INDEX AND GAIN COUPLED DISTRIBUTED FEEDBACK LASER
A method of forming a laser involves forming, on a substrate, a first epitaxial part of the laser that includes at least an active region layer surrounded by first and second waveguide layers. A dielectric layer is formed over the first epitaxial part. Two or more mask openings are patterned within the dielectric layer. The mask openings extend normal to a light-propagation direction of the laser and are spaced apart in the light-propagation direction of the laser. A second epitaxial part of the laser is formed in the mask openings using selective area epitaxy. The second epitaxial part includes a refractive grating with three-dimensional grating features.
1 . A method of forming a laser, comprising:
forming, on a substrate, a first epitaxial part of the laser comprising at least an active region layer surrounded by first and second waveguide layers;
forming a dielectric layer over the first epitaxial part;
patterning two or more mask openings within the dielectric layer, the mask openings extending normal to a light-propagation direction of the laser and are spaced apart in the light-propagation direction of the laser; and
forming, in the mask openings using selective area epitaxy, a second epitaxial part of the laser comprising a refractive grating comprising three-dimensional nano-stripes.
2 . The method of claim 1 , wherein the three-dimensional nano-stripes comprise trapezoidal cross-sections.
3 . The method of claim 1 , wherein the three-dimensional nano-stripes comprise rectangular cross-sections.
4 . The method of claim 1 , wherein the three-dimensional nano-stripes comprise triangular cross-sections.
5 . The method of claim 1 , wherein the mask openings align with a center of the nano-stripes.
6 . The method of claim 1 , wherein the active layer region, first and second waveguide layers, and three-dimensional refractive grating are formed of III-V semiconductors.
7 . The method of claim 6 , wherein the III-V semiconductors are selected from a group consisting of AlGaInN, AlGaInAs, AlGaInP, and AlGaInSb.
8 . The method of claim 1 , wherein the dielectric layer is formed of SiO 2 .
9 . The method of claim 1 , further comprising forming an electron blocking layer between one of the first and second waveguide layers and the dielectric layer.
10 . The method of claim 1 , further comprising forming a conductive cover layer over the nano-stripes, the cover having a different refractive index than the refractive grating and filling in gaps between the nano-stripes.
11 . The method of claim 10 , wherein the conductive cover layer has a lower refractive index than that of the refractive grating.
12 . The method of claim 10 , wherein the conductive cover layer is in contact with the dielectric layer.
13 . The method of claim 10 , wherein the conductive cover layer is formed of ITO.
14 . The method of claim 1 , wherein the nano-stripes extend beyond the edges of the mask openings in the light propagation direction.
15 . The method of claim 1 , wherein the nano-stripes comprise surfaces facing away from the active region that are atomically smooth.
16 . The method of claim 1 , wherein using selective area epitaxy comprises using metalorganic vapor-phase epitaxy.
17 . The method of claim 1 , wherein using selective area epitaxy comprises using molecular beam epitaxy.
18 . The method of claim 1 , wherein the use of selective area epitaxy forms the nano-stripes without etching or milling, resulting in atomically smooth surfaces on the nano-stripes.
19 . A method of forming a laser heterostructure, comprising:
performing a first epitaxial run in which a first part of the laser heterostructure is grown in an unpatterned manner, the first part comprising an active region layer surrounded by first and second waveguide layers;
interrupting the first epitaxial run to deposit a dielectric mask over an upper layer of the first part, the mask comprising openings extending normal to a light-propagation direction of the laser heterostructure and are spaced apart in the light-propagation direction of the laser heterostructure; and
performing a second epitaxial run in which selective area epitaxy is used to form a second part of the laser heterostructure, the second part comprising three-dimensional nano-stripes formed in the openings.
20 . The method of claim 19 , wherein the first and second parts of the laser heterostructure are formed of III-V semiconductors.