Multi element, multi color solid state LED/laser

• US 20060255347A1
• Filed: 07/10/2006
• Published: 11/16/2006
• Est. Priority Date: 11/19/1999
• Status: Active Grant

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Keller, Bernd, DenBaars, Steven P., Tarsa, Eric J., Thibeault, Brian, Mack, Michael
• Granted Patent: US 8,035,117 B2
• Time in Patent Office: Days
• US Class Current: 257/89
• CPC Class Codes: H01L 25/0756 Stacked arrangements of devices
• CPC Class Codes: H01L 27/15 including semiconductor components having potential barriers, specially adapted for light emission
• CPC Class Codes: H01L 27/153 in a repetitive configuration, e.g. LED bars
• 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 33/08 with a plurality of light emitting regions, e.g. laterally discontinuous light emitting layer or photoluminescent region integrated within the semiconductor body H01L27/15 takes precedence
• CPC Class Codes: H01L 33/30 containing only elements of Group III and Group V of the Periodic Table
• CPC Class Codes: H01L 33/343 characterised by the doping materials
• CPC Class Codes: H01L 33/502 Wavelength conversion materials
• CPC Class Codes: H01L 33/504 Elements with two or more wavelength conversion materials
• CPC Class Codes: H01S 3/0627 the resonator being monolithic, e.g. microlaser
• CPC Class Codes: H01S 3/0941 of a laser diode
• CPC Class Codes: H01S 3/09415 the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
• CPC Class Codes: H01S 3/1623 chromium, e.g. Alexandrite
• CPC Class Codes: H01S 3/1628 characterised by a semiconducting matrix
• CPC Class Codes: H01S 5/0206 Substrates, e.g. growth, shape, material, removal or bonding; specific crystal orientation H01S5/3202
• CPC Class Codes: H01S 5/0287 Facet reflectivity
• CPC Class Codes: H01S 5/1032 Coupling to elements comprising an optical axis that is not aligned with the optical axis of the active region
• CPC Class Codes: H01S 5/183 having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
• CPC Class Codes: H01S 5/18361 Structure of the reflectors, e.g. hybrid mirrors
• CPC Class Codes: H01S 5/32341 : blue laser based on GaN or GaP

Abstract

A light emitting diode (LED) grown on a substrate doped with one or more rare earth or transition element. The dopant ions absorb some or all of the light from the LED'"'"'s active layer, pumping the electrons on the dopant ion to a higher energy state. The electrons are naturally drawn to their equilibrium state and they emit light at a wavelength that depends on the type of dopant ion. The invention is particularly applicable to nitride based LEDs emitting UV light and grown on a sapphire substrate doped with chromium. The chromium ions absorb the UV light, exciting the electrons on ions to a higher energy state. When they return to their equilibrium state they emit red light and some of the red light will emit from the LED'"'"'s surface. The LED can also have active layers that emit green and blue and UV light, such that the LED emits green, blue, red light and UV light which combines to create white light. Alternatively, it can have one active layer and grown on a sapphire substrate doped with Cr, Ti, and Co such that the substrate absorbs the UV light and emits blue, green, and red light. The invention is also capable of providing a tunable LED over a variety of color shades. The invention is also applicable to solid state laser having one or more active layers emitting UV light with the laser grown on a sapphire substrate doped with one or more rare earth or transition elements.

Claims

1. A solid state light emitting device, comprising:

a light emitting diode (LED), including;

an active layer;

a pair of oppositely doped layers on opposite sides of said active layer which cause said active layer to emit light at a predetermined wavelength in response to an electrical bias across said doped layers; and

a doped substrate, said active and doped layers disposed successively on said substrate such that said substrate absorbs at least some of said light from said active layer and re-emits light at a different wavelength, said LED emitting a combination of light from said substrate and said active layer.

2. The light emitting device of claim 1, comprising at least one said active layers and at least a pair of oppositely doped layers, said active layers between two oppositely doped layers which cause said active layers to emit light at a predetermined wavelength is response to a bias across said oppositely doped layers and said substrate absorbs at least some of said light from at least one of said active layers and re-emits light at a different wavelength.

3. The light emitting device of claim 1, further comprising electrical contacts on each said oppositely doped layer to apply said bias across said oppositely doped layers.

8. The light emitting device of claim 1, wherein said active layer emits UV light and said substrate comprises sapphire doped with chromium, said substrate absorbing some of said UV light and re-emitting red light.

10. The light emitting device of claim 1, wherein the light emitting from said device comprises the light emitting from said active layer in combination with the light emitted from said doped substrate.

11. The light emitting device of claim 2, comprising a LED, said active layers emitting blue, green and UV light and said substrate comprising sapphire doped with chromium which absorbs said UV light and re-emits red light, said LED emits blue, green, UV and red light when all said active layers are emitting, in a white light combination.

12. The light emitting device of claim 11, having three active layers emitting blue, green and UV light, wherein each said active layer can selectively emit light, said LED emitting primarily red, green, or blue light when one of said active layer is emitting, or said LED emitting primarily purple, aqua, yellow, or white light when more than one said active layer is emitting.

13. The light emitting device of claim 2, comprising a LED, said active layers emitting blue and yellow light, said substrate doped with chromium such that it absorbs at least some of said yellow light and emits red light.

18. The light emitting device of claim 1, wherein said active emits UV light, and said substrate doped by one or more rare earth or transition element in separate color centers, each said color center absorbs UV light and re-emits it as a different color.

19. The light emitting device of claim 2, comprising a LED wherein said active layers emit blue light and UV light, said substrate absorbs at least some of said UV light and re-emits red light, said LED further comprising downconverting material around the surface of said LED that absorbs some of said blue light emitting from that surface and re-emits yellow light.

20. The light emitting device of claim 1, comprising a solid state laser and further comprising mirrors on opposing surfaces, both said light from said active layer and said light absorbed and re-emitted by said doped substrate reflected between said mirrors to achieve stimulated emission.

21. The light emitting device of claim 20, wherein said active layers emit UV light and said substrate is sapphire doped with cobalt, said laser providing stimulated emission of UV and green light.

22. The light emitting device of claim 20, wherein said active layers emit UV light and said substrate is sapphire doped with chromium, said laser providing stimulated emission of UV and red light.

23. The light emitting device of claim 1, further comprising electrical circuitry integrated with said device on a common substrate.

9. A light emitting diode (LED), comprising:

an active layer;

a pair of oppositely doped layers on opposite sides of said active layer which cause said active layer to emit omnidirectional light at a predetermined wavelength in response to an electrical bias across said doped layers; and

a doped substrate, said active and doped layers disposed successively on said substrate such that said substrate absorbs at least some of said light from said active layer and re-emits omnidirectional light at a different wavelength, said LED emitting a combination of light from said substrate and said active layer, wherein said active layer emits yellow light and said substrate comprises sapphire doped with chromium, said substrate absorbing some of said yellow light and re-emitting red light.

14. A light emitting diode (LED), comprising:

an active region;

a pair of oppositely doped layers on opposite sides of said active layer which cause said active region to emit light at a predetermined wavelength in response to an electrical bias across said doped layers; and

a doped substrate, said active region and doped layers disposed successively on said substrate such that said substrate absorbs at least some of said light from said active region, said substrate doped throughout with a plurality of impurities such that said impurities simultaneously absorb the light of said active layer and each re-emits a respective color of light.

4. The LED of claim 14, wherein said active region comprises multiple quantum wells or single quantum wells.

5. The LED of claim 14, wherein said substrate comprises a material from the group consisting of sapphire, spinel, silicon carbide, gallium nitride, quartz YAGI, garnet, lithium gallate, lithium niobate, zinc oxide, and oxide single crystal.

6. The LED of claim 14, wherein said substrate is doped with a plurality of rare earth or transition elements.

7. The LED of claim 14, wherein said substrate is doped with a plurality of impurities from the group consisting of chromium, titanium, iron, erbium, neodymium, praseodymium, europium, thulium, ytterbium and cerium.

15. The light emitting device of claim 14, wherein said active layer emits UV light and said substrate is doped throughout with chromium, titanium, and cobalt, said doped substrate absorbing said UV light and emitting red, green, and blue light.

24. The LED of claim 14, wherein said doped substrate is doped using solid state diffusion, ion implantation, beam evaporation, sputtering, or laser doping.

16. A light emitting diode (LED), comprising:

an active region;

a pair of oppositely doped layers on opposite sides of said active layer which cause said active region to emit light at a predetermined wavelength in response to an electrical bias across said doped layers; and

a doped substrate, said active region and doped layers disposed successively on said substrate such that said substrate absorbs at least some of said light from said active region, said substrate doped with a plurality of impurities such that it absorbs the light of said active layer and re-emits more than one color of light, wherein said active region emits UV light, and said substrate is doped by a plurality of rare earth or transition elements in a plurality of separate color centers that each absorbs UV light and re-emits a different color of light, the emission of said active layer being controllable such that said active layer can emit primarily over a selected one or more of said color centers.

17. The light emitting device of claim 16, further comprising electrical contacts on said oppositely doped layers to selectively apply said bias to said active layer above said color centers.

52. The LED of claim 16, further comprising a means for selectively applying a bias to a portion of said active region above each of said plurality of color centers causing said active layer to emit light that is primarily absorbed by said color center below said selectively biased portion of said active layer and re-emitted as a different color.

53. The LED of claim 52, wherein said oppositely doped layers comprise an n-type and a p-type layer wherein said p-type layer is the top layer of said LED and said n-type layer is between said active region and said substrate, and wherein said means for selectively applying said bias comprises a contact to said n-type layer and a plurality of contacts to said p-type layer, each of said plurality of p-type contacts arranged over a respective one of said plurality of color centers.

25. A method for generating light from a solid state light emitting device, comprising:

providing a light emitting diode having an active layer surrounded by a pair of oppositely doped layers, all of which are disposed on a doped substrate that is doped with a plurality of impurities, each of which comprises a separate color center;

exciting an optical emission from said active layer within a first wavelength range;

selectively applying at least a portion of said optical emission to one or more of said separate impurity color centers to stimulate emission from said doped substrate within different wavelength ranges depending on said plurality of impurities color centers; and

transmitting a combination of said optical emission and substrate emission as said LED'"'"'s light.

26. The method of claim 25, wherein said doped substrate comprises sapphire, silicon carbide, gallium nitride, quartz YAGI, garnet, lithium gallate, lithium niobate, zinc oxide, or oxide single crystal.

27. The method of claim 25, wherein said substrate is doped with a plurality of rare earth or transition elements.

28. The method of claim 25, wherein said substrate is doped with a plurality of impurities from the group consisting of chromium, titanium, iron, erbium, neodymium, praseodymium, europium, thulium, ytterbium and cerium.

29. The method of claim 25, wherein said doped substrate is doped using solid state diffusion, ion implantation, beam evaporation, sputtering, or laser doping.

30. A nitride based light emitting diode (LED), comprising:

a plurality of active layers each of which is capable of emitting light at a predetermined wavelength;

a means for selectively causing each of said plurality of active layers to emit light alone or in combination with others of said plurality of active layers; and

a doped substrate, said plurality of active layers arranged vertically on said substrate with a plurality of doped semiconductor layers with each of said active layers sandwiched between two doped layers, said substrate absorbing at least some of said light from at least one of said plurality of active layers and re-emitting light at a different wavelength.

31. The LED of claim 30, that emits a combination of light from said plurality of active layers and said substrate.

32. The light emitting device of claim 30, further comprising at least two pairs of electrical contacts, each of said at least two pairs of electrical contacts arranged to apply a bias across a respective one of said pairs of oppositely doped layers.

33. The LED of claim 30, wherein each of said plurality of active layers comprises multiple quantum wells, single quantum wells or double heterostructures.

34. The LED of claim 30, wherein said substrate comprises a material from the group consisting of sapphire, spinel, silicon carbide, gallium nitride, quartz YAGI, garnet, lithium gallate, lithium niobate, zinc oxide, and oxide single crystal.

35. The LED of claim 30, wherein said substrate is doped with at least one rare earth or transition element.

36. The LED of claim 30, wherein said substrate is doped with at least one impurity from the group consisting of chromium, titanium, iron, erbium, neodymium, praseodymium, europium, thulium, ytterbium and cerium.

37. The LED of claim 30, wherein said means for causing each of said plurality of active layers to emit light being capable of causing different ones of the active layers to emit light such that the light emitting from said LED comprises the light emitting from at least one of said plurality of active layers or the light emitting from at least one of said plurality of active layers in combination with the light emitted from said doped substrate.

38. The LED of claim 30, wherein said plurality of active layers comprises three active layers emitting blue, green and UV light respectively, said substrate comprising sapphire doped with chromium which absorbs said UV light and re-emits red light, said LED emitting blue, green, UV and red light from said substrate, in a white light combination, when all said active layers are emitting.

39. The LED of claim 30, wherein said plurality of active layers comprises three active layers emitting blue, green and UV light respectively, wherein each of said active layers can selectively emit light, said LED emitting primarily red, green, or blue light when one of said active layers is emitting, or said LED emitting primarily purple, aqua, yellow, or white light when more than one of said active layers is emitting.

40. The LED of claim 30, wherein said plurality of active layers comprises two active layers emitting blue and yellow light respectively, said substrate doped with chromium such that it absorbs at least some of said yellow light and emits red light.

45. The LED of claim 30, wherein said active layers emit UV light, and said substrate is doped by one or more rare earth or transition element in separate color centers, each said color center absorbs UV light and re-emits it as a different color.

46. The LED of claim 30, wherein said plurality of active layers emit blue light and UV light, said substrate absorbing at least some of said UV light and re-emitting red light, said LED further comprising downconverting material around the surface of said LED that absorbs some of said blue light emitting from that surface and re-emits yellow light.

47. The LED of claim 30, further comprising electrical circuitry integrated with said LED on a common substrate.

54. The LED of claim 30, wherein said means for causing each of said plurality of active layers to emit light comprises an n-type layer and a plurality of p-type layers, said n-type layer disposed between the first of said vertically arranged active layers and said substrate, said p-type layers and successive active layers alternating on said first of said active layers, with a p-type layer being the top layer, said plurality of active layers separately emitting light by causing a bias to be applied across said n-type layer and one of said plurality of p-type layers.

55. The LED of claim 54, wherein said means for causing each of said plurality of active layers to emit light further comprises an n-type layer contact and a plurality of p-type layer contacts, said n-type layer contact contacting said n-type layer and each of said plurality of p-type contacts contacting a respective one of said plurality of p-type layers.

41. A light emitting diode, comprising:

an active layer;

a pair of oppositely doped layers on opposite sides of said active layer which cause said active layer to emit light at a predetermined wavelength in response to an electrical bias across said doped layers; and

a doped substrate, said active layer and doped layers arranged in a stack on said substrate, said substrate absorbing at least some of said light from said active layer and re-emitting light at a different wavelength, said substrate doped throughout with a plurality of impurities such that said substrate absorbs the light from said active layer, and re-emits more than one color of light.

42. A light emitting diode, comprising:

an active layer;

a pair of oppositely doped layers on opposite sides of said active layer which cause said active layer to emit light at a predetermined wavelength in response to an electrical bias across said doped layers; and

a doped substrate, said active layer and doped layer arranged in a stack on said substrate such that said substrate absorbs at least some of said light from said active layer and re-emits light at a different wavelength, and wherein said substrate is doped throughout with chromium, titanium, and cobalt, said doped substrate absorbing said active layer light and emitting red, green, and blue light.

43. A light emitting diode (LED), comprising:

an active layer;

a pair of oppositely doped layers on opposite sides of said active layer which cause said active layer to emit light at a predetermined wavelength in response to an electrical bias across said doped layers; and

a doped substrate, said active layer and doped layer arranged in a stack on said substrate such that said substrate absorbs at least some of said light from said active layer and re-emits light at a different wavelength, and wherein said substrate is doped by one or more rare earth or transition element in a plurality of separate color centers each of which absorbs UV light and re-emits a different color of light.

44. The LED of claim 43, further comprising a means for selectively applying a bias to a portion of said plurality of active layers above each of said plurality of color centers causing said active layer to emit light that is primarily absorbed by said color center below said selectively biased portion of said active layer and re-emitted as a different color.

48. A solid state laser, comprising:

an active layer;

a pair of oppositely doped layers on opposite sides of said active layer which cause said active layer to emit light at a predetermined wavelength in response to an electrical bias across said doped layers;

a doped substrate, said active and doped layers disposed successively on said substrate such that said substrate absorbs at least some of said light from said active layer and re-emits light at a different wavelength;

two mirrors arranged on opposing sides of the substrate, active and doped layers to cause stimulated emission of a combination of light from said substrate and said active layer as a collimated/coherent beam.

49. The laser of claim 48, wherein said active layers emits UV light and said substrate is sapphire doped with cobalt, said laser providing stimulated emission of UV and green light combined.

50. The laser of claim 48, wherein said active layers emit UV light and said substrate is sapphire doped with chromium, said laser providing stimulated emission of UV and red light combined.

51. The laser of claim 48, further comprising electrical circuitry integrated with said device on a common substrate.