Quantum cascade laser structure

Abstract

A quantum cascade laser structure in accordance with the invention comprises a number of cascades ( 100 ), each of which comprises a number of alternately arranged quantum wells ( 110 a to 110 j ) and barrier layers ( 105 to 105 j ). The material of at least one quantum well ( 110 a to 110 j ) as well as the material of at least one barrier layer ( 105 to 105 j ) is under mechanical strain, with the respective strain being either a tensile strain or a compression strain. The quantum wells ( 110 a to 110 j ) and barrier layers ( 105 to 105 j ) are engineered in the quantum cascade laser structure in accordance with the invention so that existing strains are largely compensated within a cascade ( 100 ). In the quantum cascade laser structure in accordance with the invention, each material of the quantum wells ( 110 a to 110 j ) has only one constituent material and the material of at least one barrier layer ( 105 d, 105 e, 105 f ) has at least two constituent materials ( 111 a, 111 b, 112 a, 112 b, 113 a, 113 b ).

1 . Quantum cascade laser structure having a number of cascades ( 100 ) each of which comprises a number of alternately arranged quantum wells ( 110   a  to  110   j ) and barrier layers ( 105  to  105   j ), where 
 the material of at least one quantum well ( 110   a  to  100   j ) is under mechanical strain,    the material of at least one barrier layer ( 105  to  105   j ) is under mechanical strain:    the quantum wells ( 110   a  to  100   j ) and the barrier layers ( 105  to  105   j ) are coordinated such that the existing mechanical strains are largely compensated within one cascade ( 100 ),    the material of the quantum wells ( 110   a  to  110   j ) has only one constituent material each, and    the material of at least one of the barrier layers ( 105   d ,  105   e ,  105   f ) comprises at least two constituent materials ( 111   a ,  111   b ,  112   a ,  112   b ,  113   a ,  113   b ).    
     
     
         2 . Quantum cascade laser structure in accordance with  claim 1 , where each of the constituent materials comprise a number of constituents and the composition of the constituent materials of the quantum wells ( 110   a  to  110   j ) and the barrier layers ( 105  to  105   j ) from the constituents and/or the thicknesses of the quantum wells ( 110   a  to  110   j ) and the barrier layers ( 105  to  105   j ) are coordinated such that existing mechanical strain is largely compensated within one cascade ( 100 ).  
     
     
         3 . Quantum cascade laser structure in accordance with  claim 2 , where the relative ratio of the constituents of the constituent materials and/or the thickness of at least one of the quantum wells ( 110   a  to  110   j ) is selected such and/or is such that the existing strain in at least one of the barrier layers ( 105  to  105   j ) is compensated by a mechanical strain in essentially the same quantity as the mechanical strain of at least one barrier layer ( 105  to  105   j ), but with the opposite sign.  
     
     
         4 . Quantum cascade laser structure in accordance with  claim 1 , where the cascade ( 100 ) comprises an injection zone, a extraction zone and an active zone arranged between the injection zone and the extraction zone, with each zone comprising at least one barrier layer ( 105  to  105   j ) and at least one of the barrier layers ( 105   d  to  105   h ) in the active zone and/or in the injection zone having at least two constituent materials ( 111   a ,  111   b ,  112   a ,  112   b ,  113   a ,  113   b ).  
     
     
         5 . Quantum cascade laser structure in accordance with  claim 4 , where the barrier layer ( 105   f ) of the active zone which borders the injection zone has at least two constituent materials ( 113   a ,  113   b ).  
     
     
         6 . Quantum cascade laser structure in accordance with  claim 1 , where the material of at least one of the barrier layers ( 105  to  105   j ) has only one constituent material.  
     
     
         7 . Quantum cascade laser structure in accordance with  claim 6 , with the constituent material of the at least one barrier layer having only one constituent material ( 105   a  to  105   c  and  105   g  to  105   j ) is selected so as to maximize the conduction band discontinuity in the cascade ( 100 ).  
     
     
         8 . Quantum cascade laser structure in accordance with  claim 6 , where the thicknesses and the constituents of the constituent materials of the quantum wells ( 110   a  to  100   j ) and the barrier layers ( 105   a  to  105   j ) as well as the composition of the material of at least one barrier layer ( 105   d ,  105   e ,  105   f ) with at least two constituent materials ( 111   a ,  111   b ,  112   a ,  112   b ,  113   a ,  113   b ) are selected so that the wave length spectrum of the emitted laser radiation is 2.9 to 5.3 μm.  
     
     
         9 . Quantum cascade laser structure in accordance with  claim 6 , with 
 In x GA 1−x As with 0.6≦x≦1 as constituent material of the quantum wells ( 110   a  to  110   j );    In y Al 1−y As with 0.4≦y≦0.6 and In z Al 1−z As with 0≦z≦0.4 as constituent materials of at least one barrier layer ( 105   d ,  105   e ,  105   f ) with at least two constituent materials ( 111   a ,  111   b ,  112   a ,  112   b ,  113   a ,  113   b ), and    In s Al 1−s As with 0≦s≦0.4 as constituent material of the remaining barrier layers ( 105   a  to  105   c  and  105   g  to  105   j ).    
     
     
         10 . Quantum cascade laser structure in accordance with  claim 9 , with 
 In 0.73 Ga 0.27 As as constituent material of the quantum wells ( 110   a  to  110   j ),    In 0.55 Al 0.45 As and AlAs as constituent materials of at least one barrier layer ( 105   d ,  105   e ,  105   f ) with at least two constituent materials ( 111   a ,  111   b ,  112   a ,  112   b ,  113   a ,  113   b ) and    AlAs as constituent material of the remaining barrier layers ( 105   a  to  105   c  and  105   g  to  105   j ).    
     
     
         11 . Quantum cascade laser structure in accordance with  claim 1 , characterized in that the thicknesses of the quantum wells ( 110   a  to  110   j ) and/or the thicknesses of the barrier layers ( 105  to  105   j ) and/or the composition of at least one barrier layer with at least two constituent materials is selected and/or is such in particular in the active zone that the laser-active transition occurs from a number of energetically closely adjacent higher conditions (II) to an energetically lower condition ( 1 ) or a number of energetically lower and energetically closely adjacent conditions (I)  
     
     
         12 . Quantum cascade laser structure in accordance with  claim 11 , where the barrier layer ( 105   f ) of the active zone which borders on the injection zone has a thickness of 5 nm or less.  
     
     
         13 . Quantum cascade laser structure in accordance with  claim 1 , where a cascade comprises the following layers with the stated constituent materials and layer thicknesses in the stated order: 
 an In z Al 1−z As-layer with 0≦z≦0.4, in particular an AlAs layer with a thickness of 0.6 to 0.8 nm, in particular 0.75 nm;    an In x Ga 1−x As-layer with 0.6≦x≦1, in particular an In 0,73 Ga 0,27 As layer with a thickness of 3.2 to 3.6 nm, in particular 3.4 nm;    an In z Al 1−z As layer with 0≦x≦0.4, in particular an AlAs layer with a thickness of 1.2 to 1.4 nm, in particular 1.3 nm;    an In x Ga 1−x As-layer wit 0.6≦x≦1, in particular an In 0.73 Ga 0.27 As-layer with a thickness of 2.8 to 3.2 nm, in particular 3.0 nm, and an n-doping;    an In z Al 1−z As-layer with 0≦z≦0.4, in particular an AlAs-layer with a thickness of 0.8 to 1.0 nm, in particular 0.9 nm;    an In x Ga 1−x As-layer with 0.6≦x≦1, in particular an In 0.73 Ga 0.27 As-layer with a thickness of 2.4 to 2.8 nm, in particular 2.6 nm, and an n-doping;    an In z Al 1−z As-layer with 0≦z≦0.4, in particular an AlAs-layer with a thickness of 0.8 to 1.0 nm, in particular 0.9 nm;    an In x Ga 1−x As-layer with 0.6≦x≦1, in particular an In 0.73 Ga 0.27 As-layer, with a thickness of 2.1 to 2.3 nm, in particular 2.2 nm, and an n-doping;    an In y Al 1−y As-layer with 0.4≦y≦0.6, in particular an In 0.55 Al 0.45 As-layer, with a thickness of 1.3 to 1.5 nm, in particular 1.4 nm, and an n-doping;    an In z Al 1−z As-layer with 0≦z≦0.4, in particular an AlAs-layer, with a thickness of 0.8 to 1.0 nm, in particular 0.9 nm;    an In x Ga 1−x As-layer with 0.6≦x≦1, in particular an In 0.73 Ga 0.27 As-layer, with a thickness of 1.9 to 2.1 nm, in particular 2.0 nm;    an In y Al 1−y As-layer with 0.4≦y≦0.6, in particular an In 0.55 Al 0.457 As-layer, with a thickness of 1.3 to 1.5 nm, in particular 1.4 nm;    an In z Al 1−z As-layer with 0≦z≦0.4, in particular an AlAs-layer, with a thickness of 0.8 to 1.0 nm, in particular 0.9 nm;    an In x Ga 1−x As-layer with 0.6≦x≦1, in particular an In 0.73 Ga 0.27 As-layer, with a thickness of 1.7 to 1.9 nm, in particular 1.8 nm;    an In y Al 1−y As-layer with 0.4≦y≦0.6, in particular an In 0.55 Al 0.45 As-layer, with a thickness of 2.8 to 3.2 nm, in particular 3.0 nm;    an In z Al 1−z As-layer with 0≦z≦0.4, in particular an AlAs-layer, with a thickness of 0.8 to 1.0 nm, in particular 0.9 nm;    an In x Ga 1−x As-layer with 0.6≦x≦1, in particular an In 0.73 Ga 0.27 As-layer, with a thickness of 1.7 to 1.9 nm, in particular 1.8 nm;    an In z Al 1−z As-layer with 0≦z≦0.4, in particular an AlAs-layer, with a thickness of 0.8 to 1.0 nm, in particular 0.9 nm;    an In x Ga 1−x As-layer with 0.6≦x≦1, in particular an In 0.73 Ga 0.27 As-layer, with a thickness of 4.7 to 5.3 nm, in particular 5.0 nm;    an In z Al 1−z As-layer with 0≦z≦0.4, in particular an AlAs-layer, with a thickness of 1.6 to 1.8 nm, in particular 1.7 nm;    an In x Ga 1−x As-layer with 0.6≦x≦1, in particular an In 0.73 Ga 0.27 As-layer, with a thickness of 4.0 to 4.4 nm, in particular 4.2 nm;    an In z Al 1−z As-layer with 0≦z≦0.4, in particular an AlAs-layer, with a thickness of 2.0 to 2.2 nm, in particular 2.1 nm;    an In x Ga 1−x As-layer with 0.6≦x≦1, in particular an In 0.73 Ga 0.27 As-layer, with a thickness of 3.6 to 4.0 nm, in particular 3.8 nm;    an In z Al 1−z As-layer with 0≦z≦0.4, in particular an AlAs-layer, with a thickness of 0.6 to 0.8 nm, in particular 0.75 nm.    
     
     
         14 . Quantum cascade laser structure in accordance with  claim 6 , with InAlAsSb or AlAsSb as a first constituent material ( 111   a ,  112   a ,  113   a ) of at least one barrier layer ( 105   d ,  105   e ,  105   f ) having at least two constituent materials and/or with InAlAsSb in another composition than in the first constituent material as a second constituent material ( 111   b ,  112   b ,  113   b ) of at least one barrier layer ( 105   d ,  105   e ,  105   f ) with at least two constituent materials and/or with InAlAsSb or AlAsSb as constituent material of the remaining barrier layers ( 105   a  to  105   c  and  105   g  to  105   j ).  
     
     
         15 . Quantum cascade laser with a lower waveguide layer ( 30 ), an upper waveguide layer ( 40 ) and a quantum cascade laser structure ( 100 ) according to one of the preceding claims arranged between said two waveguide layers ( 30 ,  40 ).  
     
     
         16 . Quantum cascade laser in accordance with  claim 15  having means for selecting the wave length of the emitted laser light.  
     
     
         17 . Quantum cascade laser in accordance with  claim 15 , which is connected to a heat sink to dissipate heat generated in the operation of the laser.