In order to realize buried quantum structures using a total vacuum system which consists of low-energy focused ion beam and molecular beam epitaxy systems, the structures with passivation layers are discussed by numerical calculations. It is shown by the calculations that the device can be realized even if the growth-interrupted interfaces are passivated by thin GaAs layers if the thickness of each layer is designed carefully. The effect of growth interruption at the GaAs layer is studied experimentally. It is found that the interface-state density depends on the Si concentration at δ-doped layer.