As a wide-gap Ⅱ Ⅵ oxide semiconductor

ZnO is known to have a band gap of about 3.3eV and large binding energy of excitons (59meV) at room temperature. Recently

ZnO-based semiconductors and related heterostructures are attracting more interest because of their promising optoelectronic applications in the ultraviolet wavelength range. To obtain the high performance light emitting devices

the key technique is to construct a heterojunction to realize double confinement action to electrons and photons in optoelectronic devices. Mg

x

Zn

1-x

O alloy thin films have been studied extensively as their potential barrier materials. Mg

x

Zn

1-x

O alloy thin films were fabricated on c plane sapphire (Al

2

O

3

) substrates by plasma assisted molecular beam epitaxy (P MBE). The films with different composition x

which is changed from 0 to 0.20

kept wurtzite crystal structure measured by X ray diffraction (XRD). X ray double crystal diffraction spectra show that the samples are single crystal films. As x value was increased from 0 to 0.20

the full width at half maximum (FWHM) of (002) oriented ZnO X ray rocking curve is broadened from 0.25° to 0.71° and the lattice constant of c axis is decreases from 0.5205nm to 0.5185nm. Photoluminescence (PL) spectra at room temperature(RT)exhibit an intense ultraviolet emission

without the deep level emission. With increasing x values

FWHMs of the emission peak change from 62meV to 89meV and peak positions shift to high energy side from 3288eV to 3467eV. The absorption edges of alloy thin films show the blue shifts with increasing x value in the transmission spectra at RT. The origin of the ultraviolet emission is studied by the measurements of the PL spectra at different temperature. The result shows that this emission comes from the recombination of neutral and ionized donor-excitons. Two steps dissociation process of neutral donor-exciton complexes is found

in which the thermal quenching mechanism is attributed to the dissociation of a free electron from the complex and the dissociation of two free electron and a free hole from the complex.