Forming II-VI core-shell semiconductor nanowires
View Patent ↗A method of making II-VI core-shell semiconductor nanowires includes providing a support; depositing a layer including metal alloy nanoparticles on the support; and heating the support and growing II-VI core semiconductor nanowires where the metal alloy nanoparticles act as catalysts and selectively cause localized growth of the core nanowires. The method further includes modifying the growth conditions and shelling the core nanowires to form II-VI core-shell semiconductor nanowires.
1. A method of making II-VI core-shell semiconductor nanowires, comprising:
(a) providing a support;
(b) depositing a layer including metal alloy nanoparticles on the support;
(c) heating the support and flowing II-VI semiconductor precursors to selectively provide localized growth of II-VI core semiconductor nanowires wherein the metal alloy nanoparticles act as catalysts; and
(d) modifying the growth conditions and shelling the core nanowires to form II-VI core-shell semiconductor nanowires by flowing II-VI semiconductor precursors to impinge upon the core semiconductor nanowires and obtain non-selective growth.
2. The method of claim 1 wherein the support is selected to withstand II-VI metal-organic vapor phase epitaxy growth temperatures.
3. The method of claim 2 wherein the support includes glasses, semiconductor substrates, metal foils, or high temperature plastics.
4. The method of claim 1 further including depositing a low energy surface film on the support.
5. The method of claim 4 wherein the low energy surface film includes silicon oxide or aluminum oxide.
6. The method of claim 1 wherein the metal alloy is gold-tin.
7. The method of claim 6 wherein the volume ratio of gold to tin ranges from 1:5 to 5:1.
8. The method of claim 6 wherein step (b) includes thermal evaporation or sputtering of gold and tin.
9. The method of claim 1 wherein the II-VI semiconductor precursors include diethylzinc, dimethyl cadmium, tert-butyl selenide, tert-butyl sulfide, di-isopropyl telluride, or bis(methyl-η 5 -cyclopentadienyl)magnesium.
10. The method of claim 1 wherein step (c) the support is heated between 270° C. and 340° C.
11. The method of claim 1 wherein step (d) the growth conditions are modified by adjusting the precursor flow rates and heating the support to between 270° C. and 340° C.
12. The method of claim 1 wherein step (d) the growth conditions are modified by heating the support to between 350° C. and 390° C.
13. The method of claim 1 wherein the core-shell semiconductor nanowire growth takes place at a pressure between 50 torr and 760 torr.
14. The method of claim 1 wherein step (c) the molar ratio of column VI precursors to column II precursors is in a range from 1:1 to 4:1.
15. The method of claim 1 wherein step (c) further includes at least two column II precursors or at least two column VI precursors or both.
16. The method of claim 1 wherein step (d) the molar ratio of column VI precursors to column II precursors is in a range from 1:1 to 4:1.
17. The method of claim 1 wherein step (d) further includes at least two column II precursors or at least two column VI precursors or both.
18. The method of claim 1 wherein the diameter of each core-shell nanowire is less than 500 nanometers.
19. The method of claim 18 wherein the diameter of each core-shell nanowire is less than 100 nanometers.
20. The method of claim 1 wherein the length of each core-shell nanowire is greater than 500 nanometers.
21. The method of claim 20 wherein the length of each core-shell nanowire is greater than 2 microns.
22. The method of claim 1 wherein step (c) further includes forming the core of each nanowire to include one or more discrete heterostructure units whose II-VI material composition is either uniform or varies over its length.
23. The method of claim 22 includes sequentially delivering II-VI semiconductor precursors to cause these materials to deposit and grow the cores containing one or more discrete heterostructure units.
24. The method of claim 22 wherein the discrete heterostructure units have lengths which range from 1-10 nm to microns.
25. The method of claim 1 wherein dopants are provided in step (c) or (d) or both which modify the conductivity of the core-shell nanowires.
26. The method of claim 1 wherein dopants are provided in step (c) or (d) or both which modify the spectral response of the core-shell nanowires.
27. The method of claim 26 wherein the dopants are selected from Mn or Cu.
28. The method of claim 1 wherein the shell includes a plurality of layers.
29. The method of claim 1 wherein the shell thickness ranges from 1 nanometer to hundreds of nanometers.
30. The method of claim 1 wherein the shell is either uniform or varies over its diameter.