Method of forming an optical aperture of a vertical cavity surface emitting laser and vertical cavity surface emitting laser
A method of forming an optical aperture of a vertical cavity surface emitting laser includes the steps of providing a layer stack of semiconductor layers, the semiconductor layers including an intermediate layer comprising a semiconductor material suitable to be oxidized and oxidizing the intermediate layer to an oxidation width so as to form an oxidized outer region and a non-oxidized central region in the intermediate layer. The method also includes removing at least a part of the oxidized outer region so as to form a gap where the oxidized outer region or the part of the oxidized outer region has been removed, depositing an electrically non-conducting material on walls of the gap with a thickness smaller than a thickness of the gap, and filling a remaining void of the gap with a further material.
1. A method of forming an optical aperture of a vertical cavity surface emitting laser, comprising:
providing a layer stack of semiconductor layers, the semiconductor layers including an intermediate layer comprising a semiconductor material suitable to be oxidized,
oxidizing the intermediate layer to an oxidation width so as to form an oxidized outer region and a non-oxidized central region in the intermediate layer,
removing at least a part of the oxidized outer region so as to form a gap where the oxidized outer region or the part of the oxidized outer region has been removed,
depositing an electrically non-conducting material on walls of the gap with a thickness smaller than a thickness of the gap, and
filling, after the depositing of the electrically non-conducting material, a remaining void of the gap with a further material.
2. The method of claim 1 , wherein the providing of the layer stack includes:
epitaxially growing the layer stack,
etching the layer stack to form a pre-form of a mesa and a support structure at least partially surrounding the pre-form of the mesa, the support structure comprising an outer supporting region and at least one supporting web connecting the outer support region with the pre-form of the mesa, wherein the pre-form of the mesa includes the intermediate layer.
3. The method of claim 2 , wherein etching the layer stack is performed such that the pre-form of the mesa has a tapering outer wall.
4. The method of claim 3 , further comprising, after depositing the electrically non-conducting material in the gap, trim etching the pre-form of the mesa to obtain a final mesa having a straight outer wall.
5. The method of claim 1 , wherein the intermediate layer has a thickness larger than thicknesses of semiconductor layers adjacent to the intermediate layer.
6. The method of claim 5 , wherein the intermediate layer has a thickness in a range from about 80 nm to about 100 nm.
7. The method of claim 1 , wherein the semiconductor material of the intermediate layer is an Al-based semiconductor material.
8. The method of claim 1 , wherein removing at least part of the oxidized outer region of the intermediate layer is performed by etching using a hydrofluoric acid dip or a fluorine gas phase based etching process.
9. The method of claim 1 , wherein depositing the electrically non-conducting material is performed using atomic layer deposition.
10. The method of claim 1 , wherein the electrically non-conducting material is deposited on the walls of the gap with a thickness in a range from about 2 nm to about 5 nm.
11. The method of claim 1 , wherein the electrically non-conducting material is Al 2 O 3 or oxidized TiN or TiO 2 .
12. The method of claim 1 , wherein the further material is AlN or SiN.
13. The method of claim 1 , wherein the filling of the remaining void with a further material is performed using fluid chemical vapor deposition.
14. The method of claim 1 , wherein oxidizing the intermediate layer comprises wet-oxidation at a temperature in a range from about 320° C. to 350° C. and at a pressure of higher than 500 mbar.
15. A vertical cavity surface emitting laser, comprising:
a layer stack of semiconductor layers, the semiconductor layers including at least one intermediate layer comprising a semiconductor material and forming an optical aperture of the vertical cavity surface emitting laser,
wherein the at least one intermediate layer has a central region comprising the semiconductor material, and an outer region comprising a deposited layer of electrically non-conducting material deposited on walls of a gap formed by removal of oxidized material from at least a part of the outer region, wherein the deposited layer has a thickness which is smaller than a thickness of the intermediate layer, and the outer region additionally comprises a further material filling a remaining void of the gap not filled by the layer of electrically non-conductive material.