Low bandgap, monolithic, multi-bandgap, optoelectronic devices

Abstract

Low-bandgap, monolithic, multi-bandgap, optoelectronic devices ( 10 ), including PV converters, photodetectors, and LED's, have lattice-matched (LM), double-heterostructure (DH), low-bandgap GaInAs(P) subcells ( 22, 24 ) including those that are lattice-mismatched (LMM) to InP, grown on an InP substrate ( 26 ) by use of at least one graded lattice constant transition layer ( 20 ) of InAsP positioned somewhere between the InP substrate ( 26 ) and the LMM subcell(s) ( 22, 24 ). These devices are monofacial ( 10 ) or bifacial ( 80 ) and include monolithic, integrated, modules (MIMs) ( 190 ) with a plurality of voltage-matched subcell circuits ( 262, 264, 266, 270, 272 ) as well as other variations and embodiments.

1 . A monolithic, multi-bandgap, photovoltaic converter, comprising: 
 a first subcell comprising GaInAs(P) with a first bandgap and a first lattice constant;    a second subcell comprising GaInAs(P) with a second bandgap and a second lattice constant, wherein the second bandgap is less than the first bandgap and the second lattice constant is greater than the first lattice constant, and further, wherein the second lattice constant is equal to a lattice constant of a InAs y P 1-y  alloy with a bandgap greater than the first bandgap; and    a lattice constant transition material positioned between the first subcell and the second subcell, said lattice constant transition material comprising InAs y P 1-y  alloy with a lattice constant that changes gradually from the first lattice constant to the second lattice constant.    
     
     
         2 . The monolithic, multi-bandgap, photovoltaic converter of  claim 1 , wherein the lattice constant transition material is grown epitaxially on the first subcell with a gradually increasing value for y.  
     
     
         3 . The monolithic, multi-bandgap, photovoltaic converter of claim w, wherein the second subcell is grown epitaxially on the lattice constant transition material.  
     
     
         4 . The monolithic, multi-bandgap, photovoltaic converter of  claim 1 , wherein the first subcell is a lattice-matched, double-heterostructure, comprising homojunction layers of GaInAsP) clad by InAs y P 1-y  cladding layers wherein the InAs y P 1-y  cladding has a value for y in a range of o≦y<1, such the InAs y P 1-y  cladding layers of the first subcell have a lattice constant equal to the first lattice constant.  
     
     
         5 . The monolithic, multi-bandgap, photovoltaic converter of  claim 4 , wherein the second subcell is a lattice-matched, double-heterostructure comprising homojunction layers of GaInAs(P) clad by InAs y P 1-y  cladding layers, wherein the InAs y P 1-y  cladding has a value for y in a range of o≦y<1, such that the InAs y P 1-y  cladding layer of the second subcell have a lattice constant equal to the second lattice constant.  
     
     
         6 . The monolithic, multi-bandgap, photovoltaic converter of  claim 1 , including a InP substrate, and wherein the first subcell is grown epitaxially on the InP substrate.  
     
     
         7 . The monolithic, multi-bandgap, photovoltaic converter of  claim 1 , including a tunnel junction positioned between the first subcell and the second subcell.  
     
     
         8 . The monolithic, multi-bandgap, photovoltaic converter of  claim 7 , wherein the tunnel junction is positioned between the first subcell and the lattice constant transition layer.  
     
     
         9 . The monolithic, multi-bandgap, photovoltaic converter of  claim 1 , wherein the lattice constant of the lattice constant transition material is graded.  
     
     
         10 . The monolithic, multi-bandgap, photovoltaic converter of  claim 1 , wherein the lattice constant of the lattice constant transition material changes in steps of multiple, discrete, increments.  
     
     
         11 . The monolithic, multi-bandgap, photovoltaic converter of  claim 1 , wherein the first bandgap is 0.74 eV.  
     
     
         12 . The monolithic, multi-bandgap, photovoltaic converter of  claim 6 , wherein the first subcell is grown epitaxially on a front surface of the InP substrate, the lattice constant transition layer is grown epitaxially on a back surface of the InP substrate, and the second subcell is grown epitaxially on the lattice constant transition layer.  
     
     
         13 . The monolithic, multi-bandgap, photovoltaic converter of  claim 12 , wherein the InP substrate is doped with deep acceptor atoms to make the substrate more electrically insulating than InP, which is not doped with deep acceptor atoms.  
     
     
         14 . The monolithic, multi-bandgap, photovoltaic converter of  claim 1 , including a InP substrate positioned between the first subcell and the second subcell.  
     
     
         15 . The monolithic, multi-bandgap, photovoltaic converter of  claim 14 , wherein the InP substrate is positioned between the first subcell and the lattice constant transition material.  
     
     
         16 . The monolithic, multi-bandgap, photovoltaic converter of  claim 1 , including an isolation layer positioned between the first subcell and the second subcell.  
     
     
         17 . The monolithic, multi-bandgap, photovoltaic converter of  claim 16 , wherein the isolation layer is positioned between the first subcell and the lattice constant transition material.  
     
     
         18 . The monolithic, multi-bandgap, photovoltaic converter of  claim 16 , including a InP substrate positioned between the first subcell and the second subcell.  
     
     
         19 . The monolithic, multi-bandgap, photovoltaic converter of  claim 18 , wherein the InP substrate is positioned between the second subcell and the isolation layer.  
     
     
         20 . The monolithic, multi-bandgap, photovoltaic converter of  claim 18 , wherein the InP substrate is positioned between the first subcell and the isolation layer.  
     
     
         21 . The monolithic, multi-bandgap, photovoltaic converter of  claim 14 , including a first isolation layer positioned between the InP substrate and the first subcell, and including a second isolation layer positioned between the InP substrate and the second subcell.  
     
     
         22 . A monolithic, multi-bandgap, photovoltaic converter, comprising: 
 a InP substrate with a substrate lattice constant;    a first subcell comprising GaInAs(P) with a first bandgap and a first lattice constant, wherein the first lattice constant is greater than the substrate lattice constant;    a lattice constant transition material positioned between the InP substrate and the first subcell, said lattice constant transition material comprising InAs y P 1-y  alloy with a lattice constant that changes from the substrate lattice constant to the first lattice constant; and    a second subcell comprising GaInAs(P) positioned behind the first subcell, said GaInAs(P) of the second cell having a second bandgap, which is less than the first bandgap, and a second lattice constant.    
     
     
         23 . The monolithic, multi-bandgap, photovoltaic converter of  claim 22 , wherein the second lattice second lattice constant is equal to the first lattice constant.  
     
     
         24 . The monolithic, multi-bandgap, photovoltaic converter of  claim 23 , including a tunnel junction positioned between the first subcell and the second subcell.  
     
     
         25 . The monolithic, multi-bandgap, photovoltaic converter of  claim 23 , including an isolation layer positioned between the first subcell and the second subcell.  
     
     
         26 . The monolithic, multi-bandgap, photovoltaic converter of  claim 22 , wherein the first subcell is a lattice-matched, double-heterostructure comprising homojunction layers of GaInAs(P) clad by InP cladding layers.  
     
     
         27 . The monolithic, multi-bandgap, photovoltaic converter of  claim 22 , wherein the second subcell is a lattice-matched, double-heterostructure comprising homojunction layers of GaInAs(P) clad by InAs y P 1-y  cladding has a lattice constant equal to the second lattice constant.  
     
     
         28 . The monolithic, multi-bandgap, photovoltaic converter of  claim 23 , including: 
 a third subcell behind the second subcell, said third subcell having a third bandgap, which is less than the second bandgap, and a third lattice constant, which is greater than the second lattice constant; and    a second lattice constant transition material positioned between the second subcell and the first subcell, said second lattice constant transition material comprising InAs y P 1-y  alloy with a lattice constant that changes from the second lattice constant to the third lattice constant.    
     
     
         29 . The monolithic, multi-bandgap, photovoltaic converter of  claim 22 , wherein the second lattice constant is greater than the first lattice constant, and including a second lattice constant transition material positioned between the first subcell and the second subcell, said second lattice constant transition material comprising InAs y P 1-y  alloy with a lattice constant that changes from the first lattice constant to the second lattice constant.  
     
     
         30 . A monolithic, integrated, module (MIM), comprising: 
 a plurality of monolithic, multi-bandgap, photovoltaic converters, each of which comprises: (i) a first subcell with a first bandgap and a first lattice constant; (ii) a second subcell with a second bandgap and a second lattice constant, wherein the second bandgap is less than the first bandgap and the second lattice constant is greater than the first lattice constant; and (iii) a lattice constant transition material positioned between the first subcell and the second subcell, said lattice constant transition material having a bandgap at least as large as the first bandgap and a lattice constant that changes from the first lattice constant to the second lattice constant; and    a common substrate with a substrate bandgap and a substrate lattice constant, said common substrate being positioned between the first subcell and the lattice constant transition material of each of the monolithic, multi-bandgap, photovoltaic converters, wherein the substrate bandgap is at least as large as the first bandgap and the substrate lattice constant is equal to the first lattice constant.    
     
     
         31 . The monolithic, integrated, module (MIM) of  claim 30 , wherein the first subcells are grown epitaxially on a front side of the substrate, and wherein the lattice constant transition materials and the second subcells are grown epitaxially on a back side of the substrate.  
     
     
         32 . The monolithic, integrated, module (MIM) of  claim 30 , wherein the first subcell comprises GaInAs(P), the second subcell comprises GaInAs(P), the lattice constant transition material comprises InAs y P 1-y , and the substrate comprises InP.  
     
     
         33 . The monolithic, integrated, module (MIM) of  claim 30 , including a tunnel junction positioned between the first subcell and the second subcell of each of the monolithic, multi-bandgap, photovoltaic converters.  
     
     
         34 . The monolithic, integrated, module (MIM) of  claim 33 , wherein the tunnel junction is positioned between the first subcell and the substrate.  
     
     
         35 . The monolithic, integrated, module (MIM) of  claim 30 , including an isolation layer positioned between the first subcell and the second subcell of each of the monolithic, multi-bandgap, photovoltaic converters.  
     
     
         36 . A monolithic, integrated, module (MIM, comprising: 
 a plurality of monolithic, multi-bandgap, photovoltaic converters, each of which comprises: (i) a first subcell with a first bandgap and a first lattice constant; (ii) a second subcell with a second bandgap and a second lattice constant, wherein the second bandgap is less than the first bandgap and the second lattice constant is greater than the first lattice constant; and (iii) a lattice constant transition material positioned between the first subcell and the second subcell, said lattice constant transition material having a bandgap at least as large as the first bandgap and a lattice constant that changes from the first lattice constant to the second lattice constant; and    a common substrate with a substrate bandgap and a substrate lattice constant, said common substrate being positioned between the lattice constant transition material and the second subcell of each of the monolithic, multi-bandgap, photovoltaic converters, wherein the substrate bandgap is at least as large as the first bandgap and the substrate lattice constant is equal to the first lattice constant.    
     
     
         37 . The monolithic, integrated, module (MIM) of  claim 36 , wherein the lattice constant transition layers and the first subcells are grown epitaxially on a front side of the substrate, and wherein the second subcells are grown epitaxially on a back side of the substrate.  
     
     
         38 . The monolithic, integrated, module (MIM) of  claim 36 , wherein the first subcell comprises GaInAs(P), the second subcell comprises GaInAs(P), the lattice constant transition material comprises InAs y P 1-y , and the substrate comprises InP.  
     
     
         39 . The monolithic, integrated, module (MIM) of  claim 36 , including a tunnel junction positioned between the first subcell and the second subcell of each of the monolithic, multi-bandgaps, photovoltaic converters.  
     
     
         40 . The monolithic, integrated, module (MIM) of  claim 39 , wherein the tunnel junction is positioned between the substrate and the second subcell.  
     
     
         41 . The monolithic, integrated, module (MIM) of  claim 36 , including an isolation layer positioned between the first subcell and the second subcell of each of the monolithic, multi-bandgap, photovoltaic converters.  
     
     
         42 . The monolithic, integrated, module (MIM) of  claim 41 , wherein a subcell circuit comprising the first subcells is voltage-matched to a subcell circuit comprising the second subcells.  
     
     
         43 . A method of fabricating a monolithic, multi-bandgap, photovoltaic converter, comprising: 
 growing a first subcell comprising GaInAs(P) epitaxially on an InP substrate in a GaInAs(P) formulation that provides a first bandgap that is less than 1.35 eV and a first lattice constant, which equals in InP lattice constant;    growing a lattice constant transition layer on the first subcell, wherein the lattice constant transition layer comprises InAs y P 1-y  with an increasing proportion of As and a decreasing proportion of P so that lattice constant of the InAs y P 1-y  initially equals the first lattice constant and changes to a second lattice constant, which is greater than the first lattice constant, but also maintaining the proportions of As and P at levels that keep the lattice constant transition layer transparent to infrared radiation energy bands lower than infrared radiation energy that can be absorbed by the first subcell; and    growing a second subcell comprising GaInAs(P) epitaxially on the lattice constant transition layer in a GaInAs(P) formulation that has a lattice constant equal to the second lattice constant and a second bandgap that is less than the first bandgap.    
     
     
         43 . A method of fabricating a monolithic, multi-bandgap, photovoltaic converter, comprising: 
 growing a first subcell comprising GaInAs(P) epitaxially on a front side of an InP substrate in a GaInAs(P) formulation that provides a first bandgap that is less than 1.35 eV and a first lattice constant, which equals an InP lattice constant;    growing a lattice constant transition layer comprising InAs y P 1-y  on a back side of the InP substrate, including increasing proportion of As and decreasing proportion of P so that lattice constant of the InAs y P 1-y  initially equals the lattice constant of the InP substrate and changes to a second lattice constant, which is greater than the first lattice constant, but also maintaining the proportions of As and P at levels that keep the lattice constant transition layer transparent to infrared radiation energy levels that are not absorbable by the first subcell.