ABSTRACT
In semiconductor technologies the geometric miniaturization of individual components and the development of multi-function devices have been scaling according to “Moore’s Law.” On the other hand, the miniaturization of photonic components such as waveguides, emitters, and switches is a totally different matter as it is limited by the diffraction of light. For instance, diode lasers and optical guided wave structures must confine the light within their cavities and core layers, respectively, so that the minimum feature sizes of these optical structures are limited to around one wavelength. The waveguides mostly used in today’s photonics are low index contrast optical fibers, which have a cross-section of tens of dielectric wavelengths squared, with extensions that are several thousands of wavelengths for a device such as a coupler. There are also integrated photonic circuits with high index contrast waveguides. However, the minimal lateral field confinement of these systems is still approximately one dielectric wavelength, and the length of a coupler is several hundreds of wavelengths. Waveguide couplers based on refractive-indexmodulation photonic crystals, reducing this length to tens of wavelengths, have been fabricated.[1, 2] However, the lateral feature of these becomes significantly increased to several dielectric wavelengths in order to establish the Bragg boundary. This imposes severe limitations on packing density and construction of high-density photonic integrated circuits needed for future photonics. Those will require increased integration of photonic devices of up to 1000×1000 input and output channels on a single substrate for increased data transfer rates and for improved photolithography with feature lengths well below one wavelength.[3]
By the unique physical properties thus discussed, exciton and exciton-polariton in quantum dots (QDs) have already become an enabling science in the form of optoelectronics and in many application fields such as photonics (including optical information technology), health care, life sciences, displays, security, sensing, lighting, materials science, and manufacturing. In this chapter, we present major optoelectronic devices based on nanostructures at the electronic and photonic engineering levels. Despite the extensive and successful research and technical development in this area both fundamental and technical difficulties remain to be solved. The major fundamental difficulty is that the unique optical properties of
excitons and exciton-polaritons in nanostructures are based on quantum confinement, whereas for all practical applications we need to have direct interactions between excitons in nanostructures and the external circuit. For example, it is difficult to extract carriers from QDs into the circuit in solar cells. Confined excitons in nanostructures, by definition, are completely surrounded by insulating materials and a direct conducting path would break the confinement responsible for their special properties.
