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hw18 - substrate 2 A symmetric p-n junction of area 5cm x...

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ECE 440 Homework XVIII Spring 2006 Due: Wednesday, May 03, 2006 1. Refer to Fig. 1-13. Assuming the lattice constant varies linearly with composition x for a ternary alloy, what composition of In x Ga 1-x P is lattice-matched to GaAs? What is the bandgap energy of the In x Ga 1-x P layer? Also, assume that a p-n junction is made in the corresponding lattice-matched epitaxial layer to form a light emitting diode and isotropic light emits. In general, about half of the photons go toward the substrate side. If the In x Ga 1-x P diode can be grafted from its original GaAs substrate onto different substrates, which substrate among GaSb, InP, GaP and SiC is considered to be transparent? Namely, which substrate would not considerably absorb the light emitted from the p-n junction toward the
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Unformatted text preview: substrate? 2. A symmetric p-n junction of area 5cm x 5cm has rectifying I-V characteristics such that I=I th [exp(qV/kT) –1], where I th = 12 nA. Assume that the minority carrier diffusion lengths L n =L p =2 μm in each side of the junction, and the depletion width is 1 μm. Upon solar illumination in a clear day an optical generation rate of 2x10 18 EHP/cm 3 is obtained uniformly at least one diffusion length deep into each side of the neutral region as well as within the depletion region. (a) Calculate the short-circuit current and the open-circuit voltage for this illuminated junction. (b) Plot the I-V curve for this solar cell. Repeat part (a) when some clouds block the sun and the optical generation rate reduces to a half....
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