Question

5. (3.8) A 10 A think, uniformly sulfur(S)-doped layer is grown on top of a GaAs wafer. The doping concentration of this layer is 1018cm3. The wafer is sealed with a layer of Si3Ns to prevent any outdiffusion, and it is annealed for 60 min at 950°C. Ignore all heavy doping effects. Assume a diffusion coefficient of 3.7x10-13cm2/s. WI (a) Find the sulfur concentration at the surface after the anneal. (b) At what depth would be concentration be 101cm3?

Answer 1

Doping concentration of the layer is 1 0^1 8 c m^- 3 given that sulfur concentration at 9 5 0 degree v doping concentration N P = 1 0^1 8 c m^-3 back ground concentration, N^B = 5 time 1 0^1 8 time required for differing t = 6 0 min different coefficient D = 3 . 7 time 1 0^- 1 3 cm^2/s temperature of anneal T = 9 5 0 degree c Thickness L = 1 0 A degree energy E_A = 3 . 5 e v and bottzman constant k_t = 8 . 6 1 7 time 1 0^- 5 e v/k The diffusion coefficient id given by D = d_0 ex p ^[-sigma A/K_b T t] 3 . 7 time 1 0