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Dielectric and Magnetic Birefringence in Zn Mn Se Dielectric And DielectricDielectric andand magneticmagnetic birefringencebirefringence inin ZnZn1-x1-xMnMnxxSeSe M. F. Saenger1,2,*, D. J. Sellmyer2, R. D. Kirby2, T. Hofmann1,2, and M. Schubert1,2 1 Department of Electrical Engineering, University of Nebraska-Lincoln, 68588, U.S.A. ellipsometry.unl.edu 2 Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588, USA *[email protected] Introduction Results Experiment Interaction between long wavelength electromagnetic σ σ incident reflected radiation and bound and unbound electrical charge x = 0.00 x = 0.14 + − coil coil Formation of wurtzite planes normal Γ |+1/2> light light carriers subjected to an external magnetic field causes The underlying mechanism of the giant Faraday 6 |-1/2> to the [111] direction causes optical birefringence precisely measurable using effect is the interaction between the spin of the [111] dielectric birefringence in dependance localized 3d5-electrons of the Mn ions and the m Ф generalized ellipsometry. ZnSe is an important II-VI of J mirror band electrons. When µ0H ≠ 0, the conduction semiconductor with a variety of applications in |-1/2> µ H the Mn concentration x. At x = 0.3 a and valence bands split, which is known as 0 θ optoelectronic devices. phase transformation from the |-1/2> sp-d exchange. Γ8 sphalerite to the wurtzite structure |+1/2> sample Litvinov |+1/2> x [110] occurs. 2007 ZnSe oxide 10 nm Zn Mn Se ... 1-x x Zn1-xMnxSe Zn, Mn Se Optical detection and quantification of anisotropy GaAs (001) bulk MO birefringence possesses a temperature dependent magnetic 0.04 M /M x = 0.28 23 11 x moment as well as remarkable magnetooptic (MO) Mn M13 spectra for •Change due to the sp-d properties, which in conjunction with the two different 0.28 0.03 interaction. z [001] μ0H electronic properties suggest future applications sample for MO and spintronic devices. orientations. •The dielectric anisotropy is θ = 135°, 180° 0.02 0.13 taken into account when x = 0.13 modeling the MO effect. 0.01 0.02 Maximum Mueller matrix birefringence Dielectric tensor model detected for x = 0.13 0.00 0.00 1.52.02.53.0 The oscillations Generalized Ellipsometry measures the general optical polarization Photon energy (eV) depend on the layer response of samples in terms of Mueller matrix elements, and allows thickness. for reconstruction of the permittivity, permeability, and magneto- x = 0.02 electric response tensors. ⊥ ⊥ θ = 135° M /M θ = 0° ⎛(ρ + ρ ) i(ρ +- ρ ) 0 ⎞ 0.01 23 11 + − + − θ = 45 ° The dielectric anisotropy influences ⎜ ⎟ No birefringence The Mueller matrix elements Mij Sensitive to chiral 1 ⊥ ⊥ the MO birefringence ε (E) = ⎜i(ρ +- ρ ) (ρ + ρ ) 0 ⎟ detected for x = connect incident and emergent anisotropy + − + − 0.02 or lower. real-valued Stokes vector (magnetic 2 The MO birefringence depends also ⎜ // // ⎟ 0.00 components: birefringence) ⎝ 0 0 (ρ+ + ρ− )⎠ on the orientation of the sample. Therefore it is necessary to have a S = I + I S M M M M S μ H = 0 p s ⎡ 0 ⎤ ⎛ 11 12 13 14 ⎞⎡ 0 ⎤ 8.5 1.5 0 model which takes this effect properly ⎢ ⎥ ⎜ ⎟⎢ ⎥ 1.8 T x = 0.28 into account. S1 = I p − I s S M M M M S ⎢ 1 ⎥ ⎜ 21 22 23 24 ⎟⎢ 1 ⎥ Continuum- -0.01 = ⎜ ⎟ E and E +Δ Discrete Higher energy ⊥ S2 = I45 − I−45 ⎢S ⎥ M M M M ⎢S ⎥ 0 0 0 exciton E 2.4 2.6 2.8 3.0 2 ⎜ 31 32 33 34 ⎟ 2 transitions excitons at CP transitions 8.0 0 ⎢ ⎥ ⎜ ⎟⎢ ⎥ transitions The formation of Photon energy (eV) S3 = Iσ + − Iσ − S M M M M S E0 and E0+Δ0 ⊥ ⎣ 3 ⎦output ⎝ 41 42 43 44 ⎠⎣ 3 ⎦input 2 E wurtzite planes in 0 1.0 0 the [111] direction 7.5 // E0 -2 Highly sensitive to dielectric } } causes an energy j j The diagonal elements of ε // ε -4 { { birefringence. band gap shift E0 the dielectric tensor can -6 between the Re Im Re(ε ) × 1000 7.0 be obtined. The sample xy optical axis 2.6 2.7 with highest magnetic 0.5 parallel (||) and 6 x = 0.02 ε × Loss-less Im( xy) 1000 3-Dim birefringence is also the Our message Lorentzian line dispersion Lorentz perpendicular () x = 0.13 M type CP oscillator 4 0 pole to the [111] 6.5 sample with highest Mn x = 0.28 2 direction. x = 0.13 concentration. 0 6.0 0.0 1.8 2.1 2.4 2.7 We studied the dielectric and magnetic-field induced v c c v 1.5 2.0 2.5 3.0 anisotropic optical properties of Zn Mn Se thin films with h Photon Energy (eV) Photon energy (eV) 1-x x Ei (mJ → mJ ) = Ei + (ω0 +ω0 ) + generalized spectroscopic ellipsometry in the VIS-UV 2 Landau spectral range for Mn concentrations of x = 0.00, 0.02,0.13 and 0.28. The dielectric and the magnetic field induced c v anisotropies in Zn1-xMnxSe were treated separately into the + (m g − m g )μ H + The dielectric anisotropy can be The ellipsometric model allows us to diagonal and off-diagonal components of the dielectric J J 0 Zeeman measured in terms of the energy band measure the spd-exchange energy and tensor. c c v gap shift Landau shift. We are able to quantify the shift of the band gap energy + [EJ (mJ ) − E(mJ )] // ⊥ ⊥ // E (±3/ 2) − E (±1/ 2) sp-d exchange xMn E0 E0 E0 - E0 xMn c v EL −4 −4 between the DF parallel and perpendicular to the optical axis eV eV meV 1×10 eV 1×10 eV caused by the formation of wurtzite domains with increasing μ0H x. E 0.13 2.6491 (7) 2.6549 (5) 5.8 (9) 0.02 2 (1) 1.1 (3) - 0.28 2.6743 (5) 2.6784 (6) 4.1 (8) 0.13 8 (3) 1.2 (5) q , me The optical anisotropy occurs in the direction [111], which is 0.28 12 (3) 1.0 (4) in good concordance with previous TEM investigations. The dielectric anisotropy results in a red shift of the energy band The anisotropy is not proportional to the Loop measurements in dependance of gap parallel to the optical axis with a maximum for x = 0.13. Mn concentration x. For x closer to 0.13 the magnetic field can also be modeled. the anisotropy reaches at least one Measurements of the sp-d exchange energy at room MRSEC Q-SPINS Meeting, Lincoln, NE, October 5, 2007 maximum. temperature are presented and found a maximum value for 54th Midwest Semiconductor Conference, Lincoln, NE, October 6-7, 2007 the sample with maximum Mn concentration x = 0.28..
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