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 method of improving thermoelectric efficiency of a silicon nanowire, comprising:
providing a silicon nanowire consisting substantially of crystalline silicon;
selecting a thermal conductivity of the silicon nanowire by controlling a diameter of the silicon nanowire within a range of ten to twenty nanometers and controlling a length of the silicon nanowire to be at least four times the diameter of the silicon nanowire without substantially changing an electrical conductivity of the silicon nanowire; and
selecting a thermoelectric power of the silicon nanowire by controlling the doping concentration of the silicon nanowire within a range of 3×10 19 cm −3 and 2×10 20 cm −3 ,
such that the silicon nanowire has a thermoelectric efficiency at least one hundred times greater than a thermoelectric efficiency of bulk silicon,
wherein the silicon nanowire is doped p-type or n-type, but not both, and
wherein the thermoelectric efficiency of the silicon nanowire is greater than or equal to about 0.31 over a temperature range from about 100K to 200K.
2. The method of claim 1 , wherein the thermoelectric power is controlled, at least in part, by phonon drag.
3. The method of claim 2 , wherein phonon drag contribution to thermoelectric power is a function of silicon nanowire doping.
4. The method of claim 1 , wherein selecting the thermal conductivity of the silicon nanowire and selecting the thermoelectric power of the silicon nanowire is for power generation.
5. The method of claim 4 , wherein the power generation is based on Seebeck effect.
6. The method of claim 1 , wherein selecting the thermal conductivity of the silicon nanowire and selecting the thermoelectric power of the silicon nanowire is for refrigeration.
7. The method of claim 6 , wherein the refrigeration is based on Peltier effect.
8. The method of claim 1 , wherein the silicon nanowire is 20 nm wide and p-type doped at a concentration of 7×10 19 cm −3 .
9. The method of claim 1 , wherein the silicon nanowire is fabricated by a Superlattice Nanowire Pattern transfer process.
10. The method of claim 1 , wherein the thermoelectric efficiency of the silicon nanowire is maximal at a temperature of about 200K.