Dilute magnetic semiconductors (DMS), such as Cd1−xMnxTe, are excellent hosts for the study of disordered magnetic systems. In these diluted random alloys, neighboring magnetic ions form clusters through short range spin exchange interactions. A number of experiments [1-8] have been devoted to the investigation of the nearest-neighbor (NN) coupled magnetic ion pairs, by measuring the quantized total spin in a field. In (Cd,Mn)Te, the obtained NN exchange constant J1 is -6.1K[7,8]. However, to understand full range of magnetic and optical phenomena in DMS, it is important to explore the behavior of clusters larger than pairs and interactions beyond NN.

We have conducted a systematic study of Ge-Cd1−xMnxTe heterostructures prepared in situ by deposition of polycrystalline Ge onto atomically clean Cd1−xMnx (110) surfaces. We examined by means of high resolution synchrotron radiation photoemission the valence band offset δEv as a function of the substrate composition x (x=0, 0.35, and 0.60) and bandgap Eg (Eg = 1.47, 1.93, and 2.13 eV). We find δEv=0.84±0.10eV in all cases, and no dependence of δEv on the substrate bandgap within experimental uncertainty. This finding indicates that within the range of validity of the transitivity rule, Cd1−xMnx-Cd1−yMny heterojunctions may actually follow the common anion rule.

Epitaxial layers of Cd1−xMnxTe have been grown on CdTe (100) substrates by evaporating a target with a 1.06 µm pulsed laser. The high - quality materials were characterized by photoluminescence spectroscopy (PL) and energy dispersive analysis of x-ray (EDAX). We find that the incorporation of the Mn in the epitaxial layer is about two - thirds of the concentration in the target. A comparison is made to the epitaxial layers grown on CdTe (111) and GaAs (100) substrates.

The near bandgap photoluminescence of ZnSe epilayers grown on GaAs substrates is measured for pressures up to ∼25 kbar using a diamond anvil cell at T = 9 K. The bandgap changes with pressure, dE/dp, for pseudomorphic and nonpseudomorphic films are obtained, and are compared with results for bulk crystalline ZnSe.

The magnetic and electronic properties of some I-VI semiconductors with 3d transition metals other than Mn are presented. For example, the nonzero orbital moment in Fe2+ leads to more complex electronic energy levels than for Mnt ions. In (CdFe)Se, inelastic light scattering experiments demonstrate that the ground state is nonmagnetic (Van Vleck ion), and directly measures the energy spacing between the three lowest levels. For Sc2+ ions the donor level lies above the bottom of the conduction band in the Cd-based materials.

The high field magnetization for Fe based Diluted Magnetic Semiconductors has been calculated. It is shown that the low temperature magnetization displays characteristic steps, related to the nearest neighbour exchange interaction JNN, provided that JNN exceeds a critical value.

We present a study of the low lying energy levels of Fe2+, Co2+, Ni2+ and Cu2+ in diluted magnetic semiconductors such as Cd1−xCoxTe and Cd1−xCoxSe and their counterparts. In the first of these compounds the magnetic ion sits on a site of symmetry Td while in the second the symmetry is trigonal (C3v). We develop a formulation that permits a continuous variation from Td to C3v symmetry. Comparison with experimental data in Cd1−xCoxSe shows that the C3v distortion amounts to about 10% of the crystal potential at the Co2+ site. Our study of the energy spectra of Fe2+ in Td and C3v crystal potentials reveals that, even in the cubic field, the levels exhibit an anisotropy which manifests it- self in an anisotropy of the magnetization, , in the regime in which is not a linear function of the magnetic field . The study includes all the levels in the lowest terms of the (3d)n (n=6,7,8,9) configurations. The calculations are carried out to second order in the spin-orbit interaction and in for the lowest orbital states and to first order in for the excited states. The g-factors of all the levels are obtained including their anisotropy for the Co2+ and Cu2+Γ8states.

In contrast to the bulk diluted magnetic semiconductor (DMS) Cd1−xMnxSe which occurs with the wurtzite structure, its epilayers grown on (001) GaAs substrate by Molecular Beam Epitaxy exhibit the cubic zinc-blende structure. Raman spectroscopy and photoluminescence studies on this novel DMS show (1) a “two-mode” behavior of the zone center optical phonons, (2) the Raman line associated with the spin-flip in the Zeeman split S = 5/2 ground state of Mn2+, and (3) large Raman shifts associated with the spin-flip of donor-bound electrons. The large magnetic field dependence in (3) with saturation at high fields and low temperature shows that the s-d exchange interaction characteristic of DMS's is also manifested strikingly in the zinc-blende phase of Cd1−xMnxSe.

The magnetospectroscopy data of free exciton in hexagonal Cd1−xFexSe are presented for different magnetic field orientation. Combining exciton splitting data with magnetic susceptibility data we estimate p-d exchange integral for CdFeSe valence band.