Dongke Li

Time-resolved and temperature-dependent photoluminescence study on phosphorus doped Si quantum dots/SiO 2 multilayers with ultra-small dot sizes

Light emission from Si quantum dots has been extensively studied but the emission wavelength is usually in the visible range, which is not compatible with the requirements of today’s optical telecommunications. Recently, the light emission in the near-infrared range from impurity-doped Si quantum dots were reported but the light emitting mechanism is still an open question. Here we systematically study the phosphorus doping induced sub-band light emission centered at 1250nm in addition to the conventionally observed 890nm emission band in Si quantum dots/SiO2 multilayers with ultra-small dot sizes. It is found that the photoluminescence behaviours of the two independent emission bands are quite different and strongly influenced by the doping concentrations. The time-resolved photoluminescence measurements demonstrate that the 1250nm band has a much shorter lifetime than the 890nm band, which indicates that it has a higher recombination rate to get an efficient emission. Additionally, the temperature dependent photoluminescence measurements are also used to determine the origin of the 1250nm emission.

The phosphorus and boron co-doping behaviors at nanoscale in Si nanocrystals/SiO2 multilayers

Phosphorus (P) and Boron (B) co-doping effects at the nanoscale in Si nanocrystals/SiO2 multilayers have been studied in the present work. Several interesting experimental results are achieved which are in contrast to the case in bulk-Si and the previous observations on the doped Si nanocrystals. It is found that all the co-doping samples are n-type regardless of B doping ratios. The P doping efficiency in Si NCs is higher than B dopants, and it can be improved via B co-doping with suitable levels. Raman and ESR spectra indicate that the different occupation preferences of P and B in Si NCs are responsible for the interesting co-doping behaviors. It looks like that the electronic structures and the physical properties of Si NCs can be modulated via the impurities co-doping approach.

Modulation of surface states by phosphorus to improve the optical properties of ultra-small Si nanocrystals

Here, we report the enhanced luminescence and optical gain by appropriate P-doping in Si nanocrystals (NCs)/SiO2 multilayers with ultra-small size of ∼1.9 nm. The luminescence intensity is enhanced by 19.4% compared to that of an un-doped NC and the optical gain is as high as 171.8 cm-1, which can be attributed to the reduction of surface defect states by the passivation of P impurities as revealed by electron spin resonance spectra. Further increasing the P-doping ratios results in the increase of conduction electrons due to the substitutional doping of phosphorus in the Si NCs, which favors the Auger recombination process. Consequently, both the luminescence intensity and the optical gain decrease rapidly. It is demonstrated that introduction of the suitable impurities can effectively modulate the surface chemical environment of Si NCs, which provides a new way to control the physical properties of Si NCs.

Si nanocrystals-based multilayers for luminescent and photovoltaic device applications

Low dimensional Si materials have attracted much attention because they can be developed in many kinds of new-generation nano-electronic and optoelectronic devices, among which Si nanocrystals-based multilayered material is one of the most promising candidates and has been extensively studied. By using multilayered structures, the size and distribution of nanocrystals as well as the barrier thickness between two adjacent Si nanocrystal layers can be well controlled, which is beneficial to the device applications. This paper presents an overview of the fabrication and device applications of Si nanocrystals, especially in luminescent and photovoltaic devices. We first introduce the fabrication methods of Si nanocrystals-based multilayers. Then, we systematically review the utilization of Si nanocrystals in luminescent and photovoltaic devices. Finally, some expectations for further development of the Si nanocrystals-based photonic and photovoltaic devices are proposed.