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The electronic structure of a prototype dilute magnetic semiconductor (DMS), Ga(1-x)MnxAs, is studied by magnetic circular dichroism (MCD) spectroscopy. We prove that the optical transitions originated from impurity bands cause the strong positive MCD background. The MCD signal due to the E0 transition from the valence band to the conduction band is negative indicating that the p-d exchange interactions between the p carriers and d spin is antiferromagnetic. The negative E0 MCD signal also indicates that the hole doping of the valence band is not so large as previously assumed. The impurity bands seem to play important roles for the ferromagnetism of Ga(1-x)MnxAs.

The problem of preparing high-mobility thin InSb films is revisited for magnetoresistive and spintronic sensor applications. We introduce a growth process that significantly improves the electrical properties of thin unintentionally doped InSb layers ͑60-300 nm͒ epitaxially grown on GaAs͑100͒ substrates by reducing the density of dislocations within the interfacial layer. The epilayer properties are well described by a differential two-layer model. This model confirms that the contribution of the interface can only be donor-like. Moreover, the electrical properties of the InSb layers change continuously away from the interface up to sample thickness of the order of 1 m.

The magneto-optical effect in dilute magnetic semiconductors (DMSs) is directly related to the interaction between the d electrons of the transition metal ions and the s, p electrons of the host semiconductor. We show the advantages of the magneto-optical effect of DMSs as regards fabricating magneto-optical waveguide devices that can be integrated with other semiconductor optical devices. We also discuss the advantages of magneto-optical spectroscopy for characterizing DMSs. Intrinsic ferromagnetism of In 1−x Mn x As, Ga 1−x Mn x As and Zn 1−x Cr x Te is confirmed by using magnetic circular dichroism (MCD) spectroscopy. The MCD analyses also show that Zn 1−x TM x O (TM = Mn, Fe, Co, Ni or Cu), Ga 1−x Mn x N and Ga 1−x Cr x As are paramagnetic DMSs with the s, p-d exchange interaction. Ferromagnetic behaviours observed in some transition metal doped ZnO, GaN and GaAs samples are attributed to unidentified precipitations not detectable by means of x-ray diffraction analysis.