Question

6. (a) Calculate the density of GaAs (the lattice constant of GaAs is 5.65 Å, and the atomic weights of Ga and As are 69.72 and 74.92 g/mol, respectively). (b) A gallium arsenide sample is doped with tin. If the tin displaces gallium atoms in crystal lattice, are donors or acceptors formed? Why? Is the semiconductorn- or p-type?

Answer 1

"a) GaAs has ""Zinc Blend structure, that contains & atoms. Using formula to find crystal density: - rho = number of atoms times atom weight/ avegadro's number times volume (i.e simply derived from density = Mass/Volume) Total mass = number of atoms times atomic weight divided by avegadro's no. of per mole. Given, lattice constant = 5.65 A degree = a GaAs has cubical structure so, volume = a^3 total atom weight = (69.72 + 74.92) = 144.64 g/mol no. of atoms = 4 substituting in rho: \r\n rho = 4 times 144.64/6.022 times 10^26 times (5.65 times 10^-8)^3 g/cc rho = 578.56/1086.14 times 10^26 times 10^-24 = 0.532 times 10^-2 g/cc b) when GaAs sample is doped with T_in (S_n), donors will be formed because T_in(S_n) electronic configuration is S_n = [K_r] 4 d^10 5 s^2 5 p^2 i.e (4 e^- at outer shell) now, if T_in displaces gallium "