Fermi level effects on Mn incorporation in modulation-doped ferromagneticIII1−xMnxV heterostructures

Abstract

The effect of increasing the Fermi level by modulation doping on the incorporation ofMn into the III–V host lattice—and hence on the ferromagnetic properties ofIII1−xMnxV alloys—isinvestigated in Ga1−xMnxAs/Ga1−yAlyAs heterojunctions and quantum wells. Introducing Be acceptors into theGa1−yAlyAs barriers leads to an increase of the Curie temperatureTC ofGa1−xMnxAs, from 70 K in undoped structures to over 100 K in modulation-doped structures. Thisincrease is qualitatively consistent with multi-band mean field theory simulation ofcarrier-mediated ferromagnetism. Here the crucial feature is that the increase ofTC occurs only in those structures where the modulation doping isintroduced after the deposition of the magnetic layer, and thatTC actually drops when the Be-doped layer is grown first. Using ion channellingtechniques we provide direct evidence that this latter reduction inTC is directly correlated with an increased formation of magnetically inactive Mn interstitials.This formation of interstitials is induced by the shift of the Fermi energy as theholes are transferred from the barrier to the quantum well during the growth.