1. Gallium arsenide (GaAs) has a complex face-centered cubic (FCC) crystal struc

Question

1. Gallium arsenide (GaAs) has a complex face-centered cubic (FCC) crystal structure with tetrahedral bonding between atoms and half of its tetrahedral sites filled. If its lattice parameter is 5.65 x 10^-8 cm,

(a) Calculate its atom density (number of atoms per cm^3)?

(b) What are two different positions that the Ga atoms and As atoms can occupy in the complex FCC crystal structure? Explain.

(c) Suppose all the tetrahedral sites in the lattice were filled, how many atoms would be in the crystal structure?

Explanation / Answer

c) If all the tetrahedral sites were filled, total number of atoms in unit cell = 12

a) volume of the lattice = (5.65*10-8)3 = 1.8*10-22 cm3

Total number of atoms in lattice point = 4

Number of tetrahedral sites filled = 4

Number of atoms in the lattice = 8

Thus, atom density = 8/(1.8*10-22) = 4.435*1022 atoms/cm3

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