Porous semiconductor and process for producing the same

• US 20050042743A1
• Filed: 07/10/2003
• Published: 02/24/2005
• Est. Priority Date: 07/11/2002
• Status: Active Grant

• Current Assignee: Sumitomo Electric Industries Limited (Sumitomo Corporation)
• Original Assignee: Sumitomo Electric Industries Limited (Sumitomo Corporation)
• Inventors: Tatsumi, Masami, Kawai, Chihiro
• Granted Patent: US 7,468,529 B2
• Time in Patent Office: Days
• US Class Current: 435/287.200
• CPC Class Codes: A61L 9/16 using physical phenomena
• CPC Class Codes: A61L 9/205 using a photocatalyst or photosensitiser
• CPC Class Codes: B01J 35/39 Photocatalytic properties
• CPC Class Codes: C02F 1/001 Processes for the treatment of water whereby the filtration technique is of importance C02F1/44 takes precedence; construction of filters in general B01D24/00 - B01D41/00
• CPC Class Codes: C02F 1/32 with ultraviolet light
• CPC Class Codes: C02F 1/725 by catalytic oxidation
• CPC Class Codes: C02F 2101/30 Organic compounds
• CPC Class Codes: C02F 2303/04 Disinfection
• CPC Class Codes: C09K 11/02 Use of particular materials as binders, particle coatings or suspension media therefor
• CPC Class Codes: C09K 11/0883 Arsenides; Nitrides; Phosphides
• CPC Class Codes: C09K 11/54 containing zinc or cadmium
• CPC Class Codes: C09K 11/59 containing silicon
• CPC Class Codes: C09K 11/62 containing gallium, indium or thallium
• CPC Class Codes: C09K 11/64 containing aluminium
• CPC Class Codes: C09K 11/65 containing carbon in organic compounds C09K11/06
• CPC Class Codes: C09K 11/672 with zinc or cadmium
• CPC Class Codes: C09K 11/77 containing rare earth metals
• CPC Class Codes: C09K 11/7704 Halogenides C09K11/7701 takes precedence
• CPC Class Codes: C09K 11/7766 containing two or more rare earth metals
• CPC Class Codes: C09K 11/7783 containing two or more rare earth metals one of which being europium
• CPC Class Codes: H01L 2924/00 : Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 : Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 33/16 : with a particular crystal structure or orientation, e.g. polycrystalline, amorphous or porous
• CPC Class Codes: H01L 33/18 : within the light emitting region

Abstract

The present invention provides a filter with which organic matter, bacteria, viruses, and other harmful substances can be trapped, and the trapped material can be sterilized and decomposed, at low cost and extremely high efficiency. A porous ceramic or metal is used as a substrate, and a porous semiconductor composed of a semiconductor material having a light emitting function is formed in the interior or on the surface of this substrate. An electrode is provided to this product to serve as a filter, voltage is applied so that ultraviolet light is emitted while a fluid is being filtered, and any harmful substances are filtered and simultaneously sterilized and decomposed. The porous semiconductor layer is preferably composed of columns grown perpendicular to the substrate plane, and has the function of emitting ultraviolet light with a wavelength of 400 nm or less. The pores in the porous substrate column are through-holes perpendicular to the substrate plane, and the average size of these pores is preferably from 0.1 to 100 μm. The distal ends of the columns preferably have a pointed shape. To manufacture, a suspension of semiconductor particles having a light emitting function is filtered through the porous substrate serving as a filter medium so as to form a deposited layer of semiconductor particles on the porous substrate surface. A deposited layer of p-type semiconductor particles and a deposited layer of n-type semiconductor particles may also be formed so that these form a pn junction. Further, the present invention is characterized in that an insulating layer is formed on the top and bottom surfaces of the porous semiconductor layer, and semiconductor particles are dispersed in the insulating layer, with the bandgap of the semiconductor particles in the porous light emitting layer or the porous semiconductor layer being at least 3.2 eV, and being doped with gadolinium, which is the light emitting center.

In addition, the porous semiconductor layer may be made of porous silicon nitride composed of columnar Si₃N₄ particles with an average aspect ratio of at least 3 and an oxide-based binder phase containing at least one of rare earth element, and emit visible light or ultraviolet light.

Claims

1. A porous semiconductor, comprising:

a porous substrate having continuous pores; and

a porous semiconductor layer having a light emitting function that works by electroluminescence, cathode luminescence, or photoluminescence, and having continuous pores.

2. A porous semiconductor according to claim 1, which emits ultraviolet light with a wavelength of 400 nm or less.

3. A porous semiconductor according to claim 2, wherein the ultraviolet light has a wavelength of 200 to 400 nm.

4. A porous semiconductor according to claim 3, wherein the ultraviolet light has a wavelength of 230 to 270 nm.

5. A porous semiconductor according to any of claims 1 to 4, wherein the semiconductor layer has a pn junction structure.

6. A porous semiconductor according to any of claims 1 to 5, wherein a porosity of the semiconductor layer is at least 30%.

7. A porous semiconductor according to any of claims 1 to 6, wherein an average pore size of the porous substrate and/or the porous semiconductor layer is from 0.0003 to 100 fÊ

m.

8. A porous semiconductor according to any of claims 1 to 7, wherein an insulating layer is formed on the front and/or back surface of the semiconductor layer.

9. A porous semiconductor according to any of claims 1 to 8, wherein the insulating layer is formed from a material having a photocatalytic function.

10. A porous semiconductor according to any of claims 1 to 9, wherein the semiconductor layer is made up of crystal particles, and a surface of these crystal particles is coated with particles having a photocatalytic function.

11. A filter composed of the porous semiconductor according to any of claims 1 to 10.

12. A filter according to claim 11, wherein the porous substrate is a porous ceramic or a metal having continuous pores, and a porous semiconductor layer is provided in an interior or on a surface of the substrate.

13. A filter according to claim 12, wherein a porosity of the porous substrate is at least 30%.

14. A filter according to claim 12 or 13, wherein a thickness of the porous semiconductor layer disposed on the surface of the porous substrate is from 1 to 1000 fÊ

m.

15. A filter according to any of claims 12 to 14, wherein an average pore size of the porous substrate is from 0.01 to 1000 fÊ

m.

16. A porous semiconductor according to any of claims 1 to 9, wherein the porous semiconductor layer is composed of numerous columns of semiconductor material erected on a surface of the porous substrate.

17. A porous semiconductor according to claim 16, wherein the pores in the porous substrate are through-holes perpendicular to a substrate plane.

18. A porous semiconductor according to claim 16 or 17, wherein an average pore size of the porous substrate is from 0.1 to 100 fÊ

m.

19. A porous semiconductor according to any of claims 16 to 18, wherein a pn junction is formed in a lengthwise direction of the columns.

20. A porous semiconductor according to any of claims 16 to 19, wherein the columns comprising a base component and a pointed component located on the distal end side of this base component.

21. A porous semiconductor according to any of claims 16 to 20, wherein an electroconductive porous film is disposed as an electrode at the distal ends of the columns and on an opposite surface of the porous substrate from the surface where the columns are formed.

22. A porous semiconductor according to any of claims 16 to 21, wherein an electroconductive porous film is disposed as one electrode at the distal ends of the columns, and the porous substrate is composed of an electroconductive material and constitutes another electrode.

23. A porous semiconductor according to claim 21 or 22, wherein a surface of the columns and/or a column-side surface of the electrode disposed at the distal ends of the columns is coated with particles having a photocatalytic function.

24. A filter that makes use of the porous semiconductor according to any of claims 16 to 23.

25. A porous semiconductor according to any of claims 1 to 10, wherein the porous semiconductor layer is formed by depositing semiconductor particles having a light emitting function on a surface of the porous substrate.

26. A porous semiconductor according to claim 25, comprising an electrode for injecting current into the porous semiconductor layer.

27. A porous semiconductor according to claim 25 or 26, wherein the porous semiconductor layer is composed of a deposited layer of p-type semiconductor particles and a deposited layer of n-type semiconductor particles to form a pn junction.

28. A porous semiconductor according to any of claims 25 to 27, wherein a surface of the semiconductor particles is coated with an insulating layer.

38. A filter composed of the porous semiconductor according to any of claims 25 to 28.

39. A porous semiconductor according to any of claims 1 to 7, wherein an electrode is formed on a top or bottom surface of the porous substrate, a porous insulating layer, a porous semiconductor layer, and a porous insulating layer are laminated on the porous substrate, another electrode is formed on a top surface, the porous semiconductor layer emits ultraviolet light by electroluminescence when AC voltage is applied between the electrodes, and the porous semiconductor has a bandgap of at least 3.2 eV and is doped with gadolinium, which is the light emitting center.

40. A porous semiconductor according to any of claims 1 to 7, wherein an electrode is formed on a top or bottom surface of the porous substrate, the porous semiconductor layer is formed by dispersing semiconductor particles in an insulating layer, an electrode is formed on the porous semiconductor layer, the porous semiconductor layer emits ultraviolet light by electroluminescence when AC voltage is applied between the electrodes, and the semiconductor particles have a bandgap of at least 3.2 eV and are doped with gadolinium, which is the light emitting center.

41. A porous semiconductor according to claim 39 or 40, wherein a surface of the porous insulating layer or of the porous semiconductor layer formed by dispersing semiconductor particles in the insulating layer is covered by a porous layer having a photocatalytic function, or pore walls of the porous substrate are covered by a material having a photocatalytic function.

42. A porous semiconductor according to claim 39 or 41, wherein the porous insulating layer or the insulating layer in which the semiconductor particles are dispersed is formed from a material having a photocatalytic function.

43. A porous semiconductor according to any of claims 39 to 42, wherein the bandgap of the porous semiconductor layer or the semiconductor particles is at least 4.0 eV.

44. A porous semiconductor according to any of claims 39 to 43, wherein either the electrodes are porous or the structure of the electrodes has a porous structure.

45. A porous semiconductor according to claim 44, wherein the electrodes are composed of a porous transparent electroconductive film.

48. A filter composed of the porous semiconductor according to any of claims 39 to 45.

49. A bioreactor composed of the porous semiconductor according to any of claims 39 to 45.

50. An ultraviolet light source that makes use of the porous semiconductor according to any of claims 39 to 45.

51. A porous semiconductor according to any of claims 1 to 9, wherein the porous semiconductor layer is made of porous silicon nitride composed of columnar Si3N4 particles with an average aspect ratio of at least 3 and an oxide-based binder phase containing at least one of rare earth element, and emits visible light or ultraviolet light.

52. A porous semiconductor according to claim 51, wherein a surface of the columnar Si3N4 particles is covered with a film or particles having a photocatalytic function.

53. A porous semiconductor according to claim 51, wherein a film or deposited layer of particles having a photocatalytic function is formed on a surface of the porous semiconductor layer.

54. A porous semiconductor according to any of claims 51 to 53, which emits ultraviolet light having its peak wavelength at 300 to 320 nm.

55. A porous semiconductor according to any of claims 51 to 54, containing at least gadolinium as the rare earth element.

56. A porous semiconductor according to claim 55, further containing yttrium as the rare earth element.

57. A porous semiconductor according to any of claims 51 to 56, wherein an average pore size of the porous semiconductor layer is from 0.1 to 5 fÊ

m.

58. A porous semiconductor according to any of claims 51 to 57, wherein a three-point bending strength is at least 100 MPa.

59. A light emitting device having the porous semiconductor according to any of claims 51 to 58.

60. A filter that makes use of the porous semiconductor according to any of claims 51 to 58.

61. A porous semiconductor according to claim 1, wherein the porous substrate is columnar in shape and has formed therein in an axial direction a plurality of holes serving as passages for a fluid to be treated, the continuous pores lead from an inner wall of the holes to a side of the column, and the porous semiconductor layer is formed on the inner wall.

62. A porous semiconductor according to claim 1, wherein the porous substrate is a honeycomb structure, in the honeycomb structure are formed an inflow-side honeycomb passage and an outflow-side honeycomb passage separated by a partition, the continuous pores are formed inside the partition, and the porous semiconductor layer is formed on the inner walls of the inflow-side honeycomb passage.

29. A method for manufacturing a porous semiconductor having a light emitting function and composed of a porous substrate having through-holes, and a porous semiconductor layer formed on a surface of this substrate, the method comprising at least steps of:

(a) preparing a porous substrate and at least one of semiconductor particles having a light emitting function that works by electroluminescence, cathode luminescence, or photoluminescence;

(b) producing a suspension of the semiconductor particles; and

(c) filtering the suspension through the porous substrate and forming a deposited layer composed of semiconductor particles on the surface of the porous substrate.

30. A method for manufacturing a porous semiconductor according to claim 29, further comprising a step of forming an electrode for injecting current into the deposited layer.

31. A method for manufacturing a porous semiconductor according to claim 29 or 30, further comprising a step of performing a treatment for bonding together the individual semiconductor particles that form the deposited layer, after the step (c).

32. A method for manufacturing a porous semiconductor according to claim 31, wherein the treatment is a heat treatment.

33. A method for manufacturing a porous semiconductor according to claim 31, wherein the treatment is a treatment in which a semiconductor material is deposited in the vapor phase at the contact portions between the semiconductor particles.

34. A method for manufacturing a porous semiconductor according to any of claims 29 to 33, comprising a step of coating a surface of the semiconductor particles with an insulating layer or a material having a photocatalytic function, between the steps (a) and (b).

35. A method for manufacturing a porous semiconductor according to any of claims 29 to 34, wherein a step of coating a porous substrate surface with an insulating layer is added before the step (c), and a step of coating the surface of the deposited layer with an insulating layer is added after the step (c).

36. A method for manufacturing a porous semiconductor according to any of claims 29 to 35, wherein in the step (b), at least one of suspension of p-type semiconductor particles and at least one of suspension of n-type semiconductor particles are prepared, and in the step (c), these suspensions are alternately filtered through the porous substrate to form a deposited layer with a pn junction structure.

37. A method for manufacturing a porous semiconductor according to any of claims 29 to 36, wherein an average size of the semiconductor particles is from 0.01 to 5 fÊ

m.

46. A method for manufacturing a porous semiconductor in which a porous insulating layer, a porous semiconductor layer, and a porous insulating layer are laminated on a porous substrate having continuous pores and having an electrode formed on its top or bottom surface, and another electrode is formed on the top surface, the porous semiconductor emitting ultraviolet light by electroluminescence when AC voltage is applied between the electrodes, the method comprising at least steps of:

(a) preparing a suspension of gadolinium-doped semiconductor powder and a suspension of a insulator powder;

(b) filtering the suspension of a insulator powder through the porous substrate to deposit a porous insulating layer on the porous substrate surface;

(c) filtering the suspension of the semiconductor powder through the porous substrate to deposit a porous semiconductor layer on the insulating layer; and

(d) further filtering the suspension of the insulator powder through the porous substrate to deposit a porous insulating layer on the semiconductor layer.

47. A method for manufacturing a porous semiconductor in which a porous semiconductor layer comprising semiconductor particles dispersed in an insulating layer is formed on a porous substrate having continuous pores and having an electrode formed on its top or bottom surface, and another electrode is formed on the top surface, the porous semiconductor emitting ultraviolet light by electroluminescence when AC voltage is applied between the electrodes, the method comprising at least steps of:

(a) preparing a gadolinium-doped semiconductor powder;

(b) covering the semiconductor powder with an insulating layer and preparing another suspension thereof; and

(c) filtering the suspension through the porous substrate to deposit a porous semiconductor layer on the porous substrate.