We have theoretically investigated the subband structure of single Si delta-doped GaAs inserted into a quantum well at T = 0 K. We will discuss the influence of the delta-doping concentration, the delta-layer thickness and diffusion of donor impurities. The spread of the impurities are taken into account in two different models: (i) a uniform distribution and (ii) a nonuniform distribution. In this paper, the nonuniform distribution is different from the Gaussian distribution use of other authors. The electronic structures have been calculated by solving the Schrodinger and Poisson equations self-consistently. We thus find the confining potential, the subband energies and their eigen envelope functions, the subband occupations and Fermi energy. (C) 2000 Academic Press.