3) Silicon (Si) is an essential element in semiconductor industry and is used as a substrate (wafer) on which conductive metals like Au,Cu,Pt,Al and Cr are deposited. Recently, gallium ( Ga ) in the form of GaN,GaAs or Ga2O3 has been successully deposited on Si substrates. Assume that Ga is diffused into pure Si wafer at 1100C for 3h. What is the depth below the surface at which the Ga concentration is 1016 atoms /cm3 if the surface concentration is 1018 atoms /cm3 ? Take the value of D at 1100C as D1100=7.01013cm2/sec. (25 points)