Raman studies on spintronics materials based on wide bandgap semiconductors

Abstract

Structural properties of GaN and ZnO layers doped with magnetic impurities wereinvestigated by Raman scattering. Long-range lattice ordering and local atomicarrangement around magnetic impurities were analysed, and their solubility limit wasconsidered.For this study, GaN layers doped with Mn and Cr, and ZnO layers doped with Coand V were prepared by molecular beam epitaxy and pulsed laser deposition,respectively. ZnO layers codoped with Ga and N were also studied for the purposeof p-type activation. These samples were observed using a Raman microprobeusing visible and deep UV lasers for excitation. The main results are as follows:In Ga1−xMnxN layers, a uniform solid solution was formed for Mn concentration up tox = 1–2%. An impuritymode was observed at 585 cm−1 and assigned to a local vibrational mode of Mn substituting the Ga site. Athigher Mn concentrations, rapid deterioration in lattice ordering occurred.Ga1−xCrxN layers showed goodlattice ordering up to x = 3–5%. The samples showed resonance enhancement of LO-phonon signals when excited by aUV laser at 266 nm (4.7 eV). This indicates the photo-injection of free carriers to a dilutedmagnetic semiconductor.ZnO layers codoped with Ga and N showed many impurity modes due to host lattice defects. A strongsignal at 580 cm−1 showed a characteristic broadening at high concentrations of N and Ga.This suggested the formation of complex centres with N or related defects.Zn1−xCoxO and Zn1−xVxO layers formed uniform solid solutions up to , but precipitation of the secondary phase was observed at . These samples presented common defect modes as observed in codoped samples. Ourresult suggests that the impurity modes in ZnO-based materials can be used as asensitive probe of host lattice defects induced by the impurity incorporation process.