Abstract
Size mismatches between electronics and photonics have been a huge barrier to realize on-chip optical communications and computing systems. The minimum size of conventional semiconductor lasers utilizing dielectric cavity resonators is governed by the optical diffraction limit (λ/2n)3. The recent surge of research interest in nanoplasmonics has been largely due to its capability to break the diffraction limit. In this dissertation, we present a record smallest semiconductor nanolaser based on surface plasmon amplification by stimulated emission of radiation (spaser). In plasmonic cavities, the coupling of photons and plasmons (a hybrid system) on noble metal surfaces at optical frequencies constitutes the necessary spaser feedback mechanism. However, direct observation of spaser has not been conducted. Only the far-field radiation (lasing) of spaser (so-called plasmonic nanolasers) was observed, and the plasmonic nanolaser emissions were first spectrally and temporally resolved in this study. In Chapter 1, the background context of photonic and plasmonic nanolaser research is provided. The theoretical background of spaser is also briefly described. In Chapter 2, the related experimental techniques are presented to explore the lasing features of nanolasers. In Chapters 3 and 4, the non-polar nitride semiconductor (InGaN) nanorods with highly crystalline quality is discussed, grown using plasma-assisted molecular beam epitaxy (PAMBE), served as efficient gain media for realizing plasmonic nanolasers. Chapter 4 presents a plasmonic nanolaser consisting of an epitaxial growth silver film coupled with a single epitaxial growth InGaN/GaN nanorod. Nevertheless, overcoming the losses inherent to metals remains a fundamental challenge. The epitaxial approach reported in this study provides a scalable platform for low-loss, active nanoplasmonics. Therefore, 3D diffraction-unlimited nanolasers were realized and operated in continuous-wave conditions, above liquid nitrogen temperature, and in a nearly 100% polarized lasing mode. According to theoretical studies, a large proportion of energy emissions are transformed into in-plane directional and coherent surface plasmon (as a spaser). In Chapter 5, we introduce the single-mode, all-color plasmonic nanolasers. By optimizing the metal-oxide-semiconductor (MOS) structure design, nanolasers exhibiting an ultralow threshold can be fabricated. The temporal coherence signature denotes the “thresholdless” blue plasmonic nanolaser. In Chapter 6, the electrical properties of axial p–n junctions in GaN nanorods are described; the results indicate that nitride semiconductors are a prerequisite for electrically driven photonic devices in the future. Chapter 7 presents a single InGaN nano light emitting diode (LED) that comprises a single InGaN nanodisk embedded in a GaN p-n nanorod. This nano-LED can be used as a subwavelength light source that possesses spatial, spectral, and polarization controlling capabilities, which are crucial for extending optical imaging and lithography beyond the diffraction limit. In this study, the growth of high-quality nitride semiconductor nanorods by using PAMBE offered several advantages for broadband-tunable light emission in the full visible spectrum and amphoteric doping (for both n- and p-type GaN) for solid state lighting. Therefore, electrically driven nitride semiconductor-based plasmonic nanolasers are expected to be employed in multi-functional on-chip optoelectronic devices in the near future.