Resumen de Si nanocrystal mos-led's. Strategies to improve efficiency and device lifetime
Mariano José Peralvarez Barrera
The most important challenge of state-of-the-art photonics is to increase the competitives by achieving cost, size and performance levels ell beyond even todays technology. To do this, the optoelectronic integration in smart and low-dimensional system is mandatory.
At present, the only viable technology for on-chip integration is the hybrid technology that combines the best performing III-V light sources and CMOS devices onto a common silicon platform. These heterogeneous structures have recently yielded very interesting results; however, the high cost of photonic components together with the current incompatibilities between III-V and CMOS technologies are a major obstacle to their deployment in most applications.
A more desirable solution is the integration of Si based photonic and electronic devices onto the same platform. This monolithic integration takes advantage of the large expertise on CMOS technology and methods, which undoubtedly translates into a significant reduction of the cost-per-function. CMOS technology has demonstrated by far its suitability for fabricating a wide variety of passive and active photonic devices, such as waveguides, optic modulators, detectors, etc. However achievement of efficient Si-based light sources still is an unresolved matter and many different strategies are currently followed to turn silicon (and silicon-based compounds) into an efficient light emitter and to make someday all-silicon optical systems a reality. Among them, a popular approach is the fabrication of nanometric silicon particles in embedded in dielectric matrices, being silicon oxide the most widely used. The couple Si-nanocrystals/SiO2 shows high chemical and thermal stability, and takes advantage of the improved emission efficiency of quantum confined Si.
In spite of the promising results, however, Si nanocrystal (Si-nc) based devices, unlike mainstream III-V LED's, have had to deal for more than one decade with three (a priori) unsolvable problems: (1) Devices typically exhibit low emission efficiencies, which stems from the concurrence of a deficient excitation of the Si-nc and relatively high leakage currents. (2) The luminescence from Si-nc in SiO2 materials is spectrally restricted to the red-infrared range, within which only a small room for emission tuning is avaible by modifying the Si-nc size. (3) Most devices operate under DC (direct current) polarization and the emission is achieved by impact ionization, on mechanism that is commonly related to fast degradation.
In this thesis, we report on a handful of different strategies and techniques to overcome these inherent limitations. We will show that, in some cases, the device performance can be significantly improved, thereby enabling the incorporation of such Si-nc based devices into more complex applications.
