Nanoscale Photonics and Optoelectronics

Surface plasmon polaritons (SPPs) are electromagnetic waves at optical frequencies that propagate at the surface of a conductor [1]. SPPs can trap optical photons far below their diffraction limit. The field confinement of SPP provides the environment for controlling the interaction between light and matter. In this chapter, we discuss the quantum electrodynamics (QED) of SPP coupling of excitons near a metal-layer surface, and an exciton embedded in a metal microcavity. We analyze the enhanced spontaneous emission (SE) rate of the exciton coupled to a large number of SPP modes near a uniform or periodically patterned metal layer traveling with extremely slow group velocities. Combining the effects of quality factor (Q) and ohmic losses for each SPP mode, we explain how various loss mechanisms affect the SE rate of excitons in such structures. Similarly, we consider the Q-factor and mode volume of a cavity mode formed by a defect in a grating structure and again investigate the enhancement of SE for excitons lying in a metal cavity. Because defect cavity designs confine modes in all three dimensions, we observe that such a structure of extremely small mode volume could reach various regimes of cavity quantum electro-dynamics (cavity QED). Controlling the SE properties of emitters through the exciton–SPP coupling is great promise for new types of opto-electronic devices overcoming the diffraction limit.

A novel method to enhance light emission efficiencies from solid-state materials was developed by the use of surface plasmon (SP). A 17-fold increase in the photoluminescence (PL) intensity along with a 7-fold increase in the internal quantum efficiency (IQE) of light emission from InGaN/GaN quantum wells (QWs) was obtained when nanostructured silver layers were deposited 10 nm above the QWs. A 32-fold increase in the spontaneous emission rate of InGaN/GaN at 440 nm probed by the time-resolved PL measurements was also observed. Likewise, both light emission intensities and rates were enhanced for organic materials, CdSe-based nanocrystals, and also Si/SiO₂ nanostructures. These enhancements should be attributed to the SP coupling. Electron–hole pairs in the materials couple to electron vibrations at the metal surface and produce SPs instead of photons or phonons. This new path increases the spontaneous emission rate and the IQEs. The SP-emitter coupling technique would lead to super bright and high-speed solid-state light-emitting devices that offer realistic alternatives to conventional fluorescent light sources.

Cavity polaritons which are the elementary optical excitations in semiconductor microcavities may be viewed as a superposition of excitons and cavity photons. The major feature of cavity polariton technology centers on large and unique optical nonlinearities which would lead to a new class of optical devices such as polariton lasers exhibiting very low thresholds and polariton parametric amplifiers with ultrafast response. Among the wide bandgap semiconductors, GaN and ZnO are promising candidates for low-threshold polariton lasers operating at room temperature because of their large oscillator strengths and large exciton binding energies, particularly ZnO with its unmatched exciton binding energy of 60 meV. In this chapter, the recent progress on polariton devices based on wide bandgap semiconductor microcavities is reviewed.

In this chapter, regular and inverse synthetic opals are examined experimentally by infiltrating them with CdSe quantum dots (QDs). Confocal microscopy measurements in which we track the infiltration of QDs inside the regular and inverse opals show indications of focusing of light emitted by QDs, which can be due to negative refraction occurring at the opal–glass interface. The formation of a focus can be an indication of the left-handed behavior of these synthetic opals in the [111] direction in its higher photonic band, above the photonic band gap (PBG). This result can be very promising because, until now, left-handed behavior has not been demonstrated in 3D photonic crystals in the visible region of light. This result was made possible due to the use of infiltrated QDs as internal light sources inside the porous photonic crystal, which appears to be a very useful technique for the study of other negative-index materials (NIM) effects.

The semiconductor industry has seen a remarkable miniaturization trend, driven by innovations in nanofabrication and nanoscale characterization [1]. Semiconductor technology can currently manufacture devices with feature size less than 100 nm. A modern microprocessor can have more than 500 million transistors. Electronic integrated circuits are inherently single-channel connected device arrays within a two-dimensional printed circuit board [2]. By further shrinking transistor size, one approaches the technical, physical, and economical limits, which will be reached within a few years [3]. At the same time, the insulating layer is also getting thinner leading to an enhancement in the current leakage and resulting in short circuit [4]. Manufacture cost increases drastically with further size reduction. As this trend is likely to yield faster and compact electronic and photonic devices, the size of microelectronic circuit components will soon need to reach the scale of atoms or molecules [1]. Those limitations and application requirements inspired extensive research aimed at developing new materials, device concepts, and fabrication approaches that may enable the integrated devices to overcome the limitations of the conventional microelectronic technology. This will require a conceptual design of new device structures beyond CMOS technology which may require alternative materials to overcome these limits. Hybrid organic–inorganic system is one of the alternative solutions.

Optical limiters are nonlinear materials that exhibit a drop in transmittance as the energy of incident laser pulses increases, usually above a certain threshold. They have the potential for protecting optical sensors, and possibly even human eyes, from laser pulse damage. The problem of optical power limiting has been a subject of increasing interest for more than two decades now. The interest is due to the increasingly large number of applications based on lasers that are currently available. Several research groups have been attempting to develop novel OPL materials based on nonlinear optical (NLO) chromophores. As a result, there are a large number of publications and patents on this subject. Some of the best-performing optical limiters are materials containing carbon nanotubes (CNTs); however, such materials are difficult to prepare and have problems with stability. In this chapter, the origin of OPL as well as the mechanism of OPL has been discussed. Ways to modify CNTs and to make them suitable for OPL applications have also been discussed.

We review the growth and field emission (FE) properties of ZnO, ZnS, and GaN nanostructures. For ZnO nanostructures, we discuss in detail solution-based growth techniques and the effects of residual gas exposure on the FE properties. We present new results showing that O₂ and CO₂ exposures do not have a significant effect on the FE properties of ZnO nanorods, but N₂ exposure significantly degrades them. We also present new results showing that Cs deposition significantly improves the FE properties of GaN nanorods.

A comprehensive study, including growth, optical characterization and anisotropic transport in quantum well (QW), quantum wire (QWr), and quantum dot (QD) systems, is carried out for the InAs/InP nanostructures grown by gas-source molecular beam epitaxy on InP (001) substrates. Role of substrate misorientation in the self-organized formation, shape, and alignment of InAs nanostructures is investigated. The emission and absorption properties related to interband transitions of the InAs/InP nanostructures are studied by means of polarization-dependent photoluminescence (PL) and transmission spectroscopy. It is demonstrated that the emission wavelength of grown nanostructures extends up to 2 μm, including the technologically important 1.3 μm and 1.55 μm, at room temperature. Polarization-dependent PL and transmission measurements for all QWrs and QDs reveal much similarity in temperature behavior in spite of a qualitatively different character of the one (1D)- and zero (0D)-dimensional density-of-states functions. The in-plane transport of electrons and holes in QWrs, QDs, and QWs is investigated and interpreted in terms of anisotropic two-dimensional carrier systems, and in terms of coupled 1D or 0D systems. Peculiar band structure and carrier relaxation in the InAs/InP nanostructures suggest currently the large application potential for the optical devices – mainly for the telecommunication wavelength of 1.55 μm.