Preparation And Characterization Of Silicon-based Nanocrystalline Arrays

Nanocrystalline (nc-Si) Si-based materials have attracted broad attentions due to their potential application in the future integrated optoelectronics and nanodevices. From the viewpoint of device application, a challenge we face is that how can we precisely control the size and distribution of nc-Si using the technology in existence.In this thesis, anodic aluminium oxide (AAO) was used as a patterned substrate to prepare well-aligned Si-based nanodot arrays by plasma enhanced chemical vapor deposition. The structure, morphology, electrical and optic properties of the arrays were characterized. The main results we obtained are as following.First, the properties of AAO templates dependent on oxidization voltage, temperature and time were investigated. High quality AAO templates with preconceive parameters, such as the size and distribution of the nano holes were prepared using two-step oxidization.Secondly, Si films with nanodot arrays were prepared on AAO templates by plasma enhanced chemical vapor deposition (PECVD). By optimizing the deposition conditions, such as reaction pressure and growth time, we obtained well-aligned amorphous Si (a-Si:H) nanodots. Then the samples were annealing at a temperature of 550 ℃ for 5 hours in N₂ atmosphere to crystallize the resultant a-Si:H.Thirdly, the structure and morphology of Si nanodot arrays were evaluated by X-ray diffraction spectroscopy (XRD), Fourier transition infrared spectrum (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD and FTIR results indicated that the structure of the as-deposited samples on AAO templates was amorphous and H atoms were incorporated in the Si network in a configuration of SiH₂ After annealing, the H atoms were removed and the samples were crystalline. The SEM and TEM images showed that Si films were formed with excellent nanodot arrays duplicating the morphology of the used AAO templates. The growth mechanism Si nanodot arrays was described.Then, photoluminescence spectra of Si nanodot arrays showed a strong visible light emission at room temperature. It suggest that every Si dot possesses of umptymicrocrystalline grains. The dot with bigger diameter consists of grains with larger size. The study of field emission character on the samples showed a good behaviour of electron field emission. No initial activation process was found for the emission, which suggested a kind of non-destructive mechanics of electron field emission. The typical threshold voltage for emission is 7 V/um. In-suit conductance measurements were performed during decreasing the temperature.Finally, a series of nc-Sii.xGex nanodot arrays were obtained by PECVD method on AAO templates. The structure of the samples was evaluated by TEM, XRD,EDS and FTIR measurements. The XRD and Raman spectra indicated that the samples were crystallined by annealing, and the strains were not relaxed. PL spectra showed a remarkable red shift with increasing the content of Ge. The dependence of conductivity on temperature was studied and it was found that with the increase of strains, the electron tunnelling was enhanced at the temperature below 171 K.