Search

High orientated undoped ZnO thin films were prepared on c-Al2O3 substrates by pulsed laser deposition(PLD) method and using ZnO ceramic target as resource material.The photoluminescence(PL) origin of the ZnO thin films was discussed in detailed.PL spectrum of ZnO thin films is dominated by donor-bound exciton(D0X)emission at low temperatures while the free exciton transition(FX) gradually dominates the spectrum at higher temperatures.It notes that one emission band A at around 3.309 eV(T=10 K) can be clearly observed with increase in temperature up to room temperature.The mechanism of this emission band was investigated by the temperature dependence of PL spectra.The results can be attributed to the transition of conduction band electrons to acceptors(e,A0),in which the acceptor binding energy was approximately 129 meV.However,the formation mechanism of the acceptor states need be investigated further.

Gadoped ZnO(GZO) thin films were grown on single crystal silicon(111) and quartz glass substrates by pulsed laser deposition(PLD) method at different substrate temperatures from room temperature to 750 ℃.The change of substrate temperature leads to different diffusion and desorption rates for adsorption atoms resting on substrate surface,and results in different crystalline quality for GZO thin films.The GZO thin film grown at 450 ℃ has the best crystalline quality.The carrier concentration monotonically decreases with the increase of substrate temperature,which is related to the intrinsic defects in films.The Hall mobility first increases and then decreases with the substrate temperature increasing,it results from the variation of grain boundary scattering.And the lowest resistivity ~0.02 Ω·cm is obtained in the film prepared at 450 ℃.With the increase of substrate temperature,the optical band gap becomes narrow due to the monotonic increase of carrier concentration.The average transmittance in visible region is above 85% for all the GZO samples.Our results exhibit that the optical and electrical properties of GZO thin films prepared by PLD method can be adjusted by the change of substrate temperature.

H∶ZCO thin films were prepared with different qv(H2)∶qv(Ar+H2) by using submolecule doping technique,where the magnetic sputtering of Co and ZnO were alternatively performed onto silicon substrates.The effect of qv(H2)∶qv(Ar+H2) on the structural and magnetic properties in films was investigated.All the prepared thin films have a c-axis preferential orientation,and the intensity of(002) diffraction peak decreases with the increase of qv(H2)∶qv(Ar+H2) in films because the doping hydrogen can passivate the dangling bonds at the surfaces and grain boundaries.Magnetic measurement shows that the ferromagnetism is enhanced with the qv(H2)∶qv(Ar+H2) increasing.XPS results exhibit that the relative content of Co metal clusters gradually increases,and the relative content of oxidized Co ions gradually decreases with the increase of H2 ratio.According to the above results,it is suggested that the ferromagnetism in H∶ZCO thin film originates from Co metal clusters,and more oxidized Co ions is reduced to Co metal clusters with H2 doping,therefore the ferromagnetism is enhanced.

HAZO films were prepared on quartz substrates by RF magnetron sputtering in Ar+H2 gas ambient at room temperature.The effects of post-annealing in pure Ar atmosphere on the structural,optical and electrical properties of the HAZO films were investigated.It was found that post-annealing treatment was beneficial to crystallization of HAZO thin films,while caused a large degradation of the conductivity.The increase in the resistivity of HAZO thin films was attributed to the doped hydrogen atoms diffuse out after annealing.It was showed that interstitial hydrogen atoms(Hi) and substitutional hydrogen atoms(HO) at an O site removed from films,as well as the effect of H passivating deep acceptors and dangling bonds gradually eliminated as the heating temperature was increased.

The ZnO films grown with different growth temperature have been deposited on c-Al2O3 substrates by plasma assistant molecular beam epitaxy(P-MBE).Their crystal structures are characterized by X-ray diffraction(XRD).The XRD results indicate that all the ZnO films with the(002) preference orientation of hexagonal wurtzite structure.The full width at half maximum(FWHM) of the(002) diffraction peak decreases as the growth temperature increasing.The surface morphology of the ZnO films is measured by scanning electron microscope(SEM),the surface morphology of the ZnO films grown at different growth temperature changes gradually.In the SEM image of the film grown at 500 ℃,there are a large number of particles,and the surface of the film is rough.The particle size is about 50~100 nm.The particle size increases(about 100~200 nm) at 600 ℃ growth,which indicates that the particle size increase with the increasing of the growth temperature.As the film growth temperature reaches 700 and 800 ℃,it can be found that the surface of the film become uniform and smooth from the SEM image.The photoluminescence(PL) intensity of the ZnO film increased with the increasing of the growth temperature.The origin of the PL peak is the free exciton emission.The carrier concentration and Hall mobility of the films as a function of growth temperature are studied.Hall measurements show that all the films are n-type.The carrier concentration value decreases gradually from 3.4×1018 cm-3 to a value of 1.8×1018 cm-3 with increasing the growth temperature from 500 to 800 ℃.The Hall mobility of ZnO films rises from 11 cm2/(V·s) to 51 cm2/(V·s) with the increase of film growth temperature.The high quality ZnO thin films was obtained at 800 ℃,exhibiting that the FWHM of XRD is about 0.05°,the Hall mobility is about 51 cm2/(V·s),the carrier concentration is about 1.8×1018 cm-3.