Optical semiconductor device having uneven semiconductor layer with non-uniform carrier density
In an optical semiconductor device including a first semiconductor layer of a first conductivity type, an active layer provided on the first semiconductor layer, a second semiconductor layer of a second conductivity type provided on the active layer, an insulating layer provided on a part of the second semiconductor layer, an uneven semiconductor layer of the second conductivity type provided on another part of the second semiconductor layer, and an electrode layer provided on the insulating layer and the uneven semiconductor layer, a density of carriers of the second conductivity type being larger at a tip portion of the uneven semiconductor layer than at a bottom portion of the uneven semiconductor layer.
1. An optical semiconductor device comprising:
a first semiconductor layer of a first conductivity type;
an active layer provided on said first semiconductor layer;
a second semiconductor layer of a second conductivity type provided on said active layer;
an insulating layer provided on apart of said second semiconductor layer;
an uneven semiconductor layer of said second conductivity type provided on another part of said second semiconductor layer; and
an electrode layer provided on said insulating layer and said uneven semiconductor layer,
a density of carriers of said second conductivity type being larger at a tip portion of said uneven semiconductor layer than at a bottom portion of said uneven semiconductor layer.
2. The optical semiconductor device as set forth in claim 1 , wherein the density of said carriers at the tip portion of said uneven semiconductor layer is about four times or more the density of said carriers at the bottom portion of said uneven semiconductor layer.
3. The optical semiconductor device as set forth in claim 1 , wherein the density of said carriers is increased stepwise from the bottom portion of said uneven semiconductor layer to the tip portion thereof.
4. The optical semiconductor device as set forth in claim 1 , wherein the density of said carriers is increased continuously from the bottom portion of said uneven semiconductor layer to the tip portion thereof.
5. The optical semiconductor device as set forth in claim 1 , wherein said uneven semiconductor layer is trapezoidal-sectional.
6. The optical semiconductor device as set forth in claim 1 , wherein said uneven semiconductor layer is triangular-sectional.
7. The optical semiconductor device as set forth in claim 1 , wherein said first semiconductor layer, said active layer, said second semiconductor layer and said uneven semiconductor layer comprises III-V group nitride represented by Al x In y Ga z N where 0≦x≦1, 0≦y≦1, 0≦z≦1 and x+y+z=1.
8. The optical semiconductor device as set forth in claim 1 , wherein an index of refraction of said insulating layer is smaller than those of said first semiconductor layer, active layer and said second semiconductor layer.
9. The optical semiconductor device as set forth in claim 1 , wherein said insulating layer comprises a plurality of portions, and said uneven semiconductor layer surrounds the portions of said insulating layer.
10. The optical semiconductor device as set forth in claim 9 , wherein the portions of said insulating layer are circular.
11. The optical semiconductor device as set forth in claim 9 , wherein the portions of said insulating layer are polygonal.
12. The optical semiconductor device as set forth in claim 9 , wherein the portions of said insulating layer are arranged in a triangular lattice manner.
13. The optical semiconductor device as set forth in claim 12 , wherein said uneven semiconductor layer has a thickness “h” represented by
0.36 d≦h≦ 1.15 i
1.0μm≦ d≦ 4.0μm
1.5μm≦ i≦ 3.0μm
where “d” is a diameter or diagonal length of the portions of said insulating layer; and
“i” is an interval between the portions of said insulating layer.