Nitride semiconductor light emitting device
A nitride semiconductor light-emitting device includes a nitride semiconductor light-emitting chip including an active layer for outputting polarized light, the active layer having a non-polar plane or a semi-polar plane as a growth plane; and a light-transmissive cover for transmitting light from the active layer. The light-transmissive cover includes a first light-transmissive member located in an area, among areas to the side of the nitride semiconductor light-emitting chip, and in a direction perpendicular to a polarization direction of the polarized light, and a second light-transmissive member located in an area above the nitride semiconductor light-emitting chip. The first light-transmissive member has a higher diffuse transmittance than the second light-transmissive member.
1. A nitride semiconductor light-emitting diode, comprising:
a nitride semiconductor light-emitting chip including an active layer for outputting polarized light, the active layer having a non-polar plane or a semi-polar plane as a growth plane;
a first light-transmissive member for transmitting light from the active layer, the first light-transmissive member being arranged at a side surface of the nitride semiconductor light-emitting chip, the side surface being located in a direction perpendicular to a polarization direction of the polarized light; and
a wavelength converting member for converting a wavelength of the polarized light which has emitted from the active layer; and
wherein:
the first light-transmissive member includes a light-transmissive substrate and a plurality of particles,
the plurality of particles have a refractive index different from that of the light-transmissive substrate,
the first light-transmissive member includes the plurality of particles at not less than 0.4% by weight and not more than 15% by weight,
the plurality of particles are formed of at least one material selected from the group consisting of TiO 2 , SiO 2 , ZrO 2 , Nb 2 O 5 , ZnO, Al 2 O 3 and AlN,
the first light-transmissive member does not include a fluorescent material,
the wavelength converting member contains a fluorescent material,
the wavelength converting layer is plate-like,
the plate-like wavelength converting layer covers the nitride semiconductor light-emitting chip,
the first-transmissive member is not interposed between the nitride semiconductor light-emitting chip and the plate-like wavelength converting layer, when viewed in a cross-sectional view of the nitride semiconductor light-emitting diode, and
the plate-like wavelength converting layer is parallel to the active layer, when viewed in a cross-sectional view of the nitride semiconductor light-emitting diode.
2. The nitride semiconductor light-emitting diode of claim 1 , wherein:
in the case where an elliptical shape which has a shorter axis in the polarization direction and a longer axis in a direction perpendicular to the polarization direction and has a centroid of the nitride semiconductor light-emitting chip as the center is defined as seen in a plan view parallel to the growth plane; and a longer radius of the longer axis is α represented by the following expression 1, a shorter radius of the shorter axis is β represented by the following expression 2, the first light-transmissive member has an absorption coefficient A[cm −1 ], and one side of the nitride semiconductor light-emitting chip has a length of L;
the plurality of particles are present in at least a part of the first light-transmissive member that is located in the elliptical shape:
α=2.3 /A+L/ 2 expression 1
β=α/2=(2.3 /A+L/ 2)/2 expression 2.
3. The nitride semiconductor light-emitting diode of claim 1 , wherein the plurality of particles have an average particle diameter of not less than 10 nm and not more than 3000 nm.
4. The nitride semiconductor light-emitting diode of claim 1 , wherein:
the nitride semiconductor light-emitting chip includes a first light extraction plane which is a top surface thereof and a second light extraction plane which is parallel to the polarization direction of the polarized light, the second light extraction plane being a side surface; and
the second light extraction plane is in contact with the first light extraction plane or faces the first light extraction plane while another member or a space is interposed therebetween.
5. The nitride semiconductor light-emitting diode of claim 4 , wherein a ratio of an area size of the second light extraction plane to an area size of the first light extraction plane is not less than 40%.
6. The nitride semiconductor light-emitting diode of claim 4 , wherein at least 50% of light going out of the second light extraction plane is incident on the first light-transmissive member.
7. The nitride semiconductor light-emitting diode of claim 4 , wherein a plurality of projection and recess portions are formed on the first light extraction plane.
8. The nitride semiconductor light-emitting diode of claim 7 , wherein the plurality of projection and recess portions are each formed of a semi-spherical recess or projection portion.
9. The nitride semiconductor light-emitting diode of claim 7 , wherein the plurality of projection and recess portions are each formed of a striped recess or projection portion as seen in a plan view parallel to the growth plane.
10. The nitride semiconductor light-emitting diode of claim 9 , wherein an angle formed between a extending direction of the striped projection and recess portions and the polarization direction of the active layer is not less than 0 degrees and less than 5 degrees.
11. The nitride semiconductor light-emitting diode of claim 9 , wherein an angle formed between a extending direction of the striped projection and recess portions and the polarization direction of the active layer is not less than 5 degrees and not more than 90 degrees.