Oxide aperture shaping in vertical cavity surface-emitting laser
A corrected mesa structure for a VCSEL device is particularly configured to compensate for variations in the shape of the created oxide aperture that result from anisotropic oxidation. In particular, a corrected mesa shape is derived by determining the shape of an as-created aperture formed by oxidizing a circular mesa structure, and then ascertaining the compensation required to convert the as-created shape into a desired (“target”) shaped aperture opening. The compensation value is then used to modify the shape of the mesa itself such that a following anisotropic oxidation yields a target-shaped oxide aperture.
1. A vertical cavity surface emitting laser (VCSEL) comprising:
a substrate having a top major surface;
a first distributed Bragg reflector (DBR) formed on the top major surface of the substrate, the first distributed Bragg reflector comprising a stack of layers of alternating refractive index value;
a second DBR disposed over the first DBR and comprising a stack of layers of alternating refractive index, the second DBR exhibiting an elliptical mesa structure of a predetermined cross-section geometry required to create an oxide aperture of a circular shape; and
an active layer disposed between the first DBR and the second DBR, wherein a layer within the second DBR has an larger concentration of a quickly oxidizing material than the remaining layers of the second DBR and is defined as an aperture layer that exhibits anisotropic oxidation, the aperture layer including an outer insulating boundary region coincident with sidewalls of the elliptical mesa structure and an inner oxide aperture of a circular shape, the circular shape defined by anisotropic oxidation of the aperture layer.
2. The VCSEL as defined in claim 1 wherein the VCSEL is a GaAs-based VCSEL device.
3. The VCSEL as defined in claim 2 wherein the aperture layer comprises Al x (Ga 1-x )As, with an aluminum content x greater than aluminum content of the remaining Al x (Ga 1-x )As layers of alternating refractive index value in the corrected mesa structure.
4. The VCSEL as defined in claim 3 where the aluminum content x of the aperture layer is at least about 0.90.