Photoluminescence Spectra Of ZnO Films Research Articles

Persistent photoconductivity in ZnO thin films grown on Si substrate by spin coating method

Photoluminescence (PL) and photoconductivity (PC) have been studied in ZnO thin films grown on Si substrates by a spin-coating method. The PL spectra of ZnO films, studied under synchrotron radiation excitation in ZnO fundamental absorption range at 10 K, show the dominant UV emission band with two maxima at 3.28 and 3.235 eV corresponding to the luminescence of localized excitons around neutral and charged donors and acceptors, respectively. The PC measurements of ZnO films were performed in the air and in a vacuum. The UV irradiation of ZnO films results in the appearance of induced photocurrent. The dependence of photocurrent value in air/vacuum atmosphere on the intensity of UV radiation was investigated.

Intensity of visible and IR emission of intracenter 4f transitions of RE ions in Er- and Tm-doped ZnO films with additional Ag, Li, and N impurities

The use of Ag impurity in Er-doped ZnO films deposited by AC magnetron sputtering with a low growth rate has increased the emission intensity at λ = 1535–1540 nm. An increase in the deposition rate and in the temperature of substrates, as well as the use of Li and N+ impurities, led to a considerable increase in the intensity of the line with λ = 376–379 nm in the case of doping with rare-earth ions (Er, Tm), which makes it possible to use this semiconductor for creation of devices for the short-wavelength spectral region. Introduction of additional impurities in Er-doped ZnO films deposited on bulk ZnO crystals with increasing deposition rate and temperature caused an increase in the intensity of the line with λ = 1535–1540 nm. The photoluminescence spectra of ZnO films doped with Tm (ZnO ) exhibited intense emission of lines with λmax = 377 nm.

Hydrothermal synthesis of 2D ordered macroporous ZnO films

The ZnO films with two-dimensional ordered macroporous structure were successfully fabricated through hydrothermal crystal growth of ZnO on the ZnO substrate covered with a monolayer of polystyrene (PS) spheres as template. The precursor solution of hydrothermal crystal growth of ZnO were prepared by equimolar solution of Zn(NO3)2·6H2O and hexamethylenetramine (HMT). The confinement effect of the PS spheres template on the growth of ZnO nanorods and the influence of sodium citrate on the crystal growth of ZnO had been studied. The film surface morphology and the preferential growth of ZnO crystal were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Also, the photoluminescence spectrum of ZnO films had been measured, and the corresponding mechanism was discussed.

NH3-assisted growth approach for ZnO films by atmospheric pressure metal-organic chemical vapor deposition

In this paper, we investigated the two effects of a little H2 and NH3 gas on the properties of ZnO films grown by atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD) using deionized water (H2O) and diethylzinc (DEZn) as the O and Zn sources, respectively. Experimental results showed that compared to the effect of a little H2, it could more effectively improve the surface morphology, crystalline structure, and optical quality of ZnO epilayers by adding a little NH3 gas into the growth ambient. Furthermore, by adding a little NH3 gas into the growth ambient, the hydrogen-related D0X1 (I4):3.365 eV peak disappeared in 10 K photoluminescence spectrum of ZnO films, which indicated the elimination of the unintended hydrogen impurity. The result of the Huang–Rhys factor S (0.113) showed that it was effective for reducing the probability of exciton–phonon scattering of ZnO films by adding a little NH3 gas into the growth ambient. The electron mobility of ZnO films were also significantly improved by this method with the mobility of 100 cm2V-1s-1 measured by Hall measurement at room temperature.

Homoepitaxial growth of non-polar ZnO [formula omitted] films on off-angle ZnO substrates by MOCVD

Homoepitaxial ZnO ( 1 1 2 ¯ 0 ) films were successfully prepared on single crystal ZnO ( 1 1 2 ¯ 0 ) substrates with off-angles of 0°, 1°, 2° and 3° toward the [ 1 1 ¯ 0 0 ] direction by using an atmospheric pressure MOCVD. A striped pattern along the ZnO [0 0 0 1] direction was observed in ZnO films, and surface smoothness of ZnO films was remarkably improved by increase in off-angle. Full-width at half-maximum of XRD patterns of rocking curves and 2 θ– ω scans for (0 0 0 2) and ( 1 0 1 ¯ 0 ) planes measured by grazing incident diffraction measurement was decreased with increase in off-angles. Free exciton emissions and donor-bound exciton emissions were clearly observed in the photoluminescence (PL) spectra of ZnO films deposited on ZnO substrates with off-angles measured at 5 K. Room temperature PL spectra of ZnO films have a strong band edge emission on the samples with ZnO films deposited on off-angle substrates.

Structure and UV emission of nanocrystal ZnO films by thermal oxidation of ZnS films

ZnO films prepared by the thermal oxidation of the ZnS films through thermal evaporation are reported. The as-deposited ZnS films have transformed to ZnO films completely at 400 °C. The 400–700 °C annealed films with a preferential c-axis (0 0 2) orientation have a hexagonal wurtzite structure. The band gap of ZnO films shifts towards longer wavelength with the increase of the annealing temperature. The relationship between the band gap energy of ZnO films and the grain size is discussed. The shift of the band gap energy can be ascribed to the quantum confinement effect in nanocrystal ZnO films. The photoluminescence spectra of ZnO films show a dominant ultraviolet emission and no deep level or trap state defect emission in the green region. It confirms the absence of interstitial zinc or oxygen vacancies in ZnO films. These results indicate that ZnO film prepared by this simple thermal oxidation method is a promising candidate for optoelectronic devices and UV laser.

Effect of ultrasonic treatment on ZnO film photoluminescence

The photoluminescence spectrum of ZnO film with high crystal quality has been measured. The peak of near-ultraviolet emission located at 389 nm has been observed. For the ZnO film treated by ultrasonic, not only the ultraviolet peak of ZnO, but also the strong green peak at 508 nm have been observed. It is also found that the intensity of the green peak (508 nm) is stronger than that of the ultraviolet peak. The ultraviolet peak also appears to have red-shift. The intensity of the green peak (508 nm) increases sharply with further heating. The crystal quality of ZnO films is changed by the ultrasonic treatment and oxygen vacancies are produced. The lattice vibration of film is aggravated in the treatment process. When the lattice vibration arrives at certain degree, the lattice oxygen leaves the lattice site to form oxygen vacancy, and the green peak (about 510 nm) is attributed to oxygen vacancies in the crystal. The density of oxygen vacancies depends on the ZnO film temperature. The higher the film temperaure, the greater the density of oxygen vacancy and the stronger the intensity of the green peak.

Photoluminescence Spectra of ZnO Films Doped with Li and Cl Atoms

ZnO films doped with Li and Cl atoms have been prepared by organometallic chemical vapor deposition method. In photoluminescence spectra of the doped ZnO films, strong emission appears at 376 nm which is slightly longer than that of free-excitons. As excitation intensity increases, a peak wavelength of the emission is shifted toward a shorter value. The emission near band-gap edge is assigned to radiative recombination via Li-Cl pairs.