Growth and Characterization of ZnO Film on Sapphire by the Helicon Wave Plasma Assisted Evaporation Process

The growth of ZnO film on (0001) sapphire substrates was studied using the high density helicon wave oxygen plasma (>1011/cm2) assisted evaporation process. The addition of Ar into oxygen plasma (Ar/O2=1/2) enhanced the production of excited atomic oxygen (O*). The effect of a grounded grid installed at the exit of the plasma source on the crystallinity and optical properties of film is discussed. The full width at half maximum (FWHM) of θ rocking curve for (0002) plane is 0.53° under grid installation while 0.63° without the grid, indicating slightly improved crystallinity when adopting a grounded grid. The AFM image for the film deposited with grid installation shows a smoother surface morphology than in the case of no grid. PL spectra for the film deposited with the aid of a grid show a strong near-band edge emission at 3.36 eV at 10K, but those without a grid show prominent deep-level emissions. The deep level emission is attributed to the impurities and native defects in the film. The optical properties were greatly improved by a grounded grid, which effectively eliminated the ionic species and selectively extracted the excited neutrals.