Light emitting device

• US 6,878,969 B2
• Filed: 05/29/2003
• Issued: 04/12/2005
• Est. Priority Date: 07/29/2002
• Status: Expired due to Term

• Current Assignee: Panasonic Electric Works Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Asahi Matsushita Electric Works Ltd. (Panasonic Holdings Corporation)
• Inventors: Matsushima, Tomoaki, Terauchi, Ryoichi, Tanaka, Kenichiro, Kubo, Masao
• Primary Examiner(s): Wojciechowicz, Edward
• Application Number:
  US10/447,232
• Publication Number:
  US 20040016936A1
• Time in Patent Office: 684 Days
• Field of Search: 257/59, 257/79, 257/82, 257/98, 257/434, 257/435, 257/680
• US Class Current: 257/79
• CPC Class Codes: H01L 2933/0083 Periodic patterns for optical field-shaping in or on the semiconductor body or semiconductor body package, e.g. photonic bandgap structures
• CPC Class Codes: H01L 33/025 Physical imperfections, e.g. particular concentration or distribution of impurities
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers

Abstract

A semiconductor light emitting device gives a large radiation surface with an enhanced light radiating capability. A N-type GaN layer and a P-type GaN layer are stacked to define therebetween an interface where a light is generated upon application of voltage across the interface. A light guide on which the GaN layers are developed is utilized to give a wide radiation surface from which the light is given off. The radiation surface is formed with a refractor layer composed of an array of a first medium and a second medium which have individual refraction indexes different from each other and are arranged alternately across the radiation surface. Thus, the light guide can be best utilized to give a large radiation surface, yet formed with the refractor layer which reduces multiple reflections inside of the light guide for effectively passing or radiating the light transmitted through the light guide.

Claims

1. A light emitting device comprising:

a semiconductor light emitting unit producing a light, said light emitting unit being composed of a first semiconductor layer of a first conductive type and a second semiconductor layer of a second conductive type opposite to said first conductive type, said second semiconductor layer being integrally stacked on said first semiconductor layer to define therebetween an interface;

a pair of electrodes being attached respectively to said first and second semiconductor layers to apply a voltage across said interface for emitting the light from around said interface,

a light guide superimposed on said first semiconductor layer and directing the light therethrough, said first semiconductor layer being developed directly on said light guide to form a unitary structure with said light guide and said second semiconductor layer;

said light guide having a radiation surface through which said light is given off,

wherein

said radiation surface is formed with a refractor layer which comprises an array of a first medium and a second medium, said first and second mediums having refraction indexes different from each other and being arranged alternately across said radiation surface.

2. The light emitting device as set forth in claim 1, wherein

said light guide is made of a transparent crystalline substrate on which said first semiconductor layer is crystallized, and said second semiconductor layer being crystallized on said first semiconductor layer.

3. The light emitting device as set forth in claim 2, wherein

said transparent crystalline substrate is made of a material selected from a group consisting of sapphire, silicon carbide, gallium nitride, gallium arsenide, and gallium phosphide, and

each of said first and second semiconductor layers being made of a material selected from a group consisting of gallium nitride, gallium arsenide, gallium phosphide, and aluminum nitride.

4. The light emitting device as set forth in claim 2, wherein

each of said first and second mediums is spaced at a regular interval which is from ¼

to 4 times the wavelength of said light.

5. The light emitting device as set forth in claim 2, wherein

said refractor layer has an overall refraction index which is between that of a portion of said light guide other than said refractor layer and that of an environmental medium outside of said refractor layer.

6. The light emitting device as set forth in claim 2, wherein

said first medium is the medium of said transparent crystalline substrate, and

said second medium is a modified medium obtained by modifying said crystalline substrate with a laser beam irradiated on said crystalline substrate.

7. The light emitting device as set forth in claim 6, wherein

said laser beam has a pulse width less than 1 (one) pico-second.

8. The light emitting device as set forth in claim 2, wherein

said refractor layer includes an array of concavities to define said first medium as the medium of said transparent crystalline substrate between the adjacent concavities and define said second medium as an environmental medium entrapped in said concavities.

9. The light emitting device as set forth in claim 8, wherein

said concavities are formed through the steps of:

irradiating a laser beam to said radiation surface to modify the selected portions thereof into modified mediums; and

removing said modified medium to leave thereat said concavities.

10. The light emitting device as set forth in claim 9, wherein

said laser beam has a pulse width less than 1 (one) pico-second that causes no heat damage to a portion adjacent to the resulting refractory layer.

11. The light emitting device as set forth in claim 9, wherein

said modified medium is formed by an action of interference between a plurality of laser beams irradiated simultaneously from different directions.

12. The light emitting device as set forth in claim 2, wherein

said refractor layer has an array of concavities formed in said radiation surface to define said first medium by portions between the adjacent concavities and define said second medium as an environmental medium entrapped within said concavities,

said concavities having a varying width which varies from portions to portion across said radiation surface to realize the Fresnel lens.

13. The light emitting device as set forth in claim 2, wherein

said transparent crystalline substrate includes a photonic crystal structure for reflecting the light from said interface towards said radiation surface.

14. The light emitting device as set forth in claim 13, wherein

said photonic crystal structure comprises an array of pillar elements extending in a depth direction of said transparent crystalline substrate and being arranged n a regular pattern in which said pillar elements are spaced from each other by a distance corresponding to a wavelength or less of the light from said semiconductor light emitting unit.

15. The light emitting device as set forth in claim 1, wherein

said semiconductor light emitting unit includes an internal reflector area having a photonic crystal structure for directing the light from said interface towards said light guide.

16. The light emitting device a set forth in claim 2, wherein

a photonic crystal structure is formed to extend across said transparent crystalline substrate and said semiconductor unit for reflecting the light from said interface towards said radiation surface.

17. The light emitting device as set forth in claim 2, wherein

said radiation surface comprises a plurality of planar faces each forming an angle less than a critical angle with respect to a light axis of said light proceeding from a center at said interface.

18. The light emitting device as set forth in claim 2, wherein

said radiation surface is semi-spherical to shape said transparent crystalline substrate into a plan-convex lens, said plan-convex lens having its optical center coincident with a center of said interface.

19. The light emitting device as set forth in claim 1, wherein

said light guide is composed of a transparent crystalline substrate on which said first semiconductor layer is developed, and a transparent overcoat superimposed on said transparent crystalline substrate, said overcoat being made of a material different from said transparent crystalline substrate and having said radiation surface with said refractor layer.

20. The light emitting device as set forth in claim 19, wherein

said transparent crystalline substrate is made of a material selected from a group consisting of sapphire, silicon carbide, gallium nitride, gallium arsenide, and gallium phosphide, and

said overcoat being made of a material selected from a group consisting of a quartz glass, epoxy resin, silicon resin, and gallium nitride.

21. The light emitting device as set forth in claim 19, wherein

said overcoat has at its portion other than said top refractor layer a refraction index greater than that of said transparent crystalline substrate.

22. The light emitting device as set forth in claim 19, wherein

said overcoat has at its portion other than said refractory layer a refraction index smaller than that of said transparent crystalline substrate.

23. The light emitting device as set forth in claim 19, wherein

an additional refractor layer is formed at an interface between said overcoat and said crystalline substrate, said additional refractor layer comprising an array of a first medium and a second medium which have different refraction indexes and which are arrange alternately across said interface between the overcoat and the crystalline substrate.

24. The light emitting device as set forth in claim 2, wherein

an additional light guide is superimposed on said second semiconductor layer, said additional light having an additional radiation surface through which said light is given off, said additional radiation surface being formed with an additional refractor layer comprising an array of a first medium and a second medium, said first and second mediums having refraction indexes different from each other and being arranged alternately across said additional radiation surface.

25. The light emitting device as set forth in claim 1, wherein

an additional refractor layer is formed at an interface between the light guide and said first semiconductor layer, said additional refractor layer having an overall refraction index which is between those of the first semiconductor layer and said light guide.