VCSEL with protrusion having inclined side walls formed in p-side semiconductor layer
A vertical cavity surface emitting laser element includes a first light reflecting film, a nitride semiconductor layered body, a p-electrode and a second light reflecting film. The nitride semiconductor layered body includes an n-side semiconductor layer disposed on the first light reflecting film, an active layer disposed on the n-side semiconductor layer, and a p-side semiconductor layer disposed on the active layer. The p-side semiconductor layer includes a protrusion and a surface around the protrusion. The p-electrode is in contact with an upper surface of the protrusion, and extends to the surface around the protrusion. The p-electrode is light-transmissive. The second light reflecting film is disposed on the p-electrode. A height of the protrusion as measured from the surface around the protrusion is smaller than a thickness of the p-electrode.
1 . A vertical cavity surface emitting laser element, comprising:
a first light reflecting film;
a nitride semiconductor layered body including
an n-side semiconductor layer disposed on or above the first light reflecting film,
an active layer disposed on or above the n-side semiconductor layer, and
a p-side semiconductor layer disposed on or above the active layer, the p-side semiconductor layer including
a protrusion and
a surface around the protrusion;
a p-electrode in contact with an upper surface of the protrusion, and extending to the surface around the protrusion, the p-electrode being light-transmissive;
a second light reflecting film disposed on the p-electrode;
an insulating film spaced apart from the upper surface of the protrusion in the plan view and covering at least a portion of the surface around the protrusion of the p-side semiconductor layer, wherein
a height of the protrusion as measured from the surface around the protrusion is smaller than a thickness of the p-electrode,
a p-type impurity concentration of a layer constituting an upper surface of the protrusion is higher than a p-type impurity concentration of the surface around the protrusion,
a planar area of an upper surface of the p-electrode is larger than a planar area of the upper surface of the protrusion, and an outer edge of the upper surface of the p-electrode is located inward of an outer edge of an upper surface of the p-side semiconductor layer in a plan view,
the insulating film is spaced apart from the second light reflecting film in the plan view, and
the insulating film covers at least a part of the upper surface of the p-electrode.
2 . The vertical cavity surface emitting laser element according to claim 1 , wherein
the protrusion includes a lateral surface extending between the upper surface and the surface around the protrusion, and
an angle of inclination of the lateral surface of the protrusion with respect to the surface around the protrusion is greater than 0 degrees, and equal to or less than 60 degrees.
3 . The vertical cavity surface emitting laser element according to claim 1 , wherein
the second light reflecting film includes a dielectric layered film, and is disposed on the p-electrode over the protrusion and at least a part of the surface around the protrusion.
4 . The vertical cavity surface emitting laser element according to claim 1 , wherein
the thickness of the p-electrode is greater than or equal to 5 nm and equal to or less than 100 nm.
5 . The vertical cavity surface emitting laser element according to claim 2 , wherein
the thickness of the p-electrode is greater than or equal to 5 nm and equal to or less than 100 nm.
6 . The vertical cavity surface emitting laser element according to claim 1 , wherein
the height of the protrusion is greater than or equal to 1 nm and equal to or less than 30 nm.
7 . The vertical cavity surface emitting laser element according to claim 4 , wherein
the height of the protrusion is greater than or equal to 1 nm and equal to or less than 30 nm.
8 . The vertical cavity surface emitting laser element according to claim 2 , wherein
the height of the protrusion is greater than or equal to 1 nm and equal to or less than 30 nm.
9 . The vertical cavity surface emitting laser element according to claim 1 , further comprising
a p-pad electrode connected to the p-electrode in a region laterally spaced apart from the protrusion.
10 . The vertical cavity surface emitting laser element according to claim 5 , wherein
the p-pad electrode is spaced apart from the second light reflecting film.
11 . The vertical cavity surface emitting laser element according to claim 1 , wherein
the first light reflecting film includes a semiconductor multilayer film.
12 . The vertical cavity surface emitting laser element according to claim 1 , wherein
the p-side semiconductor layer includes a p-side cladding layer, and a p-side contact layer disposed on the p-side cladding layer,
the upper surface of the protrusion is defined by the p-side contact layer, and
the surface around the protrusion is defined by the p-side cladding layer.
13 . The vertical cavity surface emitting laser element according to claim 1 , further comprising
a heat dissipation substrate facing the second light reflecting film.
14 . The vertical cavity surface emitting laser element according to claim 1 , wherein
an arithmetic average roughness of the upper surface of the protrusion is in a range of 0.1 nm to 2 nm, and
an arithmetic average roughness of the surface around the protrusion is in a range of 0.1 nm to 2 nm.
15 . The vertical cavity surface emitting laser element according to claim 1 , wherein
a difference between the thickness of the p-electrode and the height of the protrusion is greater than or equal to 10 nm and equal to or less than 100 nm.
16 . The vertical cavity surface emitting laser element according to claim 1 , wherein
the thickness of the p-electrode is greater than or equal to 1.25 times and equal to or less than 20 times the height of the protrusion.
17 . The vertical cavity surface emitting laser element according to claim 1 , wherein
the p-type impurity concentration of the upper surface of the protrusion is in a range of 5×10 19 cm −3 to 5×10 21 cm −3 , and
the p-type impurity concentration of the surface around the protrusion is in a range of 1×10 17 cm −3 to 1×10 19 cm −3 .