| The Ill-nitrides AlN, GaN and InN with related alloys form an interesting class of wide bandgap materials, which are likely to be the basis of a strong development of a novel family of semiconductor device, for Optronics as well as for electronics. For example, the entire spectral region from UV to red can be covered with III-N optical devices. Furthermore, AlN has some outstanding physical properties that have attracted much interest. Its hardness, high thermal conductivity, resistance to high temperture and caustic chemicals, makes AlN an attractive material for electronic and optical devices. However, the majority of interest in AlN stems from the properties of its alloys with GaN which may permit the fabrication of AlGaN based optical devices which are active from the blue wavelength well into the UV.In this study, AlN thin films have been deposited on n-Si (100) and quartz substrates by reactive radio frequency magnetron sputtering. And the influence of substrate temperture and sputtering pressure is emphasized. The morphological and structural chacterizations have been determined by Rutherford backscattering spectroscopy, atomic force microsiscopy, transmission electron microscopy, x-ray diffraction, reflection high energy electron diffraction, Fourier transform infrared spectroscopy and ellipsomerty. Optical constants and thickness have been analyzed from the transmittance and scanning electron microscopy. In the mean time, the relationships between intensity of line spectrum of aluminium, nitrogen, argon, oxygen and sputtering parameter were discussed from emission spectrum of the plasma ambience.The major points of this work were summarized as folio wings:I Morphological and structural characterization of nano-scale AlN thin films deposited at different substrate tempertureA. AlN thin films in nano-scale deposited at high sputtering pressure (2.5Pa) are with atomistic smoothness. And the surface roughness with a root mean square(rms) roughness ~0.4nm has little changes with the substrate temperture varied from room temperature to 550C. But AlN thin film growth behavior varies with substrate temperture and could be classified into three types which are the growth with non-diffusion at room temperture, the growth with finite diffusion at 150C-450C, the growth with diffusion at 550C.B. The grAlN size of the film deposited at 550C is in the range of 20 nm to 30 nm, while thegrAlN size of the film deposited at room temperature is about 10 nm. And the rising of refractive index of AlN thin film with increasing substrate temperture shows that the crystallization of AlN thin films are improved.II Morphological and structural characterization of AlN films deposited at various sputteringpressureA. At a certAlN substrate temperature, the decreasing sputtering pressure from 1.2Pa to 0.3Pa makes the size of surface island largened obviously. Furthermore, the preferred orientation of the AlN film changes from polycrystalline structure to c-axis oriented as the sputtering presure decreasing.B. The growing process of AlN film could be divided into three stages which are the amorphous region, the region of nucleation and competition in the growth, the growth of crystalline AlN. Moreover, the amorphous layer of 5 nm thickness in the initial stage provides nucleation sites for the groeth of c-axis oriented crystallites.IllOptical and structural characterization of AlN films deposited at various sputtering pressureA. The ranges of the optical constants calculated from the transmittance in the spectral range of 190-1100 nm are as follows: thickness d =388-1158nm, refractive index n633=1-8915 -2.0346, n350=1-9854-2.1284, extinction coefficient k633=0.2625x10-3-2.2700x10-3, k350 =2.2500x10-3-4.8700x10-3. The optical band gaps ranges between 5.590 and 6.109 eV.B. The crystal structure and crystalline orientation of AlN films on quartz substrate were measured by x-ray diffraction. It is found that structural characterization of AlN films are similar deposited on whether n-Si (100) or quartz substrate. |
PDF Full Text Request