Nanostructural and Optical Features of nc-Si:H Films Prepared by Aluminium-induced Crystallization

초록

Hydrogenated nanocrystalline silicon (nc-Si:H) has attracted much attention in electronic industry for its potential applications in photoluminescence (PL) and electroluminescence (EL) devices based on Si. Silicon is an indirect band structured material with a band gap of ~ 1.1 eV. Therefore, it cannot emit visible light at R.T. and as a result Si-based technologies can’t be applied in optoelectronics. However, PL phenomena have recently been observed from nc-Si films if Si nanocrystallites with the size of less than 5 nm exist in the films. The luminescence is extremely sensitive to the size and fraction of the nanocrystallites. Since the size distribution of silicon nanocrystallites in the films is generally broad, the PL spectrum is also broad and featureless. Recently, the aluminium-induced crystallization (AIC) technique has been reported to lead to the formation of grains in Si films on foreign substrates. It is explained by the overall layer exchange of Si with Al films or vice versa during the transformation of amorphous (a-Si) to crystalline Si. The Al migrates from interface into Si layers, dissociating a large amount of Si material. The dissociated Si readily diffuses to the Al layer, creating Si nuclei and growing crystalline Si grains. In this study, we investigated the effect of Al-doping on the nanostuctural features of nc-Si:H thin films by thin film XRD, HRTEM, Raman S., and PL. Nc-Si:H thin films were prepared by plasma enhanced chemical vapor deposition (PECVD) techniques. Raman spectra (JOBIN YVON T64000) were recorded using a single monochromator with 514.53 nm excitation line of an Ar-ion laser in a wavenumber region of 200 ~ 800 cm-1. PL measurement (SPEX, 1403) was carried out at R.T. with 55 mW, He-Cd laser excitation at 325 nm. The nanostructural, chemical, and optical features of nc-Si thin films were investigated as a function of the amount of doped-Al and heat-treatment conditions.