Elimination of heterojunction band discontinuities by modulation doping

Conduction- or valence-band discontinuities occurring at the junction of two heterogeneous semiconductors can be eliminated by appropriate doping of the interfacial region. We show by analytic and self-consistent calculations that simultaneous modulation doping and parabolic compositional grading result in flat band-edge potentials. The new concept is applied to distributed Bragg reflectors for vertical cavity lasers. The structures grown by molecular-beam epitaxy exhibit significantly lower resistances as compared to step-graded distributed Bragg reflectors.