xMgxO Alloy Research Articles

Strong excitonic transition of Zn1−xMgxO alloy

A strong excitonic optical transition in a Zn1−xMgxO alloy grown by radical source molecular beam epitaxy was observed using both optical reflectivity measurements and photoluminescence (PL) measurements. Clear and strong reflectance peaks at room temperature (RT) were observed from 3.42eV (x=0.05)to4.62eV (x=0.61) from ZnMgO layers at RT. Distinct clear PL spectra at RT were also observed for energies up to 4.06eV (x=0.44). The peak intensity of the reflected signal increased for x values up to x∼0.2 simultaneously with an increase in PL intensity; however, a Stokes shift between the reflectance peak and the PL peak was not observed for x values below 0.2. These facts suggest that the oscillator strength of ZnMgO is enhanced by alloying, and the underlying mechanism is discussed. Furthermore, we demonstrate that the strong reflectance properties even at RT provide an easy method to determine the Mg composition of a thin ZnMgO layer in a ZnMgO∕ZnO heterostructure.

Photoluminescence characterization of Zn1−xMgxO epitaxial thin films grown on ZnO by radical source molecular beam epitaxy

The authors report that high-quality Zn1−xMgxO alloys are very brilliant light emitters, even more brilliant than ZnO, particularly in the high-temperature region; both the emission bandwidth and the oscillator strength of the photoluminescence from Zn1−xMgxO alloys increase remarkably with increasing Mg composition ratio x. The authors have revealed that the increase in the oscillator strength is mainly due to the increase in the activation energy required for the nonradiative recombination processes. Therefore, it is suggested that the localization of excitons, because of the compositional fluctuation, takes place in Zn1−xMgxO alloys and that the degree of the localization increases with increasing x.

Structural and optical properties of single crystal Zn1−xMgxO nanorods—Experimental and theoretical studies

Structural and optical properties of single crystal Zn1−xMgxO nanorods (0≤x≤0.17) are studied experimentally and theoretically. Structural analyses indicate that the nanorods grown on Si substrates are oriented in the c-axis direction and the nanorods possess the single-crystalline hexagonal structure with the Mg incorporated within the ZnO nanorods by means of substituting Zn. A blueshift of the near-band edge emission in the photoluminescence spectra by increasing Mg content is observed. Two distinct emission bands are found in the photoluminescence spectra; one is mainly attributed to the delocalized exciton recombination and the other is originating from localized excitons due to the incorporation of foreign impurity of Mg. Enhanced exciton localization with increasing Mg content in Zn1−xMgxO nanorods is mainly due to large ionic characters of Mg-O bonding. Structural stability, band structures, projected density of states, and charge distribution in various Zn1−xMgxO alloy compounds were further investigated by first-principles calculations. A good agreement between experimental and theoretical results is found.

Carrier concentration induced band-gap shift in Al-doped Zn1−xMgxO thin films

Transparent conducting Al-doped Zn1−xMgxO thin films were grown on glass substrates by chemical vapor deposition. The resistivity could be lowered to 10−3Ωcm with optical transmittance above 85% in visible regions. The influence of carrier concentration on band-gap shift in Zn1−xMgxO alloys was systematically studied. The shift of energy gap could be fully explained by the Fermi-level band filling and band-gap renormalization effects. As the Mg content increased, the electron effective masses in Zn1−xMgxO (x=0–0.21) alloys increased from 0.30m0 to 0.49m0. The Al-doping efficiency was reduced with the increase in alloy composition.

Structural and optical properties of Zn1−xMgxO nanocrystals obtained by low temperature method

In this paper we report structural and optical properties of magnesium substituted zinc oxide (Zn1−xMgxO) nanocrystals (∼10–12nm) synthesized by low temperature route. In the low temperature synthesis route it was possible to reach x=0.17 without segregation of Mg rich phase. The exact chemical composition has been established by quantitative analysis. Rietveld analysis of the x-ray diffraction (XRD) data confirms the wurtzite structure and a continuous compaction of the lattice (in particular, the c-axis parameter) as x increases. There is an enhancement of the strain in the lattice as the Mg is substituted. The band gap also gets enhanced as x is increased and reaches a value of 4eV for x=0.17. From the transmission electron microscope and the XRD data it has been concluded that when there is a phase segregation for x>0.17, there is a shell of Mg(OH)2 on the ZnO. The absorption also shows persistence of the excitonic absorption on Mg substitution. The nanocrystals show near band edge photoluminescence (PL) at room temperature which shows blueshift on Mg incorporation. In addition to the near band edge emission the ZnO and Zn1−xMgxO alloy nanocrystals show considerable emission in the blue-green region at wavelength of ∼550nm. We find that the relative intensity of the green emission increases with the Mg concentration for very low x (up to x=0.05) and on further increase of the Mg concentration there is a sharp decrease of relative intensity of the green emission eventually leading to a complete quenching of green emission. It is concluded that due to phase segregation (for x⩾0.20), the formation of the shell of Mg(OH)2 on the ZnO leads to quenching of the green emission. However, this shell formation does not have much effect on the near band edge PL.