US2003089392A1PendingUtilityA1

Photovoltaic device

23
Priority: Jul 25, 2001Filed: Sep 19, 2001Published: May 15, 2003
Est. expiryJul 25, 2021(expired)· nominal 20-yr term from priority
Inventors:Carsten RohrKeith W.J. BarnhamNicholas Ekins-DaukesJames P. ConnollyIan M. BallardMassimo Mazzer
H02S 10/30H10F 77/146H10F 10/163H10F 10/17Y02E10/548B82Y 20/00Y02E10/544
23
PatentIndex Score
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Claims

Abstract

A photovoltaic cell to convert low energy photons is described, consisting of a p-i-n diode with a strain-balanced multi-quantum-well system incorporated in the intrinsic region. The bandgap of the quantum wells is lower than that of the lattice-matched material, while the barriers have a much higher bandgap. Hence the absorption can be extended to longer wavelengths, while maintaining a low dark current as a result of the higher barriers. This leads to greatly improved conversion efficiencies, particularly for low energy photons from low temperature sources. This can be achieved by strain-balancing the quantum wells and barriers, where each individual layer is below the critical thickness and the strain is compensated by quantum wells and barriers being strained in opposite directions minimizing the stress. The absorption can be further extended to longer wavelengths by introducing a strain-relaxed layer (virtual substrate) between the substrate and the active cell.

Claims

exact text as granted — not AI-modified
We claim:  
     
         1 . A photovoltaic device having a multiple quantum well portion with alternating tensile strained layers and compressively strained layers, said tensile strained layers and said compressively strained layers having compositions such that a period of one tensile strained layer and one compressively strained layer exerts substantially no shear force on a neighbouring structure.  
     
     
         2 . A photovoltaic device as claimed in  claim 1 , wherein said neighbouring structure is one of: 
 a further period of one tensile strained layer and one compressively strained layer;    a layer of arbitrary doping having the same lattice constant as a substrate; and a substrate.    
     
     
         3 . A photovoltaic device as claimed in  claim 1 , being a crystalline photovoltaic device grown upon a substrate with a substrate lattice constant.  
     
     
         4 . A photovoltaic device as claimed in  claim 3 , wherein at least one of said tensile strained layers or said compressively strained layers is a quantum well having a Group III/V semiconductor composition with a bandgap lower than if said quantum well had a lattice constant equal to said substrate lattice constant.  
     
     
         5 . A photovoltaic device as claimed in  claim 3 , wherein at least one of said tensile strained layers or said compressively strained layers is a barrier having a Group III/V semiconductor composition with a bandgap higher than if said barrier had a lattice constant equal to said substrate lattice constant.  
     
     
         6 . A photovoltaic device as claimed in  claim 1 , wherein said multiple quantum well portion is formed of alternating quantum well layers and barrier layers having a Group III/V semiconductor composition, wherein a period of one quantum well layer and one quantum barrier layer contains at least four different elements and has an average lattice constant substantially matching a neighbouring structure lattice constant.  
     
     
         7 . A photovoltaic device as claimed in  claim 4 , wherein said substrate is InP and said compressively strained layer is In x Ga 1−x As, where x>0.53.  
     
     
         8 . A photovoltaic device as claimed in  claim 5 , wherein said substrate is InP and said tensile strained layer is In x Ga 1−x As 1−y P y , where y>0.  
     
     
         9 . A photovoltaic device as claimed in  claim 8 , wherein y=1 such that said tensile strained layer is GaInP.  
     
     
         10 . A photovoltaic device as claimed in  claim 3 , wherein said substrate is InP and said multiple quantum well portion is formed of layers of Al x Ga 1−x As y Sb 1−y , where 0≦x≦1 and 0≦y≦1.  
     
     
         11 . A photovoltaic device as claimed in  claim 3 , wherein said substrate is GaSb and said multiple quantum well portion is formed of layers of In x Ga 1−x As y Sb 1−y , where 0≦x≦1 and 0≦y≦1.  
     
     
         12 . A photovoltaic device as claimed in  claim 3 , wherein said substrate is GaAs.  
     
     
         13 . A photovoltaic device as claimed in  claim 12 , wherein said multiple quantum well portion is formed of layers of In x Ga 1−x As y P 1−y , where 0≦x≦1 and 0≦y≦1.  
     
     
         14 . A photovoltaic device as claimed in  claim 1 , wherein said multiple quantum well portion is formed upon a virtual substrate composed of a strain relaxed buffer layer having a virtual substrate lattice constant different from a substrate lattice constant of an underlying substrate.  
     
     
         15 . A photovoltaic device as claimed in  claim 14 , wherein said virtual substrate is InP 1−y As y , where 0<y<1, and said substrate is InP.  
     
     
         16 . A photovoltaic device as claimed in  claim 1 , wherein said photovoltaic device is a thermophotovoltaic device.  
     
     
         17 . A photovoltaic device as claimed in  claim 1 , wherein said quantum wells have a bandgap substantially equal to or less than 0.73 eV  
     
     
         18 . A photovoltaic device having a multiple well quantum portion formed upon a virtual substrate having a virtual substrate lattice constant different than a substrate lattice constant of an underlying substrate, wherein said virtual substrate is InP 1−x As x , where 0<x<1, and said substrate is InP.  
     
     
         19 . A photovoltaic device as claimed in  claim 18 , wherein said multiple quantum well portion is formed with alternating tensile strained layers and compressively strained layers, said tensile strained layers and said compressively strained layers having compositions such that a period of one tensile strained layer and one compressively strained layer exerts substantially no shear force on a neighbouring structure.  
     
     
         20 . A photovoltaic device as claimed in  claim 19 , wherein said neighbouring structure is one of: 
 a further period of one tensile strained layer and one compressively strained layer;    a layer of arbitrary doping having the same lattice constant as said virtual substrate; and    said virtual substrate.    
     
     
         21 . A photovoltaic device as claimed in  claim 18 , wherein at least one of said tensile strained layers or said compressively strained layers is a quantum well having a Group III/V semiconductor composition with a bandgap lower than if said quantum well had a lattice constant equal to said substrate lattice constant.  
     
     
         22 . A photovoltaic device as claimed in  claim 18 , wherein at least one of said tensile strained layers or said compressively strained layers is a barrier having a Group III/V semiconductor composition with a bandgap higher than if said barrier had a lattice constant equal to said substrate lattice constant.  
     
     
         23 . A photovoltaic device as claimed in  claim 18 , wherein said multiple quantum well portion is formed of alternating quantum well layers and barrier layers having a Group III/V semiconductor composition, wherein a period of one quantum well layer and one quantum barrier layer contains at least four different elements and has an average lattice constant substantially matching a neighbouring structure lattice constant.  
     
     
         24 . A photovoltaic device as claimed in  claim 21 , wherein said substrate is InP and said compressively strained layer is In x Ga 1−x As, where x is larger than z of In z Ga 1−z As which is lattice-matched to the virtual substrate.  
     
     
         25 . A photovoltaic device as claimed in  claim 23 , wherein said substrate is InP and said tensile strained layer is In x Ga 1−x As 1−y P y , where y>0.  
     
     
         26 . A photovoltaic device as claimed in  claim 25 , wherein y=1 such that said tensile strained layer is GaInP or wherein x=1 such that said tensile strained layer is InAsP  
     
     
         27 . A photovoltaic device as claimed in  claim 18 , wherein said substrate is InP and said multiple quantum well portion is formed of layers of Al x Ga 1−x As y Sb 1−y , where 0≦x≦1 and 0≦y≦1.  
     
     
         28 . A photovoltaic device as claimed in  claim 18 , wherein said substrate is GaSb and said multiple quantum well portion is formed of layers of In x Ga 1−x As y Sb 1−y , where 0≦x≦1 and 0≦y≦1.  
     
     
         29 . A photovoltaic device as claimed in  claim 18 , wherein said substrate is GaAs.  
     
     
         30 . A photovoltaic device as claimed in  claim 29 , wherein said multiple quantum well portion is formed of layers of In x Ga 1−x As y P 1−y , where 0<x<1 and 0<y<1.  
     
     
         31 . A photovoltaic device as claimed in  claim 18 , wherein said photovoltaic device is a thermophotovoltaic device.  
     
     
         32 . A photovoltaic device as claimed in  claim 18 , wherein said quantum wells have a bandgap substantially equal to or less than 0.73 eV  
     
     
         33 . A photovoltaic device having a multiple quantum well portion formed of strained alternating quantum well layers of In x ,Ga 1−x As, where x>0.53, and barrier layers of Ga y In 1−y P, where y>0.  
     
     
         34 . A photovoltaic device as claimed in  claim 33 , wherein said multiple quantum well portion is formed with alternating tensile strained layers and compressively strained layers, said tensile strained layers and said compressively strained layers having compositions such that a period of one tensile strained layer and one compressively strained layer exerts substantially no shear force on a neighbouring structure.  
     
     
         35 . A photovoltaic device as claimed in  claim 34 , wherein said neighbouring structure is one of: 
 a further period of one tensile strained layer and one compressively strained layer;    a layer of arbitrary doping having the same lattice constant as a substrate; and a substrate.    
     
     
         36 . A photovoltaic device as claimed in  claim 33 , being a crystalline photovoltaic device grown upon a substrate layer with a substrate lattice constant.  
     
     
         37 . A photovoltaic device as claimed in  claim 36 , wherein said substrate is InP.  
     
     
         38 . A photovoltaic device as claimed in  claim 33 , wherein said multiple quantum well portion is formed upon a virtual substrate composed of a strain relaxed buffer layer having a virtual substrate lattice constant different from a substrate lattice constant of an underlying substrate.  
     
     
         39 . A photovoltaic device as claimed in  claim 38 , wherein said virtual substrate is InP 1−y As y , where 0<y<1, and said substrate is InP.  
     
     
         40 . A photovoltaic device as claimed in  claim 33 , wherein said photovoltaic device is a thermophotovoltaic device.  
     
     
         41 . A photovoltaic device as claimed in  claim 33 , wherein said quantum wells have a bandgap substantially equal to or less than 0.73 eV.

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