It is found that the oscillator strength is spontaneously modulated in most of experimentally accessible ordered superlattices due to grown-in unintentional disorders. Such disorders cause the localization and the real-space separation of the electron and hole wavefunctions. As a result, an ordered superlattice is transformed into a disordered superlattice where the coherence of superlattice states is broken and the oscillator strength is diminished, which is found to be an ubiquitous effect regardless of the potential lineup. We discuss the limitation of ordered superlattices, and the physics and control of the wavefunctions and the oscillator strength are explored by using a deliberately disordered superlattice grown by molecular beam epitaxy (MBE),