C.Z. Tan

Enhanced ultraviolet photoluminescence from SiO2/Ge:SiO2/SiO2 sandwiched structure

SiO2/Ge:SiO2/SiO2 sandwiched structure was fabricated for exploring efficient light emission. After annealed in N2 (O2<1%), this structure shows three photoluminescence (PL) bands at 293, 395, and 780 nm. The intensity of the 395 nm band is largely enhanced in comparison with that from the monolayered Ge:SiO2 film. Spectral analyses suggest that the three PL bands originate from S1→S0, T∑(T∏)→S0, and T∏′→S0 optical transitions in GeO color centers, respectively. The improvement of the GeO density resulting from the confinement on Ge diffusion is responsible for the enhanced ultraviolet PL. This structure is expected to have important applications in optoelectronics.

Blue emission from silicon-based β-SiC films

Abstract β -SiC films were fabricated on 〈100〉- and 〈111〉-oriented silicon substrates by pulsed laser deposition. The photoluminescence (PL) spectrum shows two blue emissions at 416 and 435xa0nm. Their positions do not change with both the substrate orientation and β -SiC crystallite sizes. High-resolution transmission electron microscopy observations display that the fabricated films contain both β -SiC and Si nanocrystallites. Fourier-transform infrared absorption and electron paramagnetic resonance measurements provide the evidences that the radiative recombination of carriers responsible for the two blue emissions takes place in a kind of silicon excess defect centers (D centers, ·Siue5fcSi 3 ) at the surfaces of β -SiC crystallites, whereas the photogeneration of carriers partially occurs in the β -SiC crystallite cores. The obtained results are expected to have important applications in modern optoelectronic devices.

Correlation of electroluminescence with Ge nanocrystal sizes in Ge-SiO2 co-sputtered films

Abstract Ge-doped SiO 2 films were deposited on p -Si substrates by magnetron sputtering and metal–insulator–semiconductor (MIS) structures were fabricated with semitransparent Au layers on SiO 2 films. The MIS structures exhibit electroluminescence (EL) peaked at 590 nm. The positions of the EL peaks from the samples with different Ge nanocrystal sizes keep unchanged. The maximal peak intensity appears in the sample annealed at 600°C in N 2 atmosphere, in which the average size of Ge nanocrystals is about 4 nm. X-ray diffraction results show that the EL intensities are closely related to Ge nanocrystal sizes. Theoretical analyses suggest that the energy gaps of Ge nanocrystals relate with the discrepancy of EL intensities by influencing transport properties of carriers. Our experiments provide a possible avenue for improving the EL intensity, which will be more useful in optoelectronics.

Strong violet emission from Ge–SiO2 co-sputtered films annealed in O2 atmosphere

Abstract Photoluminescence (PL) spectra of Ge–SiO 2 co-sputtered films annealed under O 2 , N 2 , and air were examined using the 250 nm excitation line of Xe lamp. Violet and ultraviolet PL peaks were observed at ∼400 and ∼300 nm. The two peaks were found to have a similar behavior with annealing temperature. Their maximal intensities appear in the sample annealed at 800°C and in O 2 atmosphere. Fourier transform infrared absorption results suggest that the two PL peaks are closely related to Ge oxide in the samples. The PL excitation spectral examinations indicate that they arise from optical transitions in GeO color centers. The existence of oxygen during annealing improves the GeO density in the samples and makes the PL intensities enhanced largely. Our experiments provide a way for improving the violet and ultraviolet PL intensities, which will be more useful in device applications.