Influence of s,p-d and s-p exchange couplings on exciton splitting in (Zn,Mn)O

This work presents results of near-band gap magnetooptical studies on (Zn,Mn)O epitaxial layers. We observe excitonic transitions in reflectivity and photoluminescence, that shift towards higher energies when the Mn concentration increases and split nonlinearly under the magnetic field. Excitonic shifts are determined by the s,p-d exchange coupling to magnetic ions, by the electron-hole s-p exchange, and the spin-orbit interactions. A quantitative description of the magnetoreflectivity findings indicates that the free excitons A and B are associated with the Gamma_7 and Gamma_9 valence bands, respectively, the order reversed as compared to wurtzite GaN. Furthermore, our results show that the magnitude of the giant exciton splittings, specific to dilute magnetic semiconductors, is unusual: the magnetoreflectivity data is described by an effective exchange energy N_0(beta-alpha)=+0.2+/-0.1 eV, what points to small and positive N_0 beta. It is shown that both the increase of the gap with x and the small positive value of the exchange energy N_0 beta corroborate recent theory describing the exchange splitting of the valence band in a non-perturbative way, suitable for the case of a strong p-d hybridization.Comment: 8 pages, 8 figure

Optical Properties of Manganese Doped Wide Band Gap ZnS and ZnO

Optical properties of ZnMnO layers grown at low temperature by Atomic Layer Deposition and Metalorganic Vapor Phase Epitaxy are discussed and compared to results obtained for ZnMnS samples. Present results suggest a double valence of Mn ions in ZnO lattice. Strong absorption, with onset at about 2.1 eV, is tentatively related to Mn 2+ to 3+ photoionization. Mechanism of emission deactivation in ZnMnO is discussed and is explained by the processes following the assumed Mn 2+ to 3+ recharging.Comment: 17 pages, 4 figures, 32 reference

Wide and ultra-wide bandgap oxides : where paradigm-shift photovoltaics meets transparent power electronics

Oxides represent the largest family of wide bandgap (WBG) semiconductors and also offer a huge potential range of complementary magnetic and electronic properties, such as ferromagnetism, ferroelectricity, antiferroelectricity and high-temperature superconductivity. Here, we review our integration of WBG and ultra WBG semiconductor oxides into different solar cells architectures where they have the role of transparent conductive electrodes and/or barriers bringing unique functionalities into the structure such above bandgap voltages or switchable interfaces. We also give an overview of the state-of-the-art and perspectives for the emerging semiconductor β- GaO, which is widely forecast to herald the next generation of power electronic converters because of the combination of an UWBG with the capacity to conduct electricity. This opens unprecedented possibilities for the monolithic integration in solar cells of both self-powered logic and power electronics functionalities. Therefore, WBG and UWBG oxides have enormous promise to become key enabling technologies for the zero emissions smart integration of the internet of things

Exchange broadening of EPR line in ZnO:Co

We study the X-band EPR spectra of Co²⁺ in single crystalline Zn₁₋xCoxO (x = 0.001–0.075) thin films grown by plasma-assisted molecular beam epitaxy. By analyzing the EPR linewidth behavior we argue that the exchange-narrowing model, usually applied to Mn-based II-VI DMS, fails here and that a combined effect of exchange and dipolar broadening can explain the linewidth variation with Co content and temperature

Magnetic interactions in Zn1-xMnxO studied by electron paramagnetic resonance spectroscopy

49th Annual Conference on Magnetism and Magnetic Materials, Jacksonville, FL, NOV 07-11, 2004International audienceZn1-xMnxO layers with x varying between 0.006 and 0.22, have been prepared by metal-organic chemical-vapor deposition technique and analyzed by electron paramagnetic 2, resonance spectroscopy. The layers show an exchange narrowed single line spectrum of Mn2+ ions; its temperature dependence demonstrates antiferromagnetic coupling with an effective exchange constant of J1/k(B)=-14.9 K. (c) 2005 American Institute of Physics

Optical biopsy of bone tissue: a step toward the diagnosis of bone pathologies

In vivo absorption and reduced scattering spectra of the human calcaneous from 650 to 1000 nm were assessed using a laboratory system for time-resolved transmittance spectroscopy. Measurements were performed on the calcaneous of seven female volunteers ranging from 26 to 82 years of age. The analysis of the absorption spectra, using a linear combination of the key tissue absorbers (bone mineral, water, lipids, oxy- and deoxyhemoglobin), revealed a general decrease in bone mineral content and an increase in lipids with age, which is in agreement with the aging transformations that occur in bone tissues. The scattering spectra were less effective in detecting such changes in older subjects, showing only a minor decrease in the coefficient for these subjects. The capability to noninvasively quantify bone tissue composition suggests a possible use of optical biopsy for the diagnosis of bone pathologies such as osteoporosis, which are characterized by a progressive reduction and transformation of the mineral in the bone matrix

Conductivity type inversion in wide band gap antiferromagnetic FeTiO 3

International audienc

Zn1-xMnxO: A typical member of the II-VI : Mn DMS family

Symposium on ZnO and Related Materials held at the 2006 EMRS Spring Meeting, Nice, FRANCE, MAY 29-JUN 02, 2006International audienceZnO:Mn thin films are grown by MOCVD technique. Mn(x) varies in 0 < x < 0.44 range. Vegrad's law has been verified for the lattice parameters. EPR measurements prove the substitution incorporation of Mn2+ on zinc sites. The behavior of EPR line-width regarding temperature is discussed. All ZnO:Mn layers show antiferromagnetic interaction and a J(1)/k(B) = -15 K effective exchange constant. Observation of excitons, giant Zeeman effect, and trace of the Brillouin function is evidence for high quality of the crystal lattice and of substitutional incorporation of manganese ions in place of Zn, as Mn2+. (c) 2007 Elsevier Ltd. All rights reserved