Methods and devices for controlling thermal conductivity and thermoelectric power of semiconductor nanowires
Methods and devices for controlling thermal conductivity and thermoelectric power of semiconductor nanowires are described. The thermal conductivity and the thermoelectric power are controlled substantially independently of the electrical conductivity of the nanowires by controlling dimensions and doping, respectively, of the nanowires. A thermoelectric device comprising p-doped and n-doped semiconductor nanowire thermocouples is also shown, together with a method to fabricate alternately p-doped and n-doped arrays of silicon nanowires.
1. A thermoelectric device, comprising:
a nanowire array comprising an individual nanowire consisting essentially of doped silicon, wherein the individual nanowire comprises a semiconductor, and wherein the individual nanowire has a diameter up to about 20 nanometers (nm) and a length that is at least about 4 times the diameter of the individual nanowire,
wherein the individual nanowire is doped p-type or n-type, but not both, and has a doping concentration from about 3×10 19 cm −3 to 2×10 20 cm −3 , and
wherein the individual nanowire has a thermoelectric efficiency that is at least one hundred times greater than a thermoelectric efficiency of bulk silicon, wherein the thermoelectric efficiency of the individual nanowire is greater than or equal to about 0.31 over a temperature range from about 100 K to 200 K.
2. The thermoelectric device of claim 1 , wherein the individual nanowire is about 20 nm wide and p-type doped at a concentration of about 7×10 19 cm −3 .
3. The thermoelectric device of claim 2 , wherein an electric conductivity of the individual nanowire changes less than 1,000 Ω −1 cm −1 across a temperature range of 50K to 200K.
4. The thermoelectric device of claim 1 , wherein the individual nanowire is about 20 nm wide and p-type doped at a concentration of about 1.3×10 20 cm −3 .
5. The thermoelectric device of claim 4 , wherein an electric conductivity of the individual nanowire changes less than 1,000 Ω −1 cm −1 across a temperature range of 50K to 200K.
6. The thermoelectric device of claim 1 , wherein the thermoelectric efficiency of the individual nanowire is maximal at a temperature of about 200 K.
7. The thermoelectric device of claim 1 , wherein the diameter is from about 10 nm to 20 nm.
8. The thermoelectric device of claim 1 , further comprising electric contacts in electrical communication with the nanowire array.
9. The thermoelectric device of claim 8 , wherein the electrical contacts include platinum.
10. The thermoelectric device of claim 8 , wherein the electrical contacts include titanium.
11. The thermoelectric device of claim 1 , wherein the nanowire array comprises a plurality of individual nanowires.
12. The thermoelectric device of claim 11 , wherein the plurality of individual nanowires comprises one or more p-type elements alternately connected to one or more n-type elements.
13. The thermoelectric device of claim 11 , wherein the plurality of individual nanowires are connected electrically in series.
14. The thermoelectric device of claim 11 , wherein the plurality of individual nanowires are connected in parallel.
15. A thermoelectric device comprising at least one p-doped nanowire array and at least one n-doped nanowire array, wherein the at least one p-doped nanowire array and the at least one n-doped nanowire array being connected electrically in series and thermally in parallel,
wherein at least one nanowire array of the at least one p-doped nanowire array and the at least one n-doped nanowire array each comprises an individual nanowire consisting essentially of doped silicon, wherein the individual nanowire comprises a semiconductor, and wherein the individual nanowire has a diameter up to about 20 nanometers (nm) and a length that is at least about 4 times the diameter of the individual nanowire,
wherein the individual nanowire is doped p-type or n-type, but not both, and has a doping concentration from about 3×10 19 cm′ to 2×10 20 cm −3 , and
wherein the individual nanowire has a thermoelectric efficiency that is at least one hundred times greater than a thermoelectric efficiency of bulk silicon, wherein the thermoelectric efficiency of the individual nanowire is greater than or equal to about 0.31 over a temperature range from about 100 K to 200 K.
16. The thermoelectric device of claim 15 , wherein the at least one p-doped nanowire array comprises a plurality of p-doped semiconductor nanowires and the at least one n-doped nanowire array comprises a plurality of n-doped semiconductor nanowires.
17. The thermoelectric device of claim 16 , wherein the p-doped semiconductor nanowires or the n-doped nanowires have ZT efficiency values above 1, wherein
ZT
=
S
2
σ
κ
T
,
where S is the thermoelectric power of the thermoelectric device,
S
=
dV
dT
,
σ is the electrical conductivity of the thermoelectric device, κ is the thermal conductivity of the thermoelectric device, and T is the temperature of the thermoelectric device.