Hybrid mocvd/mbe epitaxial growth of high-efficiency lattice-matched multijunction solar cells

Abstract

Semiconductor devices and methods of fabricating semiconductor devices having a dilute nitride layer and at least one semiconductor material overlying the dilute nitride layer are disclosed. Hybrid epitaxial growth and the use of aluminum barrier layers to minimize hydrogen diffusion into the dilute nitride layer are used to fabricate high-efficiency multijunction solar cells.

1 . A method of forming a multijunction solar cell, the method comprising:
 depositing a first subcell using molecular beam epitaxy (MBE), wherein the first subcell comprises a first base layer, the first base layer comprises dilute nitride;   depositing an aluminum-containing hydrogen-diffusion barrier layer using MBE, the aluminum-containing hydrogen-diffusion barrier overlying the first subcell;   depositing a first tunnel junction using metal-organic chemical vapor deposition (MOCVD); and   depositing a second subcell using MOCVD, the second subcell overlying the first tunnel junction.   
     
     
         2 . The method of  claim 1 , wherein the dilute nitride of the first base layer comprises GaInNAsSb, GaInNAsBi, GaInNAsSbBi, GaNAsSb, GaNAsBi, or GaNAsSbBi. 
     
     
         3 . The method of  claim 1 , wherein depositing the second subcell comprises depositing a second base layer, the second base layer comprising (In)GaAs. 
     
     
         4 . The method of  claim 1 , further comprising:
 depositing a second tunnel junction using MOCVD, the second tunnel junction overlying the second subcell; and   depositing a third subcell using MOCVD, the third subcell overlying the second tunnel junction.   
     
     
         5 . The method of  claim 4 , further comprising:
 depositing a top contact layer using MOCVD, the top contact layer overlying the third subcell.   
     
     
         6 . The method of  claim 4 , wherein the second subcell comprises GaAs, and the third subcell comprises AlInGaP. 
     
     
         7 . The method of  claim 1 , further comprising:
 depositing a second tunnel junction using MBE, the second tunnel junction underlying or overlying the first subcell.   
     
     
         8 . The method of  claim 1 , further comprising:
 depositing a third subcell using MOCVD, the third subcell overlying the aluminum-containing hydrogen-diffusion barrier layer.   
     
     
         9 . The method of  claim 1 , further comprising:
 depositing an emitter overlying the first base layer, wherein the emitter does not comprise aluminum,   wherein the aluminum-containing hydrogen-diffusion barrier layer is overlying the emitter.   
     
     
         10 . The method of  claim 1 , wherein the first subcell is deposited overlying a substrate, the substrate comprising Ge or GaAs. 
     
     
         11 . The method of  claim 1 , further comprising:
 depositing a semiconductor layer using MBE, the semiconductor layer comprising GaAs, InGaAs, or InGaP.   
     
     
         12 . The method of  claim 1 , further comprising:
 depositing a buffer layer, the buffer layer underlying the first subcell; and   depositing a nucleation layer using MOCVD, the nucleation layer underlying the buffer layer.   
     
     
         13 . The method of  claim 12 , wherein a first portion of the buffer layer is deposited using MOCVD, and a second portion of the buffer layer is deposited using MBE. 
     
     
         14 . The method of  claim 1 , wherein the dilute nitride of the first base layer comprises GaInNAsSb,
 wherein the first base layer has a background doping concentration less than 10 16  cm −3 , is lattice-matched to GaAs or Ge, has a hydrogen-induced defect density less than the background doping concentration, has a band gap from 0.7 to 1.2 eV, and does not comprise aluminum.   
     
     
         15 . The method of  claim 1 , wherein the aluminum-containing hydrogen-diffusion barrier layer comprises AlGaAs, AlGaAsSb, AlGaAsBi, AlInP, AlInGaP, AlInGaPSb, AlInGaPBi, AlInGaAs, AlInGaAsSb, AlInGaAsBi, AlN, AlNSb, or AlNBi, has a thickness from 100 nm to 500 nm, and comprises an aluminum alloy, the aluminum alloy having an aluminum content within a range from 35 mol % to 45 mol %, wherein mol % is based on the fraction of group-III atoms in the aluminum alloy. 
     
     
         16 . The method of  claim 1 , wherein first tunnel junction comprises one or more of:
 GaAs, AlGaAs, InGaAs, and GaInP.   
     
     
         17 . The method of  claim 1 , further comprising:
 depositing an aluminum-free layer, the aluminum-free layer adjacent to the aluminum-containing hydrogen-diffusion barrier layer.   
     
     
         18 . The method of  claim 1 , wherein depositing the aluminum-containing hydrogen-diffusion barrier layer comprises depositing a reflector, wherein the reflector comprises alternating layers of materials having different refractive indices. 
     
     
         19 . The method of  claim 18 , wherein a first portion of the reflector is deposited using MBE, and a second portion of the reflector is deposited using MOCVD. 
     
     
         20 . The method of  claim 1 , wherein the aluminum-containing hydrogen-diffusion barrier layer has a thickness between 100 nm and 5 microns.