Light emitting device having a pseudo-continuous spectrum and lighting apparatus using the same

• US 7,026,651 B2
• Filed: 07/30/2003
• Issued: 04/11/2006
• Est. Priority Date: 07/31/2002
• Status: Expired due to Fees

• Current Assignee: Shin-Etsu Handotai Co., Ltd. (Shin-Etsu Chemical Company Limited)
• Original Assignee: Shin-Etsu Handotai Co., Ltd. (Shin-Etsu Chemical Company Limited)
• Inventors: Yamada, Masato, Takahashi, Masanobu
• Primary Examiner(s): Wilczewski, Mary
• Assistant Examiner(s): Lewis, Monica
• Application Number:
  US10/629,737
• Publication Number:
  US 20040026683A1
• Time in Patent Office: 986 Days
• Field of Search: 257 79-103
• US Class Current: 257/79
• CPC Class Codes: F21K 9/232 specially adapted for generating an essentially omnidirectional light distribution, e.g. with a glass bulb
• CPC Class Codes: F21S 10/04 simulating flames
• CPC Class Codes: F21S 6/001 being candle-shaped with varying lighting effect of simulating flames F21S10/04; string of light sources F21S4/00
• CPC Class Codes: F21S 8/04 intended only for mounting on a ceiling or the like overhead structures F21S8/02 takes precedence; details of ceiling bases F21V21/03
• CPC Class Codes: F21W 2121/00 Use or application of lighting devices or systems for decorative purposes, not provided for in codes F21W2102/00 – F21W2107/00
• CPC Class Codes: F21W 2131/109 of gardens
• CPC Class Codes: F21Y 2115/10 Light-emitting diodes [LED]
• CPC Class Codes: H01L 2224/32245 the item being metallic
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 25/0753 the devices being arranged next to each other
• 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 2924/00012 Relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/09701 Low temperature co-fired ceramic [LTCC]
• CPC Class Codes: H01L 2933/0091 Scattering means in or on the semiconductor body or semiconductor body package H01L33/22 takes precedence
• CPC Class Codes: H01L 33/06 within the light emitting region, e.g. quantum confinement structure or tunnel barrier
• 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 33/483 Containers
• CPC Class Codes: H01L 33/62 : Arrangements for conducting electric current to or from the semiconductor body, e.g. lead-frames, wire-bonds or solder balls

Abstract

A light emitting device capable of readily produce a pseudo-continuous spectrum covering a wide wavelength regions at low costs, and of totally solving various problems which have resided in the conventional light sources, and a lighting apparatus using this device is provided. The light emitting device 10 is configured so that an active layer in a double hetero light emitting layer portion composed of compound semiconductors comprises a plurality of emission unit layers differing from each other in band gap energy, and so as to emit a simulatively synthesized light having a pseudo-continuous spectrum ensuring an emission intensity of 5% or more of a peak intensity over a wavelength region of 50 nm or more.

Claims

1. A light emitting device causing emission output of a light having a pseudo-continuous spectrum which is modeled upon is a continuous spectrum obtained from a heat-radiation light source obtained by synthesizing a plurality of emissions differing in peak wavelength so as to ensure an effective wavelength region showing an emission intensity of 5% or more of a reference intensity over a wavelength region of 50 nm or more, the reference intensity being defined as an emission intensity at a peak wavelength in the synthesized spectrum,

having a double hetero light emitting layer portion composed of compound semiconductors, the double hetero light emitting layer portion having an active layer comprising a plurality of emission unit layers differing from each other in band gap energy, and the emission output of the light having a pseudo-continuous spectrum is ascribable to a combination of light emission from the individual emission unit layers,

wherein the emission unit layers comprise well layers each of which is sandwiched by two barrier layers, and

wherein well-depth of well layers in the emission unit layer is a shallower depth in a well having a shorter emission wavelength.

2. The light emitting device as claimed in claim 1, wherein emission intensity of the emission unit layer is adjusted based on thickness and/or the number of the well layers.

3. The light emitting device as claimed in claim 2, wherein the well layers, which contribute to a wavelength region where a larger emission intensity is attained in the pseudo-continuous spectrum, are disposed in a larger thickness and/or the number of layers.

4. The light emitting device as claimed in claim 1, wherein the well emission unit layer has a quantum well structure.

5. The light emitting device as claimed in claim 4, wherein the emission intensity of the emission unit layer having the quantum well structure is adjusted by the number of layers of the well layers.

6. The light emitting device as claimed in claim 4, wherein the well layers have a smaller thickness in the emission unit layer causative of a shorter emission wavelength.

7. The light emitting device as claimed in claim 1, wherein a plurality of repetitive units consisting of a set of emission unit layers having different emission wavelengths are periodically formed in the thickness-wise direction of the active layer.

8. The light emitting device as claimed in claim 7, wherein the double hetero light emitting layer portion is designed so that the main surface thereof on one side of the stacking direction serves as a light extraction surface, and so that the emission unit layer causative of a longer emission wavelength in each of the repetitive unit is disposed more further from the light extraction surface in the thickness-wise direction of the active layer.

9. The light emitting device as claimed in claim 1, wherein the plurality of emission unit layers are aligned according to an order of magnitude of the band gap energy such as ensuring a difference of 0.2 eV or less between every adjacent band gap energies.

10. The light emitting device as claimed in claim 9, wherein the effective wavelength region of the pseudo-continuous spectrum is synthesized by four or more emission unit layers differing in emission wavelength from each other.

11. The light emitting device as claimed in claim 10, wherein the pseudo-continuous spectrum has a ripple ratio of 0.1 or less over the entire portion of the effective wavelength region.

12. The light emitting device as claimed in claim 1, wherein the double hetero light emitting layer portion is composed of (Al_xGa₁₋

x)_yIn<sub>1−

y</sub>P (where, 0≦

x≦

1 and 0≦

y≦

1), and the effective wavelength region is ensured within a wavelength region from 550 nm to 670 nm, both ends inclusive.

13. The light emitting device as claimed in claim 1 having a first device and a second device as combined therein, both devices respectively having a double hetero light emitting layer portion composed of compound semiconductors, the first device having an emission wavelength of an emission unit layer contained in an active layer in the double hetero light emitting layer portion of 520 nm to 700 nm, both ends inclusive, and the second device of which having the same of 350 nm to 560 nm, both ends inclusive, and at least either of the first device and second device includes a plurality of the emission unit layers in the active layer.

14. The light emitting device as claimed in claim 13, wherein the double hetero light emitting layer of the first device is composed of (Al_xGa₁₋

x)_yIn<sub>1−

y</sub>P (where, 0≦

x≦

1 and 0≦

y≦

1), and the double hetero light emitting layer of the second device is composed of In_aGa_bAl<sub>1−

a−

b</sub>N (where, 0≦

a≦

1, 0≦

b≦

1 and a+b≦

1).

15. The light emitting device as claimed in claim 1, wherein the pseudo-continuous spectrum contains no ultraviolet emission components having a wavelength of 350 nm or shorter.

16. The light emitting device as claimed in claim 7, wherein the double hetero light emitting layer portion is designed so that the main surface thereof on one side of the stacking direction serves as a light extraction surface, and so that the emission unit layer in the repetitive unit causative of longer emission wavelength is disposed more further from the light extraction surface in the thickness-wise direction of the active layer.