Top-emission VCSEL-array with integrated diffuser
A radiation source includes a semiconductor substrate, an array of vertical-cavity surface-emitting lasers (VCSELs) formed on the substrate, which are configured to emit optical radiation, and a transparent crystalline layer formed over the array of VCSELs. The transparent crystalline layer has an outer surface configured to diffuse the radiation emitted by the VCSELs.
1. A radiation source, comprising:
a semiconductor substrate;
an array of vertical-cavity surface-emitting lasers (VCSELs) formed on the substrate, which are configured to emit optical radiation with a native divergence; and
a crystalline layer formed over the array of VCSELs and having an outer surface configured to diffuse the radiation emitted by the individual VCSELs so as to increase the angular divergence of the optical radiation emitted from the individual VCSELs beyond the native divergence.
2. The radiation source according to claim 1 , wherein the crystalline layer is transparent.
3. The radiation source according to claim 1 , wherein the outer surface of the crystalline layer is patterned to define microlenses having different, respective optical powers.
4. The radiation source according to claim 3 , wherein the microlenses are arrayed in an irregular pattern over the VCSELs.
5. The radiation source according to claim 1 , wherein the outer surface of the crystalline layer is randomly roughened.
6. The radiation source according to claim 1 , wherein the crystalline layer comprises an epitaxial layer of a semiconductor material.
7. The radiation source according to claim 6 , wherein the array of VCSELs comprises multiple epitaxial layers formed on the substrate, and wherein the epitaxial layer of the semiconductor material matches one of the epitaxial layers of the VCSELs.
8. The radiation source according to claim 6 , and comprising anode contacts electrically connected to the VCSELs through the crystalline layer.
9. The radiation source according to claim 1 , wherein the crystalline layer comprises a dielectric material.
10. A method of manufacturing a radiation source, the method comprising:
forming an array of vertical-cavity surface-emitting lasers (VCSELs) on a semiconductor substrate, such that the VCSELs are configured to emit optical radiation with a native divergence;
forming a crystalline layer over the VCSEL array; and
etching an outer surface of the crystalline layer to create a surface structure that diffuses optical radiation emitted by the individual VCSELs so as to increase the angular divergence of the optical radiation emitted from the individual VCSELs beyond the native divergence.
11. The method according to claim 10 , wherein etching the outer surface comprises forming microlenses having different, respective optical powers.
12. The method according to claim 11 , wherein the microlenses are arrayed in an irregular pattern over the VCSELs.
13. The method according to claim 11 , wherein forming microlenses comprises:
forming a photoresist layer over the crystalline layer;
photolithographically patterning the photoresist layer so as to define precursors for microlenses;
baking the patterned photoresist layer so as to cause the precursors to reflow into rounded shapes;
transferring the rounded shapes into the crystalline layer by etching so as to form the microlenses in the crystalline layer; and
removing the photoresist remaining on the etched crystalline layer.
14. The method according to claim 10 , wherein etching the outer surface comprises randomly roughening the outer surface by etching.
15. The method according to claim 10 , wherein the crystalline layer comprises an epitaxial layer of a semiconductor material.
16. The method according to claim 15 , and comprising forming anode contacts for the VCSELs over the crystalline layer.
17. The method according to claim 10 , wherein the crystalline layer comprises a dielectric material.
18. A radiation source, comprising:
a semiconductor substrate;
one or more vertical-cavity surface-emitting lasers (VCSELs) formed on the substrate, which are configured to emit optical radiation;
a diffusing layer formed over each VCSEL, configured to diffuse the radiation emitted by the VCSEL; and
anode electrodes of the VCSELs formed over the diffusing layer.
19. The radiation source according to claim 18 , wherein the diffusing layer comprises a crystalline material.
20. The radiation source according to claim 18 , wherein the diffusing layer comprises an amorphous material.