W. Mac

The s,p-d exchange interaction in GaAs heavily doped with Mn

The exciton splitting induced by the s,p-d exchange interaction in Ga1−xMnxAs (x < 0.001) was studied by polarized magnetoreflectance. Data were taken at 2 K in magnetic fields up to 5T. Combining these results with magnetization data, a value (N0α − N0β) = − (2.3 ± 0.6) eV was obtained for the difference between the s-d and p-d exchange constants. Assuming that N0α ≈ +0.2 eV, the p-d exchange is ferromagnetic, with a magnitude N0β ≈ +2.5 eV. Copyright

Intraband absorption and photocurrent spectroscopy of self-assembled p-type Si/SiGe quantum dots

In infrared transmission and photocurrent spectra of self-assembled SiGe quantum dot samples grown in the Stranski–Krastanow mode at temperatures around T=520 °C different types of transitions are observed: in the transmission experiments, an absorption line due to bound-to-bound transitions is measured whereas the photocurrent spectra are determined by bound-to-continuum transitions. The experimental determination of the energies of both types of transitions for the same sample allows a detailed discussion of the features observed in the spectra as well as an estimate of the average Ge content in the dots.

Magnetic properties of Cd1-xMnxTe and Zn1-xMnxTe epilayers with high concentration of Mn

Field-cooled, zero-field-cooled and remanent magnetization of Cd 1 x Mn x Te, Zn 1-x Mn x Te (0.5 < x ≤ 1.0) epilayers, including the end-point MnTe, were measured as functions of temperature and magnetic field. For all diluted systems (x < 1.0) a spin-glass-like behavior was observed. Irreversible effects, typical for the spin-glass, tend to decrease in magnitude with an increasing Mn concentration and vanish in MnTe. This spin-glass-antiferromagnet transition is gradual. Magnetic phase diagrams of Cd 1-x Mn x Te and Zn 1-x Mn x Te are discussed.

Distribution of Jahn-Teller distortions of Cr2+ in ZnTe from magnetization steps

Abstract Magnetization steps from isolated Cr 2+ ions in ZnTe were observed at low temperatures, in a magnetic field H ‖[001]. The magnitudes of the steps indicate that the distribution of Jahn-Teller distortions in this sample is much closer to the equilibrium distribution than to a frozen distribution, but perfect equilibrium is not achieved.

The s,p-d exchange interaction in Zn1 − xCrxTe diluted magnetic semiconductors

The reflectance in the free exciton range of Zn 1-x Cr x Te(x < 0.001) was measured in magnetic field up to 5 T and T = 2 K. The ferromagnetic type of exciton splitting was observed. Combining the optical data with the magnetization we estimated the p-d exchange constant N 0 β = + 3.6 ± 1.2 eV.

FIR absorption of Zn1−xCrxS

Abstract The energy level structure of Cr2+ in polytypical ZnCrS in applied magnetic fields was studied using far infrared laser and millimeter wave absorption in the energy range 1.4–25 cm−1. The magnetic fields up to 20 T were oriented along the (1 1 1) or (1 1 0) crystal axis. A strong anisotropy of absorption lines is observed. The description of the data is provided by a cubic crystal field model with a static Jahn-Teller distortion included.

Laser FIR magneto-spectroscopy of Zn1−1CrxSe

Abstract The far infrared laser absorption was measured for Zn 1−1 Cr x Se ( x −1 at T=1.8K and magnetic field up to 20 T. Magnetic field was oriented along (100), (110) and (111) crystallographic axes. The spectra show sharp absorption lines, which we attribute to intra-chromium transitions. Pronounced anisotropy is observed. The overall description of the experimental data is provided by simple crystal field model including static, tetragonal Jahn-Teller distortion of the Cr centers.

Influence of local potentials on spin-splitting in diluted magnetic semiconductors

Magnetoreflectance of the free exciton and magnetization in Zn 1-x Mn x Se and Cd 1-x Mn x Te were measured. The difference between s-d and p-d exchange integrals. N 0 α-N 0 β, evaluated within the framework of the mean field and virtual crystal approximations (MFA and VCA), shows strong concentration dependence. This effect, not predicted by the mean field theory, is described within the model of magnetic and chemical disorder in diluted magnetic semiconductors (DMSS).

Intersubband transitions of boron-doped self-assembled Ge quantum dots

Abstract Infrared intersubband absorption and photocurrent investigations of self-assembled Ge quantum dots grown by molecular beam epitaxy in the Stranski–Krastanow mode at temperatures around T=520°C are reported. In transmission experiments, absorption due to bound-to-bound transitions have been observed whereas the photocurrent spectra are determined by bound-to-continuum transitions. Since both types of experiments were performed on the same sample, the transmission and photocurrent spectra can directly be compared and allow a detailed discussion of the energy levels for one and the same set of quantum dots.

The s,p—d exchange interaction of Cd0.997Cr0.003S

The s,p- d exchange interaction of hexagonal CdCrS is studied by means of Raman scattering and exciton magnetoreflectance. Analysis of Raman data yields s-d exchange parameter N 0 α = + 0.21 eV. Combining this parameter with the heavy-hole exciton splitting we evaluated the p-d exchange parameter N 0 β=+ 0.42 eV. The s.p-d exchange parameters are used for interpretation of the exciton splitting in magnetic field for B∥c and B∥c.