Electronic Properties of Si Nanowires

1
Electronic Properties of Si Nanowires

• Yun Zheng, 1Cristian Rivas, Roger Lake, Khairul
  Alam, 2Timothy Boykin, and 3Gerhard Klimeck
• Deptartment of Electrical Engineering, University
  of California Riverside
• 1Eric Jonson School of Engineering, University of
  Texas at Dallas
• 2University of Alabama Huntsville
• 3Department of Electrical and Computer
  Engineering, Purdue University

2
Si 100 Nanowire Structure
Unit Cell
H passivated
Si Nanowire on Si substrate
3
Approach

• sp3sd5 empirical tight binding model
• parameters optimized with genetic algorithm
  (Boykin et al., Phys. Rev. B, v. 69, 115201
  (2004).
• 3D discretized effective mass model
• E kz (zeegv)
• Transmission vs. E
• NEGF and RGF T trG1,1 A1,1 - G1,1G1,1G1,1

R
R
R
4
E-kz of 1.54 nm Si Wire
5
Band Gap vs. Wire Thickness
6
X2 X4 Splitting
7
Splitting of X4 States at G

• The lowest state is the reference energy E0 at
  each dimension.

8
Splitting of 3 Highest Valence Bands at G

• The highest state is the reference energy E0 at
  each dimension.

9
Effective Mass at Conduction Band Edge
0.27 m0

• Bulk mt 0.2 m0

10
Effective Mass at Valence Band Edge

• 100 bulk masses mhh 0.28 m0, mlh 0.21 m0,
  and mso 0.25 m0

11
Conduction Band Transmission Full Band and
Single Band
T trG1,1 A1,1 - G1,1G1,1G1,1

• 1.54 nm Si wire.
• Band edges differ by 100 meV.

12
Valence Band Transmission Full Band and Single
Band

• Band edges differ by 18 meV.

1.54 nm wire
13
Transmission of Wire on Si Substrate
14
Conclusion

• Brillouin zone ½ length of bulk Si along D line.
• Conduction band Valley splitting reduces m and
  confinement increases mt of bandedge (34 for
  2.7nm wire).
• m of valence band edge 6x heavier than bulk and
  next highest band even heavier.
• For wires gt 1.54 nm, conduction band edge splits
  into 3 energies. Center energy is 2-fold
  degenerate evenly spaced between lowest and
  highest energy. Band-edge is non-degenerate.