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Unformatted text preview: ECE 340 Homework XVIII Fall 2003 Due: Wednesday, December 10, 2003 1. Refer to Fig. 113. Assuming the lattice constant varies linearly with composition x for a ternary alloy, what composition of GaSb1xAsx is latticematched to InP? What composition of InxGa1xP is lattice matched to GaAs? What is the bandgap energy in each case? Also, assuming that a pn junction is made in the corresponding latticematched epitaxial layer and light emits in each case, which substrate is considered to be transparent? Namely, which substrate would not considerably absorb the light emitted from the pn junction toward the substrate? Solutions: For GaSb 1x As x , the lattice constants are: GaAs: 5.66Å, GaSb: 6.09 Å, InP: 5.87 Å. 6.09 5.87 5.87 5.66 1 x x − − = − , therefore: 0.51 x = At 0.51 x = , GaSb 1x As x has 0.77 g E eV ≈ . Since this E g is smaller than the E g of InP, the light emitted from GaSb 1x As x can’t be absorbed by InP, therefore, the substrate will be transparent to the light emitted from GaSb 1x As x. For In x Ga 1x P, the lattice constants are: InP: 5.87Å, GaP: 5.46Å, GaAs: 5.66 Å. 5.66 5.46 5.87 5.66 1 x x − − = − , therefore: 0.49 x = At 0.49 x = , In x Ga 1x P has 1.95 g E eV ≈ . Since this E g is larger than the E g of GaAs, the light emitted from In x Ga 1x P can be absorbed by GaAs, therefore, the substrate will not be transparent to the light emitted from In...
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 Fall '03
 Lebutron
 Photon, Light, Solar cell, GaAs

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