  In the present paper, we study the diffusion limit of the classical solution
to the Vlasov-Poisson-Fokker-Planck (VPFP) system with initial data near a
global Maxwellian. We prove the convergence and establish the optimal
convergence rate of the global strong solution to the VPFP system towards the
solution to the drift-diffusion-Poisson system based on the spectral analysis
with precise estimation on the initial layer.
