The light sources used in fiber-optic communication are made of GaP film sandwiched between
GaAs. The cubic lattice constants are $a_{GaP} = 6.45 \AA$ and $a_{GaAs} = 5.65 \AA$, and $\nu \approx 0.3$ for GaP. (a)
If grown on a bulk GaAs(001) substrate, evaluate the strained lattice parameters of GaP
pseudomorphic film.
(b) Draw the cross-section schematic lattice diagram near the interface when the GaP film is
relaxed.
(c) Draw a schematic diagram and describe briefly the nucleation and gliding of dislocations in
the relaxed GaP film, and explain the formation of threading dislocations.
(d) What can be done in order to get a relaxed GaP film with extreme low threading dislocation
density?
