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In monolithic MJ devices, each semiconductor layer is grown on top of one another. However, if the lattice constants of the crystals in adjacent layers do not match this will result in lattice strain and potentially dislocations. These dislocations cause defects to form in the crystal structure leading to unwanted recombinations and subsequently a decrease in cell efficiency. For this reason, it is advantageous to select semiconductor materials that have matching or closely similar lattice constants. Figure 5 shows a list of common MJ semiconductors and their lattice constants. The turquoise lines indicate the lattice constants for mixtures of the two connected materials. | In monolithic MJ devices, each semiconductor layer is grown on top of one another. However, if the lattice constants of the crystals in adjacent layers do not match this will result in lattice strain and potentially dislocations. These dislocations cause defects to form in the crystal structure leading to unwanted recombinations and subsequently a decrease in cell efficiency. For this reason, it is advantageous to select semiconductor materials that have matching or closely similar lattice constants. Figure 5 shows a list of common MJ semiconductors and their lattice constants. The turquoise lines indicate the lattice constants for mixtures of the two connected materials. | ||
[[File:Latticeconstants.JPG|center|thumb|Figure 5: Lattice constants of semiconductor alloys (Román, 2004 | [[File:Latticeconstants.JPG|center|thumb|Figure 5: Lattice constants of semiconductor alloys (Román, 2004]] | ||
It can be seen that few materials have perfectly aligned lattice constants. For this reason, lattice-mismatched, or metamorphic{{W|metamorphic}}, MJ cells are starting to be developed as this allows for a much greater degree of freedom in semiconductor selection. The potential for metamorphic cells lies in the ability of manufacturers to utilize cheaper materials that also possess band gaps near the optimal values for maximum theoretical efficiency. In certain cases, these benefits will outweigh the recombination losses due to lattice mismatch. | It can be seen that few materials have perfectly aligned lattice constants. For this reason, lattice-mismatched, or metamorphic{{W|metamorphic}}, MJ cells are starting to be developed as this allows for a much greater degree of freedom in semiconductor selection. The potential for metamorphic cells lies in the ability of manufacturers to utilize cheaper materials that also possess band gaps near the optimal values for maximum theoretical efficiency. In certain cases, these benefits will outweigh the recombination losses due to lattice mismatch. |