (xx)
–8.54
0.876
0.836
327.06
1.56
Hole (xx)
–5.65
2.685
40.41
0.617
Electron (yy)
–10.30
0.930
0.221
6643.20
8.35
Hole (yy)
–8.69
0.660
605.53
2.23
Electron (zz)
–6.23
1.066
0.437
3785.53
9.40
Hole (zz)
–17.21
0.139
8693.76
6.87
Table 1.
Values of DP constant E1, elastic constant C3D, effective mass m*, carrier mobility μ, and scattering time τ for electrons and holes along three directions in Si (oP32) at 300 K.
Fig. 5.
Plots of [(a)–(c)] electrical conductivity, [(e)–(f)] Seebeck coefficient, [(g)–(i))] power factor, and [(j)–(l))] electronic thermal conductivity versus chemical potential at different temperatures along xx (left panels), yy (middle panels) and zz (right panels) directions.
Fig. 6.
Plots of thermoelectric figure of merit (ZT) versus chemical potential along (a) xx, (b) yy, and (c) zz (c) lattice directions of Si (oP32) at different temperatures.
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