Abstract
In this thesis, we present the results of a detailed examination of the possible origins of the luminescent silicon nitride and oxynitride thin films. The luminescent silicon-rich oxynitride and nitride thin films are successfully deposited on single crystalline silicon wafer substrates at 300℃ by using the electron-cyclotron-resonance chemical-vapor-deposition (ECR-CVD) technique with SiH4-Ar-N2 or N2O mixture gases. The photoluminescence peak energy emitted from these samples can be tuned from the blue to the near-infrared by adjusting the degree of silicon richness. It was found that the luminescence yield of our thin films is comparable to the bulk GaAs sample at room temperature without post-annealing. The PL degradation time constant at the maximum PL energy of the samples was found to be in the second range. The PL intensity and degradation time decreases with increasing the silicon content. Spontaneous emissions from these thin films were found to be spectrally coupled to the longitudinal modes of a vertical cavity with film/substrate and air/film interface mirrors. These observations demonstrate the possibility to enhance and control the spontaneous emission through the use of microcavity. The EXAFS and XANES measurements demonstrated the formation of the silicon clusters in the silicon-rich nitride and oxynitride films. It is noted that no obvious bond length variation could be found in the samples with different degree silicon richness. From the high-resolution cross-sectional transmission-electron-microscopy images, some small (<3nm) regions can be seen which are slightly darker, however, does not show lattice fringes. The images in the flimsy edge of samples exhibit clear lattice fringes and the clusters with size about 1-3 nm can be clearly identified. These observations demonstrate the existence of the nano-crystalline silicon clusters in the luminescent silicon-rich samples. Using two-color resonent photoemission, we successfully detect the unoccupied localized gap state which is located above the valence band maximum at about 2.4-1.8 eV, changed with the silicon content. Moreover, the resonance photoemission results indicated that the top valence band is dominated by the oxygen-related and/or nitrogen-related bonding. The PLY near-edge feature shows that the co-existence of Si-Si and Si-N luminescence sites. This observation combined with microstructure characterization strongly suggests that silicon cluster embedded in the silicon nitride or silicon oxynitride matrices model seems to provide the only viable explanation on the origin of photoluminescence. In conclusion, adjustable intense photoluminescence at room temperature was observed from the hydrogenated amorphous silicon-rich nitride and oxynitride thin films in the range from blue to near-infrared. The electron-hole recombination in samples via carriers trapped in nitroge/oxygen-related localized states that are stabilized by the widening of the gap induced by quantum confinement. This phenomenon is an inevitable result of silicon clusters embedded in the amorphous oxide/nitride environments.