ZnO gap states investigated using magnetic circular dichroism

Abstract

We investigate gap states in a series of nonmagnetic ZnO films grown by molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) using magnetic circular dichroism. This technique is shown to be sensitive enough to investigate defect states in thin films of disordered wide-gap semiconductors by differentiating between a loss of transmission due to scattering and absorption. The method is first applied to Zn-and O-terminated films grown by MBE. The O-terminated film shows a broad peak centred at ~2.4 eV which corresponds to the green PL signal, whereas the Zn-terminated film shows a magnetic circular dichroism (MCD) signal that increases slowly with energy. The method was then extended to PLD films. Oxygen vacancy states in both MBE and PLD-grown films were identified, and the introduction of low concentrations of Al was shown to quench the MCD signal at low energy by neutralising the paramagnetic oxygen vacancies. In PLD-grown ZnAlO we observed a negative MCD that increased in magnitude as the energy approached the band edge indicating a much more pronounced spin-split impurity and conduction band. These examples illustrate the versatility of the MCD technique in identifying gap states in a variety of different types of ZnO samples.

On the Origin of d0 Magnetism in Transparent Metal Oxide Nanocrystals

“…Although the sample synthesized in the oxidizing environment can still contain zinc vacancies, they do not exhibit any Curie-type behavior. The local magnetic moment in ZnO NCs has been attributed to either oxygen or zinc vacancy sites, ,,− as determined by electron paramagnetic resonance (EPR) or X-ray MCD spectroscopies. These sites are also the most thermodynamically stable point defects in the wurtzite ZnO lattice .…”

Investigation of the distribution of localised and extended states in amorphous MoOx

“…25,26 The measurements were taken at room temperature in an applied magnetic field of 1.8 T and we detect a signal from the occupied states that are spin polarised by this applied magnetic field. 27 The upper limit of the energy on our MCD plots was determined by the point where the films begin to absorb strongly; at this point the total transmitted intensity is too low, and we cannot record the MCD accurately. The data from the sapphire substrates was also recorded.…”

Synthesis and characterization of Dy 3 Fe 5 O 12 nanoparticles fabricated with the anion resin exchange precipitation method

“…The series of works of G.A. Gehring with co-authors are known devoted to the MCD study of the manganite, magnetite, ZnO, and doped ZnO thin films (e.g., [18,19]). As concerns rare earth iron-garnet ferrites, number of authors investigated the Faraday rotation (FR) in a variety of magnetically ordered bulk garnet crystals and films (for instance, [20,21,22]).…”