Radiation emitter

Abstract

An exemplary embodiment of the invention relates to a method of fabricating a radiation emitter (100) comprising the steps of fabricating a layer stack (10) that comprises a first reflector (12), an active region (13), an oxidizable layer (21-24), and a second reflector (14); and locally removing the layer stack (10), and thereby forming a mesa (M) of the radiation emitter (100), wherein said mesa (M) comprises the first reflector (12), the active region (13), the oxidizable layer (21-24) and the second reflector (14), wherein before or after locally removing the layer stack (10) and forming said mesa (M) the following steps are carried out: vertically etching blind holes (30) inside the layer stack (10), wherein the blind holes (30) vertically extend at least to the oxidizable layer (21-24) and expose the oxidizable layer (21-24); and oxidizing the oxidizable layer (21-24) via the sidewalls (31) of the blind holes (30) in lateral direction, wherein from each hole an oxidation front (32) radially moves outwards and wherein the etching is terminated before the entire oxidizable layer (21-24) is oxidized, thereby forming at least two unoxidized apertures, (40) each of which is limited by at least three oxidation fronts (32), inside the mesa.

1 . Method of fabricating a radiation emitter ( 100 ) comprising the steps of
 fabricating a layer stack ( 10 ) that comprises a first reflector ( 12 ), an active region ( 13 ), an oxidizable layer ( 21 - 24 ), and a second reflector ( 14 ); and   locally removing the layer stack ( 10 ), and thereby forming a mesa (M) of the radiation emitter ( 100 ), wherein said mesa (M) comprises the first reflector ( 12 ), the active region ( 13 ), the oxidizable layer ( 21 - 24 ) and the second reflector ( 14 ),   
       wherein 
       before or after locally removing the layer stack ( 10 ) and forming said mesa (M) the following steps are carried out:
 vertically etching blind holes ( 30 ) inside the layer stack ( 10 ), wherein the blind holes ( 30 ) vertically extend at least to the oxidizable layer ( 21 - 24 ) and expose the oxidizable layer ( 21 - 24 ); and 
 oxidizing the oxidizable layer ( 21 - 24 ) via the sidewalls ( 31 ) of the blind holes ( 30 ) in lateral direction, wherein from each hole an oxidation front ( 32 ) radially moves outwards and wherein the etching is terminated before the entire oxidizable layer ( 21 - 24 ) is oxidized, thereby forming at least two unoxidized apertures, ( 40 ) each of which is limited by at least three oxidation fronts ( 32 ), inside the mesa. 
 
     
     
         2 . Method of  claim 1  wherein
 said mesa is provided with at least two individual VCSEL units by fabricating said at least two apertures within said mesa and within the same oxidizable layer ( 21 - 24 ). 
 
     
     
         3 . Method of  claim 1  wherein
 the at least two apertures form VCSEL sub-cells that operate in parallel. 
 
     
     
         4 . Method of  claim 1  wherein
 the apertures ( 40 ) are so narrowly spaced in said mesa (M) that the resulting radiation emitter provides single mode emission. 
 
     
     
         5 . Method of  claim 1  wherein
 at least six blind holes ( 30 ) are vertically etched inside the layer stack ( 10 ), wherein the blind holes ( 30 ) vertically extend at least to the oxidizable layer ( 21 - 24 ) and expose the oxidizable layer ( 21 - 24 ); and 
 by oxidizing the oxidizable layer ( 21 - 24 ) via the sidewalls ( 31 ) of the at least six blind holes ( 30 ) in lateral direction the at least two apertures are fabricated. 
 
     
     
         6 . Method of  claim 1  wherein
 at least four apertures are fabricated within said mesa. 
 
     
     
         7 . Method of  claim 1  wherein
 at least nine blind holes ( 30 ) are vertically etched inside the layer stack ( 10 ), wherein the blind holes ( 30 ) vertically extend at least to the oxidizable layer ( 21 - 24 ) and expose the oxidizable layer ( 21 - 24 ); and 
 by oxidizing the oxidizable layer ( 21 - 24 ) via the sidewalls ( 31 ) of the blind holes ( 30 ) in lateral direction said at least four apertures are fabricated. 
 
     
     
         8 . Method of  claim 1  wherein
 a top contact layer ( 15 ) is fabricated on top of the second reflector ( 14 ), and 
 the top contact layer ( 15 ) is provided with a first conducting material ( 61 ) such that the conducting material ( 61 ) partly covers the surface of the top contact layer ( 15 ) and sections ( 15   a ) of the top contact layer ( 15 ) above the apertures ( 40 ) are left uncovered in order to allow optical radiation (P) to exit the mesa (M) without additional attenuation. 
 
     
     
         9 . Method according to  claim 1  wherein
 at least four blind holes ( 30 ) are etched inside the layer stack ( 10 ) and 
 at least one unoxidized aperture ( 40 ) is formed that is limited by at least four oxidation fronts ( 32 ). 
 
     
     
         10 . Method according to  claim 1  wherein
 a plurality of blind holes ( 30 ) is etched inside the layer stack ( 10 ), 
 wherein the blind holes ( 30 ) are arranged in a lattice-like way forming a grid having a first grid spacing (d 1 ) in a first direction (D 1 ) and a second grid spacing (d 2 ) in a second different direction (D 2 ). 
 
     
     
         11 . Method according to  claim 1  wherein
 the oxidation is carried out using processing parameters causing circular oxidation fronts ( 32 ) or 
 the oxidation is carried out using processing parameters causing anisotropic oxidation fronts ( 32 ). 
 
     
     
         12 . Radiation emitter ( 100 ) comprising
 a layer stack ( 10 ) having a first reflector ( 12 ), an active region ( 13 ), at least two apertures ( 40 ) formed by unoxidized material ( 20 ) of an oxidizable layer ( 21 - 24 ) that is partly oxidized and partly unoxidized, and a second reflector ( 14 );   wherein a mesa (M) of the emitter ( 100 ) includes at least the first reflector ( 12 ), the active region ( 13 ), the oxidizable layer ( 21 - 24 ) and the at least two apertures ( 40 ), and the second reflector ( 14 ),   wherein the mesa (M) further comprises at least three blind holes ( 30 ) which vertically extend to oxidized sections of the oxidizable layer ( 21 - 24 ), and   wherein the at least two apertures ( 40 ) are each limited by oxidation fronts ( 32 ) of at least three of said oxidized sections, and   wherein each of the blind holes ( 30 ) forms a center point of one of the oxidation fronts ( 32 ).   
     
     
         13 . Radiation emitter ( 100 ) of  claim 12   wherein the at least two apertures form VCSEL sub-cells that operate in parallel.   
     
     
         14 . Radiation emitter ( 100 ) of  claim 12   wherein the apertures ( 40 ) are so narrowly spaced in said mesa (M) that the resulting radiation emitter provides single mode emission.   
     
     
         15 . Radiation emitter ( 100 ) of  claim 12  wherein at least five blind holes ( 30 ) are located inside said mesa. 
     
     
         16 . Radiation emitter ( 100 ) of  claim 12  wherein at least four apertures are located within said mesa. 
     
     
         17 . Radiation emitter ( 100 ) of  claim 12 ,
 wherein a top contact layer ( 15 ) is located on top of the second reflector ( 14 ),   wherein a first conducting material ( 61 ) is located on top of the contact layer ( 15 ),   wherein the conducting material ( 61 ) partly covers the surface of the second contact layer ( 15 ) and   wherein sections ( 15   a ) of the second contact layer ( 15 ) above the apertures ( 40 ) are uncovered in order to allow optical radiation (P) to exit the mesa (M) without additional attenuation.   
     
     
         18 . Radiation emitter ( 100 ) of  claim 17  wherein
 the blind holes ( 30 ) are filled with the conducting material ( 61 ) or at least the sidewalls ( 31 ) of the holes ( 30 ) are covered with the conducting material ( 61 ). 
 
     
     
         19 . Radiation emitter ( 100 ) of  claim 18   wherein the conducting material forms an electrical bypass with respect to at least one of the apertures ( 40 ), and   wherein each bypassed aperture ( 40 ) is subjected to optical radiation (P), only, because electrical current bypasses the bypassed aperture ( 40 ) via the corresponding bypass.   
     
     
         20 . Radiation emitter ( 100 ) of  claim 19   wherein two or more apertures ( 40 ) are located inside the second reflector ( 14 ) and/or between the active region ( 13 ) and the second reflector ( 14 );   wherein at least the aperture ( 40 ) that is the most adjacent to the active region ( 13 ), is subjected to electrical current flow as well as optical radiation (P) when the radiation emitter ( 100 ) operates, and   wherein at least one of the remaining apertures ( 40 ) is bypassed.