The electroluminescence (EL) properties of Er-doped Si nanoclusters (NC) embedded in metal–oxide–semiconductor devices are investigated. Due to the presence of Si NC dispersed in the SiO2 matrix, an efficient carrier injection occurs and Er is excited, producing an intense 1.54 μm room temperature EL. The EL properties as a function of the current density, temperature, and time have been studied in detail. We have also estimated the excitation cross section for Er under electrical pumping, finding a value of ∼1×10−14 cm2. This value is two orders of magnitude higher than the effective excitation cross section of Er ions through Si NC under optical pumping. In fact, quantum efficiencies of ∼1% are obtained at room temperature in these devices.
In this work, the stationary and time-resolved electroluminescence (EL) properties of Si quantum dots embedded within a metal–oxide–semiconductor device are investigated. In particular, we measured the excitation cross section of Si nanocrystals under electrical pumping, finding a value of 4.7×10−14 cm2 which is two orders of magnitude higher with respect to the excitation cross section under 488 nm optical pumping. We also studied the radiative and nonradiative decay processes occurring in these devices by measuring the time evolution of the EL signal. We demonstrate that the mechanism responsible for the emission is the same under both electrical and optical pumping. The overall quantum efficiency of the electrical pumping is estimated to be two orders of magnitude higher than the quantum efficiency for optical pumping in all the studied temperature ranges.
We report the results of a detailed study on the structural, electrical and optical properties
of light emitting devices based on amorphous Si nanostructures. Amorphous nanostructures
may constitute an interesting system for the monolithic integration of optical and electrical
functions in Si ULSI technology. In fact, they exhibit an intense room temperature
electroluminescence (EL), with the advantage of being formed at a temperature of
900 °C, while
at least 1100 °C
is needed for the formation of Si nanocrystals. Optical and electrical properties of
amorphous Si nanocluster devices have been studied in the temperature range between 30
and 300 K. The EL is seen to have a bell-shaped trend as a function of temperature with a
maximum at around 60 K. The efficiency of these devices is comparable to that found in
devices based on Si nanocrystals, although amorphous nanostructures exhibit peculiar
working conditions (very high current densities and low applied voltages). Time resolved
EL measurements demonstrate the presence of a short lifetime, only partially due to the
occurrence of non-radiative phenomena, since the very small amorphous clusters formed at
900 °C
are characterized by a short radiative lifetime. By forcing a current through the device a
phenomenon of charge trapping in the Si nanostructures has been observed. Trapped
charges affect luminescence through an Auger-type non-radiative recombination of excitons.
Indeed, it is shown that unbalanced injection of carriers (electrons versus holes) is
one of the main processes limiting luminescence efficiency. These data will be
reported and the advantages and limitations of this approach will be discussed.
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