Resonant Raman scattering probe of alloying effect in ZnMgO thin films

Abstract

We have presented a detailed resonant Raman scattering investigation for the alloying effect in hexagonal Zn1−xMgxO (x⩽0.323) thin films grown by pulsed laser deposition. Alloy-induced longitudinal optical (LO) phonon resonance effect has been achieved from the Raman peak shift, lineshape, and intensity through changing the Mg composition and temperature to tune the ZnMgO bandgap. By the aid of theoretical analysis combining with the extrinsic Fröhlich interaction mediated via a localized exciton, we demonstrate the pronounced outgoing resonance behavior for the LO phonons in ZnMgO, where the localized exciton due to alloy disorder dominates the resonance processes.

Interfacial and bulk polaron masses in Zn1−xMgxO/ZnO heterostructures examined by terahertz time-domain cyclotron spectroscopy

“…1(b). This phonon blueshifts with increasing x, in agreement with previous studies, 14,15 Terahertz time-domain spectroscopy 17,18 was utilized to determine the complex magnetoconductivity in the frequency range 100 GHz < ω/2π <2 THz. Samples were placed in the variable-temperature insert of a split-coil superconducting magnet, which applied a magnetic field B along the c-axis.…”

Structural and optical analysis of ZnBeMgO powder and thin films

“…Moreover, there exists a miscibility gap in the ZnO-MgO binary system due to the structural difference and the large lattice mismatch between ZnO (hexagonal wurtzite, 3.25Å) and MgO (cubic rock salt, 4.22Å) [12]. Mg 2+ ions (0.57Å) can replace 33 at.% of Zn 2+ ions without changing the structure of ZnO whereas phase segregation between hexagonal ZnO and cubic MgO was observed in Zn 1−x Mg x O alloy with more than 36 at.% Mg-content [12,[15][16][17]. Therefore, the attention shifted towards another binary system ZnBeO [23,24].…”

“…During this decade, the band gap modulation of ZnO films has been achieved by alloying it with much wider band gap semiconductor MgO (7.8 eV) [12][13][14][15][16][17][18][19][20]. Our group reported the fabrication of stable wideband gap (∼6 eV) ZnO/MgO multilayer thin films using pulsed laser deposition (PLD) technique on c-axis oriented sapphire substrate [21].…”

Photoluminescence and Raman spectroscopy characterization of highly c-axis oriented MgxZn1−xO thin films on Pt-coated silicon substrates

“…The calculated c-axis lattice constants of hexagonal structure decrease linearly from 0.5208 nm to 0.5191 nm with Mg contents from 0 to 0.2. Therefore, the shortening c-axis lattice and broadening (002) FWHM indicate successful incorporation of Mg into ZnO lattice due to the different radii of Zn 2+ ion (0.6Å) and Mg 2+ ion (0.57Å) [3,9,10]. It is worth noting that the extent to decrease of c-axis lattice due to Mg incorporation is smaller than previous reports [3,4].…”

“…It is reasonable that excessive Mg incorporation into ZnO can cause the increase of nonradiative recombination lifetime and recreate the structure-related defects like disorders and boundaries, deteriorating the films quality. Theses factors can result in the intensifying deep level luminescence and depression of the photoluminescence of NBE peaks [9,11]. Figure 4 shows Raman spectra (200~900 cm −1 ) of the Mg x Zn 1Àx O x ¼ 0 $ 0:2 ð Þthin films deposited on Pt/TiO 2 / SiO 2 /Si substrates, from which the effect of Mg doping levels on vibrational properties of ZnO lattice has been investigated.…”