[Effects of Ag nanocrystals on electroluminescence in Si oxide films].

Ag nanocrystal-embedded silicon oxide (SiO2 : Ag) films with varying Ag fractions were prepared on p-Si substrate by magnetron co-sputtering and thermal annealing. Visible electroluminescence (EL) was observed from the structures of ITO/SiO2 : Ag/p-Si. The authors found that Ag nanocrystals in the SiO2 film can not only shift the EL peak evidently but also enhance the EL intensity markedly. The larger the Ag fractions in the EL structures, the longer the peak wavelengths. The electromagnetic interactions of the Ag nanocrystals with the emitters in the film via local surface plasmons are considered responsible for these experimental results.

[Electroluminescence from a Mn2+ activated SiO2 : Si film on N(+)-Si substrate].

Recently, a monolithic integration of optics and electronics in a single Si chip has attracted a great deal of attention due to its attractive application prospects: the potential for forming high speeded information processing and transmission, and inexpensive and low power silicon chip. Developing high-efficiency silicon-based light sources is the main task in silicon photonics. In the present paper the authors explore a potential way for silicon-based light-emitting application. A Mn(2+)-activated silicon-rich silicon oxide (SiO2 : Si : Mn2+) film was prepared on the n(+)-type silicon substrate using co-sputtering technique followed by doping and activation of Mn with a thermal diffusion method. High-resolution transmission electronic microscope study shows that the film is embedded with 3-5 nm silicon nanocrystals. Bright green photoluminescence (PL) from the film was observed under ultraviolet radiation and peaked at 524 nm (2.36 eV), the decay time of which is 0.8 ms. It is generally believed that the green radiation originates from 4T1 --> 6A1 transition in Mn2+. The PL excitation spectrum of the film, monitored at 524 nm, has a peak of 254 nm, similar to that of the Zn2 SiO4 : Mn film. It is believed that the strong 254 nm absorption is attributed to Mn2+ --> Mn3+ ionization or ds --> d4s transition. A very broad electroluminescence spectrum ranging from 400 to 800 nm, covering almost the whole visible band, was observed from the device made of the SiO2 : Si : Mn2+ film at low reverse biases. The threshold voltage of the device is as low as 5 V. Spectra of the device demonstrate that the electroluminescence is attributed to Mn2+ and luminescence centers in the Si-rich SiO2 film. The authors interpret that Mn2+ excitation is mainly due to direct impact excitation of hot electrons, silicon nanocrystals in the SiO2 film help electrons tunnel from a silicon nanocrystal to an adjacent one, and are advantageous for generating hot electrons to excite Mn2+.