Buried heterostucture device having integrated waveguide grating fabricated by single step MOCVD
View Patent ↗The device is an optoelectronic device or transparent waveguide device that comprises a growth surface, a growth mask, an optical waveguide core mesa and a cladding layer. The growth mask is located on the semiconductor surface and defines an elongate growth window having a periodic grating profile. The optical waveguide core mesa is located in the growth window and has a trapezoidal cross-sectional shape. The cladding layer covers the optical waveguide core mesa and extends over at least part of the growth mask. Such devices are fabricated by providing a wafer comprising a growth surface, growing an optical waveguide core mesa on the growth surface by micro-selective area growth at a first growth temperature and covering the optical waveguide core mesa with cladding material at a second growth temperature, lower than the first growth temperature.
1. A device, comprising:
a growth surface;
a growth mask on the growth surface, the growth mask defining an elongate growth window having a periodic grating profile;
an optical waveguide core mesa located in the growth window and having a trapezoidal cross-sectional shape;
a first cladding layer covering the optical waveguide core mesa and extending over at least part of the growth mask; and
a second cladding layer, wherein the growth surface is a surface of the second cladding layer.
2. The device of claim 1 , in which:
the growth surface has a [100] crystalline orientation; and
the optical waveguide core mesa comprises sidewalls having a [111] crystalline orientation.
3. The device of claim 2 , in which the growth mask comprises opposed edges aligned parallel to the [011] crystalline direction of the growth surface.
4. The device of claim 1 , in which the optical waveguide core mesa is homogeneous in structure and has a greater refractive index than the cladding layer.
5. The device of claim 1 , in which:
the device is a distributed feedback (DFB) laser; and
the optical waveguide core mesa comprises a quantum well structure.
6. The device of claim 5 , in which the quantum well structure comprises quantum well layers comprising aluminum, gallium, indium and arsenic.
7. The device of claim 5 , in which the quantum well structure comprises quantum well layers comprising gallium, indium, arsenic and phosphorus.
8. The device of claim 5 , in which the optical waveguide core mesa additionally comprises a separate confinement heterostructure in which the quantum well structure is located.
9. The device of claim 5 , in which the optical waveguide core mesa comprises materials having a greater refractive index than the cladding layer and the periodic grating profile creates a refractive index difference of 0.001 to 0.020.
10. The device of claim 1 , in which the growth mask and the optical waveguide core mesa are similar in thickness.
11. A distributed feedback (DFB) laser device, comprising:
a growth surface;
a growth mask on the growth surface, the growth mask defining an elongate growth window having a periodic grating profile;
an optical waveguide core mesa located in the growth window and having a trapezoidal cross-sectional shape; and
a cladding layer covering the optical waveguide core mesa and extending over at least part of the growth mask, wherein the periodic grating profile produces a refractive index difference in the optical waveguide core mesa sufficient to provide a distributed Bragg reflection to the optical waveguide core mesa, in which the growth mask further comprises a multiple-layer structure in which one of the layers comprises the periodic grating profile.
12. The device of claim 11 , in which:
the optical waveguide core mesa comprises sidewalls having a width;
a first growth temperature is at a temperature at which adatoms have a surface diffusion length greater than the width of the sidewalls; and
a second growth temperature is at a temperature at which the adatoms have a surface diffusion length less than the width of the sidewalls.
13. The device of claim 12 , additionally comprising growing a sublayer of the cladding material on the optical waveguide core mesa by micro-selective area growth.
14. The device of claim 13 , in which growing the sublayer of the cladding material comprises setting a third growth temperature to a temperature intermediate between the first growth temperature and the second growth temperature.