To find u (x) in each region, we need to manipulate the electron's wavefunction: ψ ψ ( 0 < x < a − − b ) = A e i α α x + A ′ e − − i α α x = e i k x ( A e i ( α α − − k ) x + A ′ e − − i ( α α + k ) x ) ⇒ ⇒ u ( 0 < x < a − − b ) = A e i ( α α − − k ) x + A ′ e − − i ( α α + k ) x .