Grating coupled vertical cavity optoelectronic devices

Abstract

A edge emitting waveguide laser is obtained that derives its optical power from a vertical cavity laser structure. The vertical cavity laser with top and bottom Distributed Bragg Reflectors produces stimulated emission by resonance in the vertical direction but the optical power so generated is diffracted by a second order grating into an optical mode propagating in the optical waveguide formed by the upper and lower mirrors as cladding layers. The efficiency of the diffraction grating and the reflectivity of the mirrors are maximized so that essentially all of the light is coupled into the guide and the loss through the mirrors can be neglected. The same structure can be utilized as a detector, a modulator or an amplifier. The designated laser structure to achieve this form of operation is the inversion channel laser which is a laterally injected laser having both contacts on the top side of the device. Then the anode and cathode of the laser are essentially coplanar electrodes and the device is implemented in the form of a traveling wave laser, detector, modulator or amplifier which forms the basis for very high frequency performance.

1. A resonant vertical cavity optoelectronic semiconductor device, comprising:
 an epitaxially grown distributed bragg reflector bottom mirror;  
 a first layer of N+ type GaAs deposited on said epitaxial mirror;  
 a layer of N+ type aluminum gallim arsenide disposed on said layer of GaAs;  
 a layer of P type aluminum gallim arsenide disposed on said layer of N+ type aluminum gallim arsenide;  
 a PHEMT (Pseudomorphic High Electron Mobility Transistor) epitaxial layer structure without a schottky contact and using N+ type modulating doping, disposed on said layer of P type aluminum gallium arsenide said PHEMT comprising a layer of aluminum gallium arsenide (˜15% Al), a layer of GaAs, one to three quantum wells of strained InGaAs separated by GaAs barriers, a spacer layer of aluminum gallium arsenide (˜15% Al), an N+ modulation doped layer of aluminum gallium arsenide (˜15% Al) and a gate spacer layer of aluminum gallium arsenide (˜15% Al);  
 a very thin (˜80 Å) layer of P+ type heavily doped aluminum gallium arsenide (˜15% Al) as a planar doped layer and then a cladding layer of aluminum gallium arsenide (40%-70%) of modest P type doping (˜10 17  cm −3 ) disposed on said planar doped layer;  
 an ohmic contact layer of P++ type doping deposited on said cladding layer;  
 a first layer of a top dielectric mirror deposited on said contact layer to a thickness of approximately ¼ wavelength of a specific designed frequency and etched to a controlled thickness to form an optical grating with a second order pitch for diffraction through approximately 90°, the angle of the teeth of said diffraction grating being chosen to optimize the diffraction in a specific desired output direction and to minimize the diffraction in the opposite direction and the depth of the teeth being chosen to maximize the diffraction efficiency;  
 additional layer of said top dielectric mirror deposited on said first layer of said top dielectric mirror to form a complete structure of said Distributed Bragg Reflector (DBR) mirror with very high reflectivity for a vertically resonant wave such that the diffracted energy of the grating is substantially greater than the energy transmitted through the mirror.  
 
     
     
       2. The device as defined in  claim 1 , fabricated in the form of a waveguide device with DBR mirrors performing the function of waveguide cladding regions wherein the optical energy in the guide is diffracted into a vertical cavity or is obtained by diffraction from the vertical cavity, utilizing two refractory metal emitter gate electrodes positioned on either side of said waveguide device the positive species current from said refractory emitter gate electrodes being steered into or out of the core of said device waveguide by N type implants positioned beneath said electrodes to reduce optical mode interaction with said electrodes, and utilizing ion implants self-aligned to said emitter gate electrodes to form source or drain electrodes which make electrical contact with a quantum well channel region thereby providing a source or a drain for negative species current flow, with each emitter gate and self-aligned source or drain electrode forming a coplanar transmission line. 
     
     
       3. The device as defined in  claim 2  wherein the structure of said device between said epitaxially grown bottom DBR mirror and said deposited by DBR mirror is a conventional pn semiconductor laser with either a separate confined heterostructure (SCH) or a graded index confinement scheme. 
     
     
       4. The device as defined in  claim 2 , wherein said emitter gate electrodes are biased positively with respect to said source electrodes such that stimulated emission establishes a vertically resonant optical mode which is diffracted substantially into one direction to obtain an edge emitting laser. 
     
     
       5. The device as claimed in  claim 2 , wherein a high speed electrical signal is introduced onto the transmission line to obtain a high speed traveling optical pulse in said optical waveguide such that a travelling wave laser is obtained. 
     
     
       6. The device as defined in  claim 2 , wherein said waveguide in said optoelectronic device is coupled to another passive waveguide within a monolithic integrated circuit, the core of said passive waveguide being identical to the core of said waveguide within said optoelectronic device except for the p+ contact layer and shifted in energy gap with respect to said active core by disordering techniques such that the passive waveguide has low optical loss but the interface between said active waveguide and said passive waveguide has a small index change and therefore low insertion loss. 
     
     
       7. The device as defined in  claim 2 , wherein the source electrodes are biased positively with respect to the emitter gate electrodes such that separation of photoelectrons and photoholes produced in the quantum well(s) by resonant cavity absorption is achieved and a traveling electrical wave is produced on the transmission line resulting in a high speed traveling wave detector. 
     
     
       8. The device as defined in  claim 2 , wherein it is biased as a laser above threshold, the optical output of said laser being delivered to a passive waveguide which is split into several outputs, said outputs becoming the respective optical inputs to a second set of lasers, each laser in said second set of lasers being biassed biased below its threshold level such that it amplifies its optical input and the outputs from all said amplifiers entering into passive waveguides, said passive waveguides being combined into one single waveguide, and said single waveguide delivering its power to the edge of the semiconductor chip to obtain a spatially coherent optical output with single mode power of high intensity and high brightness due to the small waveguide cross-section. 
     
     
       9. A resonant vertical cavity optoelectronic semiconductor device, comprising
 an epitaxially grown bottom mirror;    an epitaxially grown semiconductor laser layer structure located atop said bottom mirror; and    a top dielectric mirror located atop said laser layer structure, said top dielectric mirror including an optical grating and at least one mirror layer atop said grating, and said optical grating defining a plurality of openings having a pitch for diffracting light generated in said laser layer structure through approximately  90 ° such that the light exits said laser layer structure substantially parallel to said bottom mirror and said top dielectric mirror.   
     
     
       10. A device according to  claim 9 , wherein:
 said grating includes a plurality of angled teeth.   
     
     
       11. A device according to  claim 10 , wherein:
 said plurality of angled teeth are angled at about  35 °.   
     
     
       12. A device according to  claim 9 , wherein:
 said laser layer structure is disposed on said bottom mirror and said top dielectric mirror is disposed on said laser layer structure.   
     
     
       13. A device according to  claim 9 , wherein:
 said grating has a thickness of approximately {fraction ( 1 / 4 )} wavelength of a frequency of the light generated by said laser layer structure.   
     
     
       14. A device according to  claim 9 , wherein:
 said at least one mirror layer of said top dielectric mirror constituting a first distributed bragg reflector mirror, and said bottom mirror constituting a second distributed bragg mirror.   
     
     
       15. A device according to  claim 14 , wherein:
 said first and second distributed bragg mirrors have a very high reflectivity.   
     
     
       16. A device according to  claim 9 , wherein:
 said laser layer structure comprises an inversion channel laser.   
     
     
       17. A device according to  claim 16 , wherein:
 said inversion channel laser includes a first AlGaAs layer of a first semiconductor type, at least one quantum well having a layer of not intentionally doped GaAs and a layer of InGaAs, a second AlGaAs layer of a second semiconductor type, and a third AlGaAs layer of said first semiconductor type.   
     
     
       18. A device according to  claim 17 , wherein:
 said second AlGaAs layer is a modulation doped layer, and said third AlGaAs layer is separated from said modulation doped layer by a not intentionally doped fourth AlGaAs capacitance layer.   
     
     
       19. A device according to  claim 17  fabricated in the form of a waveguide device with said bottom and top mirrors performing the function of waveguide cladding regions and said laser layer structure forming a vertical cavity, said device further including waveguide implants of said second semiconductor type positioned within said laser layer structure and defining a waveguide width, two refractory metal gate electrodes positioned outside said waveguide width, and ion implants self-aligned to said gate electrodes to form source electrodes which make electrical contact with said at least one quantum well, with each gate and self-aligned source electrode forming a substantially coplanar transmission line. 
     
     
       20. A device according to  claim 19  wherein:
 said gate electrodes are biased positively with respect to said source electrodes.   
     
     
       21. A device according to  claim 19  wherein:
 a high speed electrical signal is introduced onto said transmission line to obtain a high speed traveling optical pulse in said waveguide device.   
     
     
       22. A device according to  claim 19 , wherein:
 said source electrodes are biased positively with respect to said gate electrodes such that light introduced into said vertical cavity produces a traveling electrical wave on said transmission line.   
     
     
       23. A device according to  claim 16 , wherein:
 said inversion channel laser includes, 
 a first layer of GaAs of a first semiconductor type deposited on said bottom mirror,  
 a first layer of AlGaAs of said first semiconductor type deposited on said first layer of GaAs,  
 a first layer of not intentionally doped (NID) AlGaAs atop said layer of AlGaAs,  
 at least one quantum well atop said NID AlGaAs, each quantum well having a layer of NID GaAs and a layer of InGaAs,  
 a second layer of NID AlGaAs deposited on said at least one quantum well,  
 a layer of AlGaAs of a second semiconductor type deposited on said second layer of NID AlGaAs,  
 a third layer of NID AlGaAS deposited on said layer of AlGaAs of said second semiconductor type,  
 a second layer of AlGaAs of said first semiconductor type deposited on said third layer of NID AlGaAs, and  
 a second layer of GaAs of said first semiconductor type atop said second layer of AlGaAs of said first semiconductor type atop said second layer of AlGaAs of said first semiconductor type. 
   
     
     
       24. A device according to  claim 23 , wherein:
 said first semiconductor type is p-type and said second semiconductor type is n-type.   
     
     
       25. A device according to  claim 24 , wherein:
 said first and second layers of GaAs are doped p+.   
     
     
       26. A device according to  claim 25 , wherein:
 said first and second layers of AlGaAs of said first semiconductor type each comprise a first sublayer of doped p+ AlGaAs and a second sublayer of p AlGaAs.   
     
     
       27. A device according to  claim 26 , wherein:
 said second sublayer of p AlGaAs has of said first layer of AlGaAs has a first aluminum content and a first gallium content, and said first layer of not intentionally doped (NID) AlGaAs has a second aluminum content smaller than said first aluminum content and a second gallium content larger than said first gallium content.   
     
     
       28. A device according to  claim 26 , wherein:
 said first and second layers NID AlGaAs have a first aluminum content and a first gallium content, and said layer of AlGaAs of said first semiconductor type and said layer of AlGaAs of said second semiconductor type each have a second aluminum content larger than said first aluminum content and a second gallium content smaller than said first gallium content.   
     
     
       29. A device according to  claim 25 , fabricated in the form of an active waveguide device with said bottom and top mirrors performing the function of waveguide cladding regions and said laser layer structure forming a vertical cavity, said device further including waveguide implants of said second semiconductor type positioned within said laser layer structure and defining a waveguide width, two refractory metal gate electrodes positioned outside said waveguide width, and ion implants self-aligned to said gate electrodes to form source electrodes which make electrical contact with said at least one quantum well, with each gate and self-aligned source electrode forming a substantially coplanar transmission line, said device further comprising a passive waveguide within a monolithic integrated circuit, said passive waveguide having a core identical to the core of said active waveguide device except said core of said passive waveguide not having a second p+ doped GaAs layer, and said core of said passive second waveguide being shifted in energy gap with respect to said core of said active waveguide device such that said passive waveguide has low optical loss but the interface between said active waveguide and said passive waveguide has a small index change and therefore low insertion loss. 
     
     
       30. A device according to  claim 9 , wherein:
 said laser layer structure comprises a pn laser.   
     
     
       31. A device according to  claim 30 , wherein:
 said pn laser includes a layer of a first semiconductor type of at least one of GaAs and AlGaAs, at least one quantum well having a layer of not intentionally doped GaAs and a layer of InGaAs, and a layer of a second semiconductor type of at least one of GaAs and AlGaAs.   
     
     
       32. A device according to  claim 31 , wherein:
 said layer of a first semiconductor type of at least one of GaAs and AlGaAs includes a first layer of GaAs of said first semiconductor type deposited on said bottom mirror and a first layer of AlGaAs of said first semiconductor type deposited on said first layer of GaAs.   
     
     
       33. A device according to  claim 30 , wherein:
 said pn laser includes 
 a layer of GaAs of a first semiconductor type deposited on said bottom mirror,  
 a layer of AlGaAs of said first semiconductor type deposited on said first layer of GaAs,  
 a first layer of not intentionally doped (NIDL) AlGaAs atop said layer of AlGaAs of said first semiconductor type,  
 at least one quantum well atop said NID AlGaAs, each quantum well having a layer of NID GaAs and a layer of InGaAs,  
 a second layer of NID AlGaAs deposited on said at least one quantum well,  
 a layer of AlGaAs of a second semiconductor type deposited on said second layer of NID AlGaAs,  
 a layer of GaAs of said second semiconductor type atop said layer of AlGaAs of said second semiconductor type. 
   
     
     
       34. A device according to  claim 33 , wherein:
 said first semiconductor type is n-type and said second semiconductor type is p-type.   
     
     
       35. A device according to  claim 34 , wherein:
 said layer of GaAs of said first semiconductor type is doped N+, and said layer of GaAs of said second semiconductor type is doped P+.   
     
     
       36. A resonant vertical cavity optoelectronic semiconductor device, comprising:
 an epitaxially grown bottom mirror;    a top dielectric mirror substantially parallel to said bottom mirror; and    an epitaxially grown semiconductor laser layer structure located between said bottom mirror and said top mirror, said laser layer structure generating light in a first direction substantially perpendicular to said bottom mirror and said top dielectric mirror and directing said light out of said laser layer structure in a second direction substantially parallel to said bottom mirror and said top dielectric mirror.   
     
     
       37. A resonant vertical cavity optoelectronic semiconductor device, comprising:
 an epitaxially grown bottom mirror;    top dielectric mirror substantially parallel to said bottom mirror; and    an epitaxially grown semiconductor laser layer structure located between said bottom mirror and said top mirror, said device fabricated in the form of a waveguide device with said bottom and top mirrors performing the function of waveguide cladding regions and said laser layer structure forming a vertical cavity, said device further including gate electrodes and source electrodes together forming a transmission line, wherein light traveling in said laser layer structure and a corresponding electrical signal traveling on said transmission line have substantially matched velocities.   
     
     
       38. A device according to  claim 37 , wherein:
 said electrical signal causes said laser layer structure to generate said light traveling in said laser layer structure.   
     
     
       39. A device according to  claim 37 , wherein:
 said light traveling in said laser layer structure generates said electrical signal.   
     
     
       40. A device according to  claim 37 , wherein:
 said laser layer structure includes at least one quantum well, and    said gate electrodes are positioned on either side of said waveguide device, implants of a first semiconductor type are positioned beneath said electrodes, and ion implants are self-aligned to said gate electrodes to form said source electrodes which make electrical contact with said at least one quantum well, with each gate and self-aligned source electrode forming said transmission line which is substantially coplanar.