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Unformatted text preview: ECE 340 Homework XVIII Fall 2003 Due: Wednesday, December 10, 2003 1. Refer to Fig. 1-13. Assuming the lattice constant varies linearly with composition x for a ternary alloy, what composition of GaSb1-xAsx is lattice-matched to InP? What composition of InxGa1-xP is lattice- matched to GaAs? What is the bandgap energy in each case? Also, assuming that a p-n junction is made in the corresponding lattice-matched 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 p-n junction toward the substrate? Solutions: For GaSb 1-x As x , the lattice constants are: GaAs: 5.66, GaSb: 6.09 , InP: 5.87 . 6.09 5.87 5.87 5.66 1 x x = , therefore: 0.51 x = At 0.51 x = , GaSb 1-x 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 1-x As x cant be absorbed by InP, therefore, the substrate will be transparent to the light emitted from GaSb 1-x As x. For In x Ga 1-x P, the lattice constants are: InP: 5.87, GaP: 5.46, GaAs: 5.66 . 5.66 5.46 5.87 5.66 1 x x = , therefore: 0.49 x = At 0.49 x = , In x Ga 1-x 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 1-x 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