Peigao Han

Strong green-yellow electroluminescence from oxidized amorphous silicon nitride light-emitting devices

High efficiency luminescent amorphous silicon nitride films grown at room temperature with subsequent plasma oxidation were used as the active layers in the electroluminescent devices. A strong uniform green-yellow light emission from the devices was realized under forward biased conditions. It was found that the turn-on voltage could be reduced to as low as 6V while the electroluminescence (EL) intensity is significantly enhanced by two to four times by using p-type Si anode instead of indium tin oxide substrate under the same forward voltage. Furthermore, the EL peak position is blueshifted from 560to540nm, which is more close to that of the corresponding photoluminescence peak. The origin of light emission is suggested to be the same kind of luminescent centers related to the Si–O bonds.

Intermediate phase silicon structure induced enhancement of photoluminescence from thermal annealed a-Si/SiO2 multilayers

a-Si/SiO2 multilayers with different a-Si sublayer thicknesses were prepared by plasma enhanced chemical vapour deposition (PECVD). An intermediate phase silicon structure (IPSS), which is intermediate in order between the continuous random network amorphous phase and the well ordered crystalline phase, was discovered in the a-Si sublayers near the crystallization onset temperatures through Raman scattering and cross-section high resolution transmission electron microscopy (HRTEM). A strong broad photoluminescence (PL) band, consisting of two peaks centred at 773 nm and 863 nm respectively, was observed with the formation of the IPSS. Based on the analysis of the temperature dependence of PL, the strong PL emission bands centred at 863 and 773 nm are ascribed to the structural defects inside the IPSS and Si = O at the surface of the IPSS, respectively.

INTERFACE CONSTRAINED GROWTH FOR SIZE CONTROL NANOFABRICATION: MECHANISM AND EXPERIMENTS

We propose a model on the interface constrained growth in a-SiNx/a-Si:H/a-SiNx sandwich structures to make uniform nc-Si grains. Based on the classical growth thermodynamic theory, we study quantitatively the effect of the interface and shape of the nc-Si on the crystal growth in relation to the Gibbs free energy. From our model, we have theoretically determined the critical a-Si sublayer thickness of 34 nm for the interface constrained growth and interpreted the increase of the crystallization temperature in the ultra thin a-Si sublayer. In order to examine the model, a series of samples of a-SiNx/a-Si:H/a-SiNx with a-Si sublayer thickness from 2 nm to 40 nm were fabricated and then annealed at 1000°C, for 30, 120, and 240 min, respectively. The results of microstructure characterization supported our model and indicated that the critical a-Si sublayer thickness is between 20 nm and 40 nm which is coincidence with the theoretical value estimated from our model.

Charging and Coulomb blockade effects in nanocrystalline Si dots embedded in SiO/sub 2/ matrix

By using capacitance-voltage (C-V) and conductance-voltage (G-V) spectroscopy, we studied charging and Coulomb blockade effects in nanocrystalline Si (nc-Si) dots which are embedded in SiO/sub 2/ matrix. Distinct frequency-dependent capacitance and conductance peaks have been observed at room temperature. These experimental results can be explained by resonant tunneling of electrons or holes into the nc-Si dots and Coulomb blockade effect in the nc-Si dots. Experimental results are in agreement with theoretical evaluation based on the model of Coulomb blockade.

Blue emission from hydrogen-containing a-Si:H/SiO2 multilayers and the investigation of its mechanism

A series of hydrogen-containing a-Si:H/SiO2 multilayers with different a-Si:H sublayer thickness were fabricated by layer-by-layer deposition andin situ plasma oxidation in a plasma-enhanced chemical vapor deposition system (PECVD). Optical induced blue emission from the samples was observed by the naked eye at room temperature, which has never been reported in the luminescence study of Si/SiO2 multilayers up to now. Both the photoluminescence (PL) peak and the absorption edge show a blue shift as the a-Si:H sublayer thickness decreases. The origin of the blue emission and the effect of hydrogen are discussed.