Barrier potential, E> V0
V(X) = 0 ( x < 0 )
= V0 ( 0 < x < a )
= 0 ( x> a )
Psi(x)1 = Aexp[ik1x] + B exp[-ik1x]
Psi(x)2 = Cexp[ik2x] + D exp[-ik2x]
Psi(x)3 = Fexp[ik1x] + G exp[-ik1x] ( K3= K1 so I put k1 )
and G = 0 because there is no reflection,
I used B.C...