High-Speed VCSEL Device

Abstract

A Vertical Cavity Surface Emitting Laser (VCSEL) includes a reflecting surface of the VCSEL. A gain region is positioned on the distributed Bragg reflector that generates optical gain. The gain region comprises a first and second multiple quantum well stack, a tunnel junction positioned between the first and second multiple quantum well stack, and a current aperture positioned on one of the first and second multiple quantum well stack. The current aperture confines a current flow in the gain region. A partially reflective surface and the reflective surface forming a VCSEL resonant cavity, wherein an output optical beam propagates from the partially reflecting surface.

We claim: 
     
         1 . A Vertical Cavity Surface Emitting Laser (VCSEL) comprising:
 a) a reflecting surface of the VCSEL;   b) a gain region positioned on the reflective surface that generates optical gain, the gain region comprising:
 i. a first and second multiple quantum well stack; 
 ii. a tunnel junction positioned between the first and second multiple quantum well stack; and 
 iii. a current aperture positioned on one of the first and second multiple quantum well stack, the current aperture confining a current flow in the gain region; and 
   c) a partially reflective surface, the reflective surface, and the partially reflective surface forming a VCSEL resonant cavity, wherein an output optical beam propagates from the partially reflecting surface.   
     
     
         2 . The VCSEL of  claim 1  wherein the reflecting surface comprises a distributed Bragg reflector. 
     
     
         3 . The VCSEL of  claim 1  wherein the partially reflecting surface comprises a distributed Bragg reflector. 
     
     
         4 . The VCSEL of  claim 1  wherein the reflecting surface comprises a sub-wavelength grating structure. 
     
     
         5 . The VCSEL of  claim 1  wherein the partially reflecting surface comprises a sub-wavelength grating structure. 
     
     
         6 . The VCSEL of  claim 1  wherein the reflecting surface comprises a combination of a distributed Bragg reflector and a sub-wavelength grating structure. 
     
     
         7 . The VCSEL of  claim 6  wherein the sub-wavelength grating structure is configured to reduce an electrical resistance of the reflecting surface. 
     
     
         8 . The VCSEL of  claim 6  wherein the sub-wavelength grating structure is configured to reduce a photon lifetime in the gain region. 
     
     
         9 . The VCSEL of  claim 6  wherein the combination of the distributed Bragg reflector and the sub-wavelength grating structure forming the reflecting surface is configured to reduce a number of distributed Bragg reflector layers required in the distributed Bragg reflector to provide a desired reflectivity, thereby reducing an RC time constant of the VCSEL. 
     
     
         10 . The VCSEL of  claim 1  wherein the partially reflecting surface comprises a combination of a distributed Bragg reflector and a sub-wavelength grating structure. 
     
     
         11 . The VCSEL of  claim 10  wherein the sub-wavelength grating structure is configured to reduce an electrical resistance of the partially reflecting surface. 
     
     
         12 . The VCSEL of  claim 10  wherein the sub-wavelength grating structure is configured to reduce a photon lifetime in the gain region. 
     
     
         13 . The VCSEL of  claim 10  wherein the combination of the distributed Bragg reflector and the sub-wavelength grating structure forming the partially reflecting surface is configured to reduce a number of distributed Bragg reflector layers required in the distributed Bragg reflector to provide a desired reflectivity, thereby reducing an RC time constant of the VCSEL. 
     
     
         14 . The VCSEL of  claim 10  further comprising a waveguide positioned proximate to the sub-wavelength grating structure that couples the output optical beam propagating from the partially reflecting surface. 
     
     
         15 . The VCSEL of  claim 14  wherein the waveguide comprises a planar waveguide. 
     
     
         16 . The VCSEL of  claim 1  further comprising a semiconductor substrate positioned such that the partially reflecting surface is positioned between the semiconductor substrate and the reflecting surface such that the output optical beam passes through the substrate. 
     
     
         17 . The VCSEL of  claim 1  further comprising a semiconductor substrate positioned such that the reflecting surface is positioned between the semiconductor substrate and the partially reflecting surface. 
     
     
         18 . The VCSEL of  claim 1  further comprising a second partially reflecting surface comprising a sub-wavelength grating positioned adjacent to the partially reflecting surface, the reflecting surface, the partially reflecting surface, and the second partially reflecting surface forming an extended-cavity VCSEL. 
     
     
         19 . The VCSEL of  claim 18  wherein the sub-wavelength grating couples into a waveguide. 
     
     
         20 . The VCSEL of  claim 1  further comprising a first electrical contact formed on a substrate and a second electrical contact formed on one of the reflecting surface or the partially reflecting surface for applying electrical current to activate the VCSEL, wherein the first and second electrical contact are accessible from a same side of the VCSEL. 
     
     
         21 . The VCSEL of  claim 20  wherein the second electrical contact is formed on the partially reflecting surface and comprises a laser aperture for transmitting the VCSEL output optical beam. 
     
     
         22 . The VCSEL of  claim 1  wherein the current aperture comprises an oxidized semiconductor layer. 
     
     
         23 . The VCSEL of  claim 1  wherein the current aperture comprises a high resistivity semiconductor layer formed by ion implantation. 
     
     
         24 . The VCSEL of  claim 1  further comprising a second current aperture positioned on the other of the first and second multiple quantum well stack, the second current aperture confining the current flow in the gain region. 
     
     
         25 . The VCSEL of  claim 1  wherein a laser cavity mode of the VCSEL resonant cavity comprises a node positioned at the tunnel junction. 
     
     
         26 . The VCSEL of  claim 1  wherein the gain region further comprises a third multiple quantum well stack and a second tunnel junction positioned between the second and the third quantum well stack. 
     
     
         27 . The VCSEL of  claim 26  wherein the gain region further comprises a fourth multiple quantum well stack and a third tunnel junction positioned between the third and fourth quantum well stack. 
     
     
         28 . A top emitting Vertical Cavity Surface Emitting Laser (VCSEL) comprising:
 a) a high reflecting distributed Bragg reflector epitaxially grown on a semiconductor substrate;   b) a gain region that generates optical gain comprising multiple semiconductor layers epitaxially grown above the high reflecting distributed Bragg reflector, the gain region comprising:
 i. a first and second multiple quantum well stack; 
 ii. a tunnel junction positioned between the first and second multiple quantum well stack; and 
 iii. a current aperture positioned on one of the first and second multiple quantum well stack, the current aperture confining a current flow in the gain region; 
   c) a partially reflecting distributed Bragg reflector epitaxially grown above the gain region to form a VCSEL resonant cavity with the high reflecting distributed Bragg reflector, wherein an output optical beam propagates from the partially reflecting distributed Bragg reflector;   d) a bottom electrical contact formed on the semiconductor substrate; and   e) a top electrical contact formed on the partially reflecting distributed Bragg reflector, the top and bottom electrical contacts configured to receive an electrical current that activates the VCSEL.   
     
     
         29 . The top emitting VCSEL of  claim 28  wherein the top electrical contact comprises a laser aperture for transmitting the optical beam from the partially reflecting distributed Bragg reflector. 
     
     
         30 . The top emitting VCSEL of  claim 28  further comprising a sub-wavelength grating structure positioned adjacent to the high reflecting distributed Bragg reflector. 
     
     
         31 . The top emitting VCSEL of  claim 30  wherein the sub-wavelength grating structure is configured to reduce an electrical resistance required for the high reflecting distributed Bragg reflector. 
     
     
         32 . The top emitting VCSEL of  claim 30  wherein the sub-wavelength grating structure is configured to reduce a photon lifetime in the gain region. 
     
     
         33 . The top emitting VCSEL of  claim 30  wherein the combination of the high reflecting distributed Bragg reflector and the sub-wavelength grating structure is configured to reduce a number of distributed Bragg reflector layers required in the high reflecting distributed Bragg reflector to provide a desired reflectivity, thereby reducing an RC time constant of the VCSEL. 
     
     
         34 . The top emitting VCSEL of  claim 28  further comprising a sub-wavelength grating structure positioned adjacent to the partially reflecting distributed Bragg reflector. 
     
     
         35 . The top emitting VCSEL of  claim 34  wherein the sub-wavelength grating structure is configured to reduce electrical resistance required for the partially reflecting distributed Bragg reflector. 
     
     
         36 . The top emitting VCSEL of  claim 34  wherein the sub-wavelength grating structure is configured to reduce photon lifetime in the gain region. 
     
     
         37 . The top emitting VCSEL of  claim 34  wherein the combination of the partially reflecting distributed Bragg reflector and the sub-wavelength grating structure is configured to reduce a number of distributed Bragg reflector layers required in the partially reflecting distributed Bragg reflector to provide a desired reflectivity, thereby reducing an RC time constant of the VCSEL. 
     
     
         38 . The top emitting VCSEL of  claim 34  further comprising a waveguide positioned proximate to the sub-wavelength grating structure that couples the output optical beam propagating from the partially reflecting distributed Bragg reflector. 
     
     
         39 . The top emitting VCSEL of  claim 38  wherein the waveguide comprises a planar waveguide. 
     
     
         40 . The top emitting VCSEL of  claim 28  wherein the current aperture comprises an oxidized semiconductor layer. 
     
     
         41 . The top emitting VCSEL of  claim 28  wherein the current aperture comprises a high resistivity semiconductor layer. 
     
     
         42 . The top emitting VCSEL of  claim 28  further comprising a second current aperture positioned on the other of the first and second multiple quantum well stack, the second current aperture confining the current flow in the gain region. 
     
     
         43 . The top emitting VCSEL of  claim 28  wherein a laser cavity mode of the VCSEL resonant cavity comprises a node positioned at the tunnel junction. 
     
     
         44 . A bottom emitting Vertical Cavity Surface Emitting Laser (VCSEL) comprising:
 a) a partially reflecting distributed Bragg reflector epitaxially grown on a semiconductor substrate;   b) a gain region that generates optical gain comprising multiple semiconductor layers epitaxially grown above the partially reflecting distributed Bragg reflector, the gain region comprising:
 i. a first and second multiple quantum well stack; 
 ii. a tunnel junction positioned between the first and second multiple quantum well stack; and 
 iii. an aperture positioned on one of the first and second multiple quantum well stack, the aperture confining a current flow in the gain region; 
   c) a high reflecting distributed Bragg reflector epitaxially grown above the gain region to form a VCSEL resonant cavity with the partially reflecting distributed Bragg reflector, wherein an output optical beam propagates from the partially reflecting distributed Bragg reflector through the semiconductor substrate;   d) a bottom electrical contact formed on the substrate; and   e) a top electrical contact formed on the high reflecting distributed Bragg reflector, the top and bottom electrical contracts configured to receive an electrical current that activates the VCSEL.   
     
     
         45 . The bottom emitting VCSEL of  claim 44  further comprising a sub-wavelength grating structure positioned adjacent to the partially reflecting distributed Bragg reflector. 
     
     
         46 . The bottom emitting VCSEL of  claim 45  wherein the sub-wavelength grating structure is configured to reduce an electrical resistance required for the partially reflecting distributed Bragg reflector. 
     
     
         47 . The bottom emitting VCSEL of  claim 45  wherein the sub-wavelength grating structure is configured to reduce a photon lifetime in the gain region. 
     
     
         48 . The bottom emitting VCSEL of  claim 45  wherein the combination of the partially reflecting distributed Bragg reflector and the sub-wavelength grating structure is configured to reduce a number of distributed Bragg reflector layers required in the partially reflecting distributed Bragg reflector to provide a desired reflectivity, thereby reducing an RC time constant of the VCSEL. 
     
     
         49 . The bottom emitting VCSEL of  claim 44  further comprising a sub-wavelength grating structure positioned adjacent to the high reflecting distributed Bragg reflector. 
     
     
         50 . The bottom emitting VCSEL of  claim 49  wherein the sub-wavelength grating structure is configured to reduce electrical resistance required for the high reflecting distributed Bragg reflector. 
     
     
         51 . The bottom emitting VCSEL of  claim 49  wherein the sub-wavelength grating structure is configured to reduce photon lifetime in the gain region. 
     
     
         52 . The bottom emitting VCSEL of  claim 49  wherein the combination of the high reflecting distributed Bragg reflector and the sub-wavelength grating structure is configured to reduce a number of distributed Bragg reflector layers required in the high reflecting distributed Bragg reflector to provide a desired reflectivity, thereby reducing an RC time constant of the VCSEL. 
     
     
         53 . The bottom emitting VCSEL of  claim 49  further comprising a waveguide positioned proximate to the sub-wavelength grating structure that couples the output optical beam propagating from the partially reflecting distributed Bragg reflector. 
     
     
         54 . The bottom emitting VCSEL of  claim 53  wherein the waveguide comprises a planar waveguide. 
     
     
         55 . The bottom emitting VCSEL of  claim 44  wherein the current aperture comprises an oxidized semiconductor layer. 
     
     
         56 . The bottom emitting VCSEL of  claim 44  wherein the current aperture comprises a high resistivity semiconductor layer. 
     
     
         57 . The bottom emitting VCSEL of  claim 44  further comprising a second current aperture positioned on the other of the first and second multiple quantum well stack, the second current aperture confining the current flow in the gain region. 
     
     
         58 . The bottom emitting VCSEL of  claim 44  wherein a laser cavity mode of the VCSEL resonant cavity comprises a node positioned at the tunnel junction. 
     
     
         59 . A method of fabricating a Vertical Cavity Surface Emitting Laser (VCSEL) comprising:
 a) epitaxially growing a first reflecting distributed Bragg reflector on a semiconductor substrate;   b) epitaxially growing a gain region comprising a first and second multiple quantum well stack, a tunnel junction positioned between the first and second multiple quantum well stack, and a current aperture positioned on one of the first and second multiple quantum well stack;   c) epitaxially growing a second reflecting distributed Bragg reflector above the gain region to form a VCSEL resonant cavity with the first reflecting distributed Bragg reflector, wherein an output optical beam propagates from one of the first and second reflecting distributed Bragg reflector;   d) forming a first electrical contact on the semiconductor substrate; and   e) forming a second electrical contact on the second partially reflecting distributed Bragg reflector, the first and second electrical contacts being configured to receive an electrical current that activates the VCSEL.   
     
     
         60 . The method of  claim 59  wherein the first reflecting distributed Bragg reflector comprises a high reflecting distributed Bragg reflector and the second distributed Bragg reflector comprises a partially reflecting distributed Bragg reflector. 
     
     
         61 . The method of  claim 60  further comprising growing a sub-wavelength grating structure adjacent to the first reflecting distributed Bragg reflector. 
     
     
         62 . The method of  claim 61  further comprising selecting the sub-wavelength grating structure so that it reduces a number of distributed Bragg reflector layers required in the first distributed Bragg reflector to provide a desired reflectivity, thereby reducing an RC time constant of the VCSEL. 
     
     
         63 . The method of  claim 60  further comprising growing a sub-wavelength grating structure adjacent to the second reflecting distributed Bragg reflector. 
     
     
         64 . The method of  claim 63  further comprising selecting the sub-wavelength grating structure so that it reduces a number of distributed Bragg reflector layers required in the second distributed Bragg reflector to provide a desired reflectivity, thereby reducing an RC time constant of the VCSEL. 
     
     
         65 . The method of  claim 64  further comprising forming a waveguide positioned proximate to the sub-wavelength grating structure that couples the output optical beam propagating from the partially reflecting surface. 
     
     
         66 . The method of  claim 64  further comprising forming a current aperture in between the first and second multiple quantum well stack.