VCSEL with self-aligned microlens to improve beam divergence

A method of making a microlens for a vertical cavity surface emitting laser (VCSEL) device, the method comprising:

• forming a reflector stack comprising a plurality of first reflector layers alternatingly stacked with a plurality of second reflector layers, wherein the plurality of first reflector layers comprise a first composition and the plurality of second reflector layers comprise a second composition different from the first composition;
• forming a microlens stack comprising a plurality of lens layers alternatively stacked with a plurality of additional reflector layers;
• performing a first etch process according to a masking layer to remove outermost edges of the microlens stack;
• performing an oxidation process to oxidize peripheral portions of the plurality of lens layers after the first etch process, wherein the oxidized peripheral portions increase in width as a distance over the reflector stack increases;
• forming one or more upper sidewall spacers along sidewalls of the masking layer and the microlens stack;
• performing a second etch process to etch the reflector stack after performing the oxidation process, the second etch process etching the reflector stack with the masking layer and the one or more upper sidewall spacers in place;
• forming one or more lower sidewall spacers along sidewalls of the reflector stack after the second etch process;
• forming a molding layer on outermost sidewalls of the one or more lower sidewall spacers, wherein the one or more lower sidewall spacers have an exposed part that protrudes outward from a top surface of the molding layer;
• removing the exposed part, but not all, of the one or more lower sidewall spacers after the second etch process is completed and removing a part, but not all, of the one or more upper sidewall spacers after the second etch process is completed;
• removing the molding layer after removing the exposed part of the one or more lower sidewall spacers;
• and
• forming top electrode contacts onto a top of the reflector stack and laterally between an outermost sidewall of the reflector stack and the one or more upper sidewall spacers after removing the part of the one or more upper sidewall spacers.

A method of making a microlens for a vertical cavity surface emitting laser (VCSEL) device, the method comprising:

• forming a reflector stack comprising a plurality of first reflector layers alternately stacked with a plurality of second reflector layers;
• forming a microlens stack comprising a plurality of lens layers alternately stacked with a plurality of additional reflector layers, wherein the plurality of lens layers have variable concentrations of a first element, and wherein concentrations of the first element at a top surface and a bottom surface of closest neighboring ones of the plurality of lens layers are approximately equal;
• performing a first etch process according to a masking layer to remove outermost edges of the microlens stack;
• performing an oxidation process to oxidize peripheral portions of the plurality of lens layers after the first etch process, wherein the oxidized peripheral portions increase in width as a distance over the reflector stack increases;
• forming one or more upper sidewall spacers along opposing sides of the microlens stack after performing the oxidation process;
• performing a second etch process to etch the reflector stack;
• forming one or more lower sidewall spacers continuously extending from a conductive layer below the reflector stack, to along a side of the reflector stack, and to along a sidewall of the one or more upper sidewall spacers;
• and
• removing a part of the one or more lower sidewall spacers and a part of the one or more upper sidewall spacers after forming the one or more lower sidewall spacers.