Semiconductor lasers and processes for the planarization of semiconductor lasers
A laser structure may include a substrate, an active region arranged on the substrate, and a waveguide arranged on the active region. The waveguide may include a first surface and a second surface that join to form a first angle relative to the active region. A material may be deposited on the first surface and the second surface of the waveguide.
1. A laser structure, comprising:
a substrate;
an active region over the substrate;
a semiconductor layer over the active region, the semiconductor layer comprising a dovetail waveguide between a first side surface, a second side surface, a top surface, and a lower surface of the semiconductor layer, the dovetail waveguide comprising a first waveguide side surface, a second waveguide side surface, and a central top waveguide surface of the semiconductor layer, the first waveguide side surface joining the lower surface of the semiconductor layer at a first angle, and the second waveguide side surface joining the lower surface of the semiconductor layer at a second angle; and
a material between the central top waveguide surface, the first waveguide side surface, the lower surface, the first side surface, and the top surface of the semiconductor layer on one side of the dovetail waveguide, and between the central top waveguide surface, the second waveguide side surface, the lower surface, the second side surface, and the top surface of the semiconductor layer on another side of the dovetail waveguide, with an opening in the material at the central top waveguide surface of the semiconductor layer, the material planarizing the first angle and the second angle of the dovetail waveguide between the central top waveguide surface, the top surface, the lower surface, the first side surface, and the second side surface of the semiconductor layer, wherein the material comprises an insulating layer of one of MgO or MgF 2 .
2. The laser structure of claim 1 , wherein:
the first angle is less than ninety degrees; and
the second angle is less than ninety degrees.
3. The laser structure of claim 1 , wherein the material has a dielectric constant below 10 in a frequency range up to 50 GHz.
4. The laser structure of claim 1 , wherein the material comprises an insulating layer deposited on the first waveguide side surface and deposited on the second waveguide side surface to planarize the first angle and the second angle.
5. The laser structure of claim 1 , wherein the central top waveguide surface of the semiconductor layer comprises a top surface of the dovetail waveguide.
6. The laser structure of claim 5 , wherein the opening in the material exists at the top surface of the dovetail waveguide.
7. The laser structure of claim 6 , wherein:
the material comprises an insulating layer evaporated onto the first side waveguide surface, the second waveguide side surface, the lower surface of the semiconductor layer, and a portion of the central top waveguide surface of the dovetail waveguide to planarize the dovetail waveguide; and
the opening in the material comprises an opening in the insulating layer at the top surface of the dovetail waveguide.
8. The laser structure of claim 7 , further comprising:
a metal layer over the insulating layer, the metal layer being deposited at near to normal incidence on the insulating layer and on the opening at the top surface of the dovetail waveguide; and
a bond pad attached to the metal layer for electrical conductivity to the top surface of the dovetail waveguide.
9. The laser structure of claim 1 , further comprising at least one facet.
10. The laser structure of claim 9 , wherein the at least one facet is formed in the active region.
11. The laser structure of claim 1 , wherein the insulating layer consists of MgO.
12. The laser structure of claim 1 , wherein the material has a dielectric constant, in a range between 10 and 1, closer to 1 than to 10.
13. A method of fabricating a laser structure, comprising:
arranging an active region over a substrate;
arranging a semiconductor layer over the active region, the semiconductor layer comprising a dovetail waveguide between a first side surface, a second side surface, a top surface, and a lower surface of the semiconductor layer, the dovetail waveguide comprising a first waveguide side surface, a second waveguide side surface, and a central top waveguide surface of the semiconductor layer, the first waveguide side surface joining the lower surface of the semiconductor layer at a first angle, and the second waveguide side surface joining the lower surface of the semiconductor layer at a second angle; and
depositing an insulating layer between the central top waveguide surface, the first waveguide side surface, the lower surface, the first side surface, and the top surface of the semiconductor layer on one side of the dovetail waveguide, and between the central top waveguide surface, the second waveguide side surface, the lower surface, the second side surface, and the top surface of the semiconductor layer on another side of the dovetail waveguide, with an opening in the insulating layer at the central top waveguide surface of the semiconductor layer, the insulating layer planarizing the first angle and the second angle of the dovetail waveguide between the central top waveguide surface, the top surface, the lower surface, the first side surface, and the second side surface of the semiconductor layer, wherein the insulating layer comprises of one of MgO or MgF 2 .
14. The method of claim 13 , further comprising depositing a metal layer over the insulating layer at near to normal incidence on the insulating layer and on the opening at the top surface of the dovetail.
15. The method of claim 13 , wherein the insulating layer consists of MgO.
16. The method of claim 13 , wherein the insulating layer has a dielectric constant below 10 in a frequency range up to 50 GHz.
17. The method of claim 13 , wherein the insulating layer has a dielectric constant, in a range between 10 and 1, closer to 1 than to 10.
18. The method of claim 13 , wherein depositing the insulating layer comprises evaporating the insulating layer on the first waveguide side surface, on the second waveguide side surface, and on the lower surface of the semiconductor layer.
19. The method of claim 13 , wherein depositing the insulating layer comprises:
supporting the substrate at an angle with respect to an evaporant stream;
heating the substrate; and
electron beam evaporating of MgO into the evaporant stream, the evaporant stream being directed toward the first waveguide side surface, the second waveguide side surface, and the lower surface of the semiconductor layer for depositing the insulating layer on the first waveguide side surface, on the second waveguide side surface, and on the lower surface of the semiconductor layer.