Optical properties of diluted magnetic semiconductors: I. Magnetooptics. II. Inelastic light scattering

Eunsoon Oh, Purdue University

Abstract

Faraday effect in the wurtzite (uniaxial) diluted magnetic semiconductor (DMS), Cd$\sb{\rm 1-x}$Mn$\sb{\rm x}$Se, is studied with the magnetic field (H) either parallel or perpendicular its optic axis (c). For H$\Vert$c, the Faraday effect is qualitatively similar to that in the cubic DMS's. The Faraday rotation, positive for CdSe, becomes negative and very large when Mn$\sp{2+}$ replaces Cd$\sp{2+}$. The sign of the rotation and its dependence on x, H, and temperature T are dominated by the spin-spin exchange interaction between band electrons and Mn$\sp{2+}$ electrons (sp-d exchange interaction). The dispersion of the Faraday effect is well described by an excitonic model. The antiferromagnetic coupling between Mn$\sp{2+}$ ions is manifested in the Faraday effect through the phenomenological effective temperature (T+T$\sb{\rm AF}$), as well as with hysteresis effects associated with the formation of spin-glass phase for high x and low T. For H$\bot$c, the natural birefringence of Cd$\sb{\rm 1-x}$Mn$\sb{\rm x}$Se as well as the Faraday rotation affects the polarization of the light. Decomposing the combined effect into the separate contributions due to the birefringence and the Faraday effect, it is found that the dispersion of the Faraday constant is very similar for H$\bot$c and H$\Vert$c, although the Faraday effect for the former is smaller. In the Voigt geometry (H$\bot$k), the refractive index parallel to H differs from that perpendicular to H, resulting in a linear double refraction, called the Voigt effect. This effect is found to be very large in the DMS's due to the large sp-d exchange interaction. An excitonic model describes the dispersion and H$\sp2$-dependence of the Voigt effect in Cd$\sb{\rm 1-x}$Mn$\sb{\rm x}$Te. The Voigt effect in Cd$\sb{\rm 1-x}$Mn$\sb{\rm x}$Se shows an anisotropy due to the crystal field splitting presented in the wurtzite DMS's. The Raman scattering in a II-VI quaternary (Cd$\sb{\rm 1-x-y}$Zn$\sb{\rm x}$Mn$\sb{\rm y}$Te) exhibits vibrational excitation, the composition dependence of the frequencies of the zone-center optical phonons being amenable to an extension of the modified random-element isodisplacement model. As a member of DMS alloys Cd$\sb{\rm 1-x-y}$Zn$\sb{\rm x}$Mn$\sb{\rm y}$Te exhibits the pronounced magnetic-field dependence of the excitonic photoluminescence, Raman-electron paramagnetic resonance of Mn$\sp{2+}$, and evidence of Raman-antiferromagnetic resonance.

Degree

Ph.D.

Advisors

Ramdas, Purdue University.

Subject Area

Condensation|Optics

COinS