Abstract
Electronic and optoelectronic industries are going through a major paradigm shift for the development of high performance optoelectronic devices to circumvent the global challenges such as, global energy crisis, global warming, environmental toxicity etc. These developments create a huge demand for new functionalities and applications. Progress has been made, but efforts to create a substantial commercial impact still remain. Hybrid nano composites consist of multi component materials with appropriate design can give rise unique properties and multi-functionalities which cannot be seen in a single component material. The objective of this thesis is devoted to design novel optoelectronic devices based on multicomponent materials that can address the global challenges creating an environmental footprint of high performance optoelectronic devices. The results are classified in to several sub-topics, which can be summarized as follows. Photodetector: Electrical Polarization Induced Ultra-high Responsivity Photodetectors Based on Graphene and Graphene Quantum Dots Photodetector is a critical component in optical communication system that is omnipresent in our daily life. Great efforts have been devoted to the development of environmental-friendly photodetectors with high sensitivity, fast response, miniaturization and low cost. In this chapter, we show that many of these limitations can be overcome by integrating the high absorption efficiency of graphene quantum dot (GQD) produced from plants, the high conductivity of graphene, and the permanent polarization of piezoelectric substrate. With the assistance of the electric field provided by the piezoelectric substrate, the photogenerated charges in the GQD can be preferably transferred to the conductive graphene layer. It is found that the photoresponsivity of the device can be enhanced by more than 100 times and the response time is 10 times faster than the current photodetectors. With the ease of tunable properties of GQDs and their availability from plants, we expect our approach will contribute to the further development of green photodetectors with high sensitivity and wide spectral response. Light Emitting Diode (LED): Electrically Driven White Light Emission from Intrinsic Metal–Organic Framework Light emitting diodes (LEDs) have drawn tremendous potential as a replacement of traditional lighting owing to its low power consumption and longer lifetime. Nowadays, the practical white light LEDs (WLED) are contingent on the photon down conversion of phosphors containing rare-earth elements, which limits its utility, energy and cost efficiency. In order to resolve the energy crisis and to address the environmental concerns, designing a direct WLED is highly desirable and remains a challenging issue. To circumvent the existing difficulties, in this report, we have designed and demonstrated a direct WLED consisting of a strontium-based metal-organic framework, {[Sr(ntca)(H2O)2]·H2O}n (1), graphene and inorganic semiconductors, which can generate a bright white light emission. In addition to the suitable design of a MOF structure, the demonstration of electrically driven white light emission based on a MOF is made possible by the combination of several factors including the unique properties of graphene and the appropriate band alignment between the MOF and semiconductor layer. Because electroluminescence using a MOF as an active material is very rare and intriguing and a direct WLED is also not commonly seen, our work here therefore represents a major discovery which should be very useful and timely for the development of solid state lighting. All Graphene Based Optoelectronic Device: Dirac-point Induced Ultralow-threshold Laser Action and Giant Optoelectronic Quantum Oscillations Derived from all Graphene Based Heterojunctions The occurrence of zero effective mass of electrons at the vicinity of the Dirac-point is expected to create new paradigms for scientific research and technological applications, but the related discoveries are rather limited. Here, we demonstrate that a simple architecture composed of graphene quantum dots (GQDs) sandwiched by two graphene layers can exhibit several unprecedented features, including the Dirac-point induced ultralow-threshold laser action, giant peak-to-valley ratio (PVR) with ultra-narrow spectra of negative differential resistance (NDR) and quantum oscillations of current as well as light emission intensity. In particular, the threshold of only 12.4 nA/cm2 is the lowest value ever reported in all kinds of electrically driven lasers, and the PVR value of more than 100 also sets the highest record compared with all reports on graphene based devices. We show that all these new phenomena can be interpreted well based on the unique properties of the band structure of GQD and graphene as well as resonant quantum tunneling. Our findings can be extended to other nano-structural systems and open a route for the development of highly efficient light emitting diodes, lasers and many not-yet-realized nano-electronic applications. A Highly Efficient Single Segment White Random Laser Production of multi-color or multiple wavelength lasers over the full visible-color spectrum from a single chip device has widespread applications, such as super-bright solid state lighting, color laser displays, light based version of Wi-Fi (Li-Fi), and bio-imaging etc. However, designing such lasing devices remains a challenging issue owing to the material requirements for producing multi-color emissions and sophisticated design for producing laser action. Here we demonstrate a simply design and highly-efficient single segment white random laser based on solution processed NaYF4:Yb/Er/Tm@NaYF4:Eu core-shell nanoparticles assisted by Au/MoO3 multilayer hyperbolic metamaterials. The multi-color lasing emitted from core-shell nanoparticles covering the red, green, and blue, simultaneously, can be greatly enhanced by the high-k modes with a suitable design of hyperbolic metamaterials, which enables to decrease the energy consumption of photon propagation. As a result, the energy upconversion emission is enhanced by ~ 50 times with a drastic reduction of lasing threshold. The multiple scatterings arising from the inherent nature of the disordered nanoparticle matrix provide a convenient way for the formation of closed feedback loops, which is beneficial for the coherent laser action. The experimental results were supported by the electromagnetic simulations derived from the finite-difference time-domain (FDTD) method. The approach shown here can greatly simplify the design of laser structures with color-tunable emissions, which can be extended to many other material systems. Together with the characteristics of angle free laser action, our device provides a promising solution towards the realization of many laser-based practical applications.