Semiconductor nanocrystal heterostructures

• US 20070152236A1
• Filed: 12/29/2005
• Published: 07/05/2007
• Est. Priority Date: 12/29/2005
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Bawendi, Moungi, Halpert, Jonathan
• Granted Patent: US 7,394,094 B2
• Time in Patent Office: Days
• US Class Current: 257/183
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C30B 29/60 characterised by shape
• CPC Class Codes: H01L 21/02439 Materials
• CPC Class Codes: H01L 21/02521 Materials
• CPC Class Codes: H01L 21/02603 Nanowires
• CPC Class Codes: H01L 21/0262 Reduction or decomposition of gaseous compounds, e.g. CVD
• CPC Class Codes: H01L 21/02636 Selective deposition, e.g. simultaneous growth of mono- and non-monocrystalline semiconductor materials
• CPC Class Codes: H01L 29/0665 the shape of the body defining a nanostructure nanotechnology per se B82B
• CPC Class Codes: H01L 29/0673 oriented parallel to a substrate
• CPC Class Codes: H01L 29/165 in different semiconductor regions , e.g. heterojunctions
• CPC Class Codes: H01L 29/205 in different semiconductor regions , e.g. heterojunctions
• CPC Class Codes: H01L 29/225 in different semiconductor regions , e.g. heterojunctions
• CPC Class Codes: H01L 29/267 in different semiconductor regions , e.g. heterojunctions H01L29/263 takes precedence

Abstract

A semiconductor nanocrystal can have a barbell shape. The nanocrystal can include two semiconductor materials selected so that upon excitation, one charge carrier is substantially confined to the one semiconductor material and the other charge carrier is substantially confined to the other semiconductor material.

Claims

1. A semiconductor nanocrystal comprising:

a central region and a first end, the central region including a first semiconductor material; and

a distal region at the first end of the rod, the distal region including a second semiconductor material, wherein the first semiconductor material and the second semiconductor material are selected so that, upon excitation, one charge carrier is substantially confined to the central region and the other charge carrier is substantially confined to the distal region.

2. The nanocrystal of claim 1, further comprising a second distal region at a second end of the central region.

3. The nanocrystal of claim 2, wherein the central region is rod-shaped.

4. The nanocrystal of claim 3, wherein the distal regions are each approximately spherical.

5. The nanocrystal of claim 3, wherein the distal regions are each rod-shaped.

6. The nanocrystal of claim 3, wherein the nanocrystal has a length ratio of between 0.1 and 0.95.

7. The nanocrystal of claim 3, wherein the nanocrystal has a length ratio of between 0.2 and 0.9.

8. The nanocrystal of claim 3, wherein the nanocrystal has a radius ratio of between 0.1 and 10.

9. The nanocrystal of claim 3, wherein the nanocrystal has a radius ratio of between 0.3 and 3.5.

10. The nanocrystal of claim 1, wherein the first semiconductor material is a Group II-VI compound, a Group II-V compound, a Group III-VI compound, a Group III-V compound, a Group IV-VI compound, a Group I-III-VI compound, a Group II-IV-VI compound, or a Group II-IV-V compound.

11. The nanocrystal of claim 10, wherein the first semiconductor material is ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgO, MgS, MgSe, MgTe, HgO, HgS, HgSe, HgTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, TlN, TlP, TlAs, TlSb, TlSb, PbS, PbSe, PbTe, or a mixture thereof.

12. The nanocrystal of claim 1, wherein the second semiconductor material is a Group II-VI compound, a Group II-V compound, a Group III-VI compound, a Group Ill-V compound, a Group IV-VI compound, a Group I-III-VI compound, a Group II-IV-VI compound, or a Group II-IV-V compound.

13. The nanocrystal of claim 12, wherein the second semiconductor material is ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgO, MgS, MgSe, MgTe, HgO, HgS, HgSe, HgTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, TlN, TlP, TlAs, TlSb, TlSb, PbS, PbSe, PbTe, or a mixture thereof.

14. A method of making a nanocrystal, comprising:

forming a semiconductor nanocrystal having a central region and a first end, the central region including a first semiconductor material; and

heating a mixture including a coordinating solvent, the semiconductor nanocrystal, an M donor, and an X donor at a temperature sufficient to cap the first end with a second semiconductor material, thereby forming a capped semiconductor nanocrystal having a central region including the first semiconductor material and a distal region including the second semiconductor material, wherein the first semiconductor material and the second semiconductor material are selected so that, upon excitation, one charge carrier is substantially confined to the central region and the other charge carrier is substantially confined to the distal region.

15. The method of claim 14, further comprising contacting the semiconductor nanocrystal with an etching agent before heating the mixture.

16. The method of claim 14, wherein the semiconductor nanocrystal further includes a second end.

17. The method of claim 16, wherein heating the mixture further caps the second end with the second semiconductor material.

18. The method of claim 17, wherein the central region is rod-shaped.

19. The method of claim 17, further comprising selecting a coordinating solvent and a temperature to influence a shape of a distal region.

20. The method of claim 19, wherein the coordinating solvent and the temperature are selected to form an approximately spherical distal region.

21. The method of claim 18, wherein the distal regions are each approximately spherical.

22. The method of claim 18, wherein the distal regions are each rod-shaped.

23. The method of claim 17, wherein the capped nanocrystal has a length ratio of between 0.1 and 0.95.

24. The method of claim 17, wherein the capped nanocrystal has a length ratio of between 0.2 and 0.9.

25. The method of claim 17, wherein the capped nanocrystal has a radius ratio of between 0.1 and 10.

26. The method of claim 17, wherein the nanocrystal has a radius ratio of between 0.3 and 3.5.

27. The method of claim 14, wherein the first semiconductor material is a Group II-VI compound, a Group II-V compound, a Group III-VI compound, a Group Ill-V compound, a Group IV-VI compound, a Group I-III-VI compound, a Group II-IV-VI compound, or a Group II-IV-V compound.

28. The method of claim 27, wherein the first semiconductor material is ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgO, MgS, MgSe, MgTe, HgO, HgS, HgSe, HgTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, TlN, TlP, TlAs, TlSb, TlSb, PbS, PbSe, PbTe, or a mixture thereof.

29. The method of claim 14, wherein the second semiconductor material is a Group II-VI compound, a Group II-V compound, a Group III-VI compound, a Group Ill-V compound, a Group IV-VI compound, a Group I-III-VI compound, a Group II-IV-VI compound, or a Group II-IV-V compound.

30. The method of claim 29, wherein the second semiconductor material is ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgO, MgS, MgSe, MgTe, HgO, HgS, HgSe, HgTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, TlN, TlP, TlAs, TlSb, TlSb, PbS, PbSe, PbTe, or a mixture thereof.

31. A photovoltaic device comprising:

a first electrode;

a second electrode;

a voltage source configured to apply a voltage across the first electrode and the second electrode; and

an active layer in electrical communication with the first electrode and the second electrode, wherein the active layer includes a population of semiconductor nanocrystals each having a central region and a first end, the central region including a first semiconductor material, and a distal region at the first end of the rod, the distal region including a second semiconductor material, wherein the first semiconductor material and the second semiconductor material are selected so that, upon excitation, one charge carrier is substantially confined to the central region and the other charge carrier is substantially confined to the distal region.

32. The device of claim 31, wherein the population of semiconductor nanocrystals are substantially aligned.

33. The device of claim 32, wherein the first electrode and the second electrode are parallel.

34. The device of claim 33, wherein the population of semiconductor nanocrystals are substantially aligned with an alignment direction substantially perpendicular to the first electrode and the second electrode.

35. The device of claim 31, wherein the nanocrystal further includes a second distal region at a second end of the central region.

36. The device of claim 35, wherein the central region is rod-shaped.

37. The device of claim 36, wherein the distal regions are each approximately spherical.

38. The device of claim 36, wherein the distal regions are each rod-shaped.

39. The device of claim 36, wherein the nanocrystal has a length ratio of between 0.1 and 0.95.

40. The device of claim 36, wherein the nanocrystal has a length ratio of between 0.2 and 0.9.

41. The device of claim 36, wherein the nanocrystal has a radius ratio of between 0.1 and 10.

42. The device of claim 36, wherein the nanocrystal has a radius ratio of between 0.3 and 3.5.

43. The device of claim 31, wherein the first semiconductor material is a Group II-VI compound, a Group II-V compound, a Group III-VI compound, a Group III-V compound, a Group IV-VI compound, a Group I-III-VI compound, a Group II-IV-VI compound, or a Group II-IV-V compound.

44. The device of claim 43, wherein the first semiconductor material is ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgO, MgS, MgSe, MgTe, HgO, HgS, HgSe, HgTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, TlN, TlP, TlAs, TlSb, TlSb, PbS, PbSe, PbTe, or a mixture thereof.

45. The device of claim 31, wherein the second semiconductor material is a Group II-VI compound, a Group II-V compound, a Group III-VI compound, a Group III-V compound, a Group IV-VI compound, a Group I-III-VI compound, a Group II-IV-VI compound, or a Group II-IV-V compound.

46. The device of claim 45, wherein the second semiconductor material is ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgO, MgS, MgSe, MgTe, HgO, HgS, HgSe, HgTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, TlN, TlP, TlAs, TlSb, TlSb, PbS, PbSe, PbTe, or a mixture thereof.