Semiconductor nanowire thermoelectric materials and devices, and processes for producing same
The present invention provides nanowires and nanoribbons that are well suited for use in thermoelectric applications. The nanowires and nanoribbons are characterized by a periodic compositional longitudinal modulation. The nanowires are constructed using lithographic techniques from thin semiconductor membranes, or “nanomembranes.”
1. A nanowire comprising a plurality of alternating semiconductor nanowire segments having a first composition and semiconductor nanowire segments having a second composition that is different from the first composition, each semiconductor nanowire segment having a side surface extending in a direction along the longitudinal axis of the semiconductor nanowire segment, and an end which includes a portion of the side surface, wherein the ends of neighboring nanowire segments overlap in that the ends of the semiconductor nanowire segments having the first composition are disposed over and are bonded to the ends of their neighboring nanowire segments having the second composition, such that a plurality of junctions, formed by the interfaces between the side surfaces of neighboring nanowire segments at the areas of overlap and connected in series, are provided along the nanowire.
2. The nanowire of claim 1 , wherein the nanowire has a zig-zag structure along its length with the junctions formed at the bends in the zig-zag structure.
3. The nanowire of claim 1 having cross-sectional dimensions of no greater than about 100 nm×100 nm.
4. The nanowire of claim 1 having cross-sectional dimensions of no greater than about 30 nm×30 nm.
5. The nanowire of claim 1 , wherein the angle between the longitudinal axes of the nanowire segments having the first composition and the longitudinal axes of the nanowire segments having the second composition is less than 180° and greater than 0°.
6. The nanowire of claim 5 , wherein the angle between the longitudinal axes of the nanowire segments having the first composition and the longitudinal axes of the nanowire segments having the second composition is from about 10° to 170°.
7. The nanowire of claim 1 , wherein the first composition comprises a p-type semiconductor material and the second composition comprises an n-type semiconductor material.
8. The nanowire of claim 1 , wherein the first composition comprises a first SiGe alloy and the second composition comprises a second SiGe alloy.
9. A thermoelectric material comprising a plurality of the nanowires of claim 1 .
10. The thermoelectric material of claim 9 , wherein the nanowires are aligned in a linear array.
11. A thermoelectric device incorporating the thermoelectric material of claim 9 .
12. A method of making the nanowire of claim 5 , the method comprising:
(a) forming a first set of strips comprising a first semiconductor material, wherein the strips are separated by lateral channels;
(b) forming a second set of strips comprising a second semiconductor material, wherein the strips are separated by lateral channels;
(c) transferring and bonding the second set of strips to the first set of strips at an orientation that provides an angle of greater than zero and less than 180° between the longitudinal axes of the first set of strips and the longitudinal axes of the second set of strips to provide a grid structure comprising an array of junctions; and
(d) slicing the grid structure diagonally through adjacent rows of junctions, whereby the nanowire of claim 5 is formed.
13. The method of claim 12 , wherein the step of slicing through adjacent rows of junctions comprises slicing through the junctions at an angle that bisects the angles between the longitudinal axes of the first set of strips and the longitudinal axes of the second set of strips.
14. The method of claim 12 , wherein the first set of strips is transferred and bonded to the second set of strips at an orientation that provides an angle of about 90° between the longitudinal axes of the first set of strips and the longitudinal axes of the second set of strips.
15. The method of claim 14 , wherein the step of slicing through adjacent rows of junctions comprises slicing through the junctions at an angle that bisects the angles between the longitudinal axes of the first set of strips and the longitudinal axes of the second set of strips.
16. The nanowire of claim 1 , wherein the junctions are pn-junctions.
17. The nanowire of claim 1 , wherein the nanowire has cross-sectional dimensions of no greater than about 50 nm.
18. The thermoelectric material of claim 10 comprising thousands of the nanowires.
19. The nanowire of claim 1 , wherein neighboring nanowire segments are not coaxial and not coplanar.