Nitride based semiconductor optical device, epitaxial wafer for nitride based semiconductor optical device, and method of fabricating semiconductor light-emitting device
In the nitride based semiconductor optical device LE 1 , the strained well layers 21 extend along a reference plane SR 1 tilting at a tilt angle α from the plane that is orthogonal to a reference axis extending in the direction of the c-axis. The tilt angle α is in the range of greater than 59 degrees to less than 80 degrees or greater than 150 degrees to less than 180 degrees. A gallium nitride based semiconductor layer P is adjacent to a light-emitting layer SP− with a negative piezoelectric field and has a band gap larger than that of a barrier layer. The direction of the piezoelectric field in the well layer W 3 is directed in a direction from the n-type layer to the p-type layer, and the piezoelectric field in the gallium nitride based semiconductor layer P is directed in a direction from the p-type layer to the n-type layer. Consequently, the valence band, not the conduction band, has a dip at the interface between the light-emitting layer SP− and the gallium nitride based semiconductor layer P.
1. A nitride based semiconductor optical device comprising:
a first gallium nitride based semiconductor region;
a light-emitting layer including a well layer and a barrier layer, the well layer being composed of a strained hexagonal gallium nitride based semiconductor, and the barrier layer being composed of gallium nitride based semiconductor; and
a second gallium nitride based semiconductor region,
the light-emitting layer being provided between the first gallium nitride based semiconductor region and the second gallium nitride based semiconductor region;
the first gallium nitride based semiconductor region including one or more n-type gallium nitride semiconductor layers;
the second gallium nitride based semiconductor region including a gallium nitride based semiconductor layer and one or more p-type gallium nitride semiconductor layers, the gallium nitride based semiconductor layer having a band gap larger than that of the barrier layer;
each of the well layer and the barrier layer extending along a reference plane, the reference plane tilting at a tilt angle in the range of 59 degrees to less than 80 degrees and greater than 150 degrees to less than 180 degrees from a plane orthogonal to a reference axis, the reference axis extending in the direction of a c-axis;
a piezoelectric field in the light-emitting layer including a component of a direction opposite to a direction from the second gallium nitride based semiconductor region toward the first gallium nitride based semiconductor region;
the gallium nitride based semiconductor layer of the second gallium nitride based semiconductor region being adjacent to the light-emitting layer; and
the gallium nitride based semiconductor layer of the second gallium nitride based semiconductor region including one of an electron blocking layer and a cladding layer.
2. The nitride based semiconductor optical device according to claim 1 , wherein
the well layer comprises InGaN; and
the barrier layer comprises one of GaN and InGaN.
3. The nitride based semiconductor optical device according to claim 1 , wherein the tilt angle is in the range of 62 degrees to less than 80 degrees.
4. The nitride based semiconductor optical device according to claim 1 , wherein the tilt angle is in the range of greater than 150 degrees to 170 degrees.
5. The nitride based semiconductor optical device according to claim 1 , further comprising a substrate of a hexagonal semiconductor of In S Al T Ga 1-S-T N (0≦S≦1, 0≦T≦1, 0≦S+T≦1), wherein
a primary surface of the substrate extends along a reference plane tilting from a plane orthogonal to a c-axis of the hexagonal semiconductor at a tilt angle in a range of 59 degrees to less than 80 degrees and greater than 150 degrees to less than 180 degrees; and
the first gallium nitride based semiconductor region, the light-emitting layer, and the second gallium nitride based semiconductor region are arranged in a direction of a predetermined axis on the primary surface of the substrate.
6. The nitride based semiconductor optical device according to claim 5 , wherein
the substrate includes plural first regions and plural second regions, the first regions extend in a direction of the c-axis and have a threading dislocation density larger than a first threading dislocation density, and the second regions extend in the direction of the c-axis and have a threading dislocation density smaller than the first threading dislocation density;
the first and second regions are alternately arranged; and
the first and second regions reach the primary surface of the substrate.
7. The nitride based semiconductor optical device according to claim 6 , wherein the second regions have a threading dislocation density of less than 1×10 7 cm −2 .
8. The nitride based semiconductor optical device according to claim 5 , wherein
the first gallium nitride based semiconductor region, the light-emitting layer, and the second gallium nitride based semiconductor region constitute a semiconductor laminate on the primary surface of the substrate;
the substrate has an electrical conductivity; and
the hexagonal nitride based semiconductor optical device further comprises a first electrode provided on the semiconductor laminate and a second electrode provided on a back side of the substrate.
9. The nitride based semiconductor optical device according to claim 1 , wherein
the light-emitting layer includes first and second optical guide layers and an active layer having a quantum-well structure;
the quantum-well structure includes the well layer and the barrier layer; and
the active layer is provided between the first optical guide layer and the second optical guide layer.
10. The nitride based semiconductor optical device according to claim 1 , wherein the reference plane tilts toward a direction of an a-axis.
11. The nitride based semiconductor optical device according to claim 1 , wherein the reference plane tilts toward a direction of an m-axis.
12. The nitride based semiconductor optical device according to claim 1 , wherein the gallium nitride based semiconductor layer of the second gallium nitride based semiconductor region comprises p-type Al X Ga Y In 1-X-Y N (0<X≦1, 0≦Y≦1, 0<X+Y≦1) containing at least aluminum.
13. An epitaxial wafer for a nitride based semiconductor optical device, comprising:
a first gallium nitride based semiconductor region;
a light-emitting layer including a strained well layer and a barrier layer, the well layer being composed of a hexagonal gallium nitride based semiconductor, and the barrier layer being composed of a gallium nitride based semiconductor;
a second gallium nitride based semiconductor region; and
a wafer of a hexagonal semiconductor of In S Al T Ga 1-S-T N (0≦S≦1, 0≦T≦1, 0≦S+T≦1),
the light-emitting layer being provided between the first gallium nitride based semiconductor region and the second gallium nitride based semiconductor region on the wafer;
the first gallium nitride based semiconductor region including one or more n-type gallium nitride semiconductor layers;
the second gallium nitride based semiconductor region including a gallium nitride based semiconductor layer and one or more p-type gallium nitride based semiconductor layers, the gallium nitride based semiconductor layer having a band gap larger than that of the barrier layer;
each of the well layer and the barrier layer extending along a reference plane, the reference plane tilting at a tilt angle in a range of one of 59 degrees to less than 80 degrees and greater than 150 degrees to less than 180 degrees from a plane orthogonal to a reference axis, the reference axis extending in a direction of a c-axis;
a piezoelectric field in the light-emitting layer including a component of a direction opposite to a direction from the second gallium nitride based semiconductor region toward the first gallium nitride based semiconductor region;
the gallium nitride based semiconductor layer of the second gallium nitride based semiconductor region being adjacent to the light-emitting layer;
the gallium nitride based semiconductor layer of the second gallium nitride based semiconductor region including one of an electron blocking layer and a cladding layer; and
the barrier layer comprising one of GaN and InGaN.
14. The epitaxial wafer according to claim 13 , wherein the primary surface of the wafer extends along a plane tilting from a plane orthogonal to the c-axis of the hexagonal semiconductor at a tilt angle in a range of 59 degrees to less than 80 degrees and greater than 150 degrees to 170 degrees.
15. The epitaxial wafer according to claim 13 , wherein a maximum distance between two points on an edge of the wafer is 45 millimeters or more.
16. The epitaxial wafer according to claim 13 , wherein the wafer is composed of electrically conductive GaN.
17. The epitaxial wafer according to claim 13 , wherein
the first gallium nitride based semiconductor region, the light-emitting layer, and the second gallium nitride based semiconductor region are arranged in a predetermined axial direction on the primary surface of the wafer; and
a direction of the reference axis is different from a predetermined axial direction.
18. The epitaxial wafer according to claim 13 , wherein the tilt angle is in the range of 62 degrees to less than 80 degrees.
19. The epitaxial wafer according to claim 13 , wherein the tilt angle is in the range of greater than 150 degrees to 170 degrees.