Hideo Iwase

Analysis of the Purcell effect in photonic and plasmonic crystals with losses

We study the spontaneous emission rate of emitter in a periodically patterned metal or dielectric membrane in the picture of a multimode field of damped Bloch states. For Bloch states in dielectric structures, the approach fully describes the Purcell effect in photonic crystal or spatially coupled cavities with losses. For a metal membrane, the Purcell factor depends on resistive loss at the resonant frequency of surface plasmon polariton (SPP). Analysis of an InP-Au-InP structure indicates that the SPPs Purcell effect can exceed a value of 50 in the ultraviolet. For a plasmonic crystal, we find a position-dependent Purcell enhancement with a mean value similar to the unpatterned membrane.

GaN-based surface-emitting laser with two-dimensional photonic crystal acting as distributed-feedback grating and optical cladding

We demonstrate GaN-based distributed-feedback surface-emitting lasers grown on sapphire substrates with a two-dimensional (2D) square-lattice photonic crystal (PhC) that forms a high-aspect-ratio void array (void diameter: 65 nm and depth: 220 nm). The 2D PhC layer acts as both distributed-feedback grating and p-type optical cladding of a separate confinement heterostructure. To form the 2D PhC in the nitride semiconductor layers, we developed an embedding process that uses mass-transport phenomena. Crystallographic facets appeared on the inner walls of the embedded voids. Room-temperature lasing action was observed at 406.0 nm for a PhC lattice constant of 162.5 nm. The threshold current density was 9.7 kA/cm2 for a 120-μm-square p-contact electrode.

Spontaneous emission control in high-extraction efficiency plasmonic crystals

We experimentally and theoretically investigate exciton-field coupling for the surface plasmon polariton (SPP) in waveguide-confined (WC) anti-symmetric modes of hexagonal plasmonic crystals in InP-TiOAu-TiO-Si heterostructures. The radiative decay time of the InP-based transverse magnetic (TM)-strained multi-quantum well (MQW) coupled to the SPP modes is observed to be 2.9-3.7 times shorter than that of a bare MQW wafer. Theoretically we find that 80 % of the enhanced photoluminescence (PL) is emitted into SPP modes, and 17 % of the enhanced PL is redirected into WC-anti-symmetric modes. In addition to the direct coupling of the excitons to the plasmonic modes, this demonstration is also useful for the development of high-temperature SPP lasers, the development of highly integrated photo-electrical devices, or miniaturized biosensors.

Electrical properties of indium-tin oxide films deposited on nonheated substrates using a planar-magnetron sputtering system and a facing-targets sputtering system

Distribution of the electrical properties of indium-tin oxide (ITO) film prepared by both a planar-magnetron sputtering system (PMSS) and a facing-targets sputtering system (FTSS) at room temperature were investigated. It was found that the outstanding non-uniformities of the electrical properties in noncrystalline ITO films are mainly due to the variation of the oxygen stoichiometry dependent on film positions on substrate surfaces. Furthermore, ITO film with uniform distribution of electrical properties was obtainable using FTSS.

Spontaneous Emission Control in a Plasmonic Structure

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.

Polarized spontaneous emission from an emitter in controlled nodal vacuum fluctuations near a single high reflector

Polarization-dependent spontaneous emission (SE) from multiple quantum wells (MQWs) sandwiched between a high-reflectivity distributed Bragg reflector (DBR) and a low-reflectivity surface of about 30% reflectance was investigated. In photoluminescence spectra, a split of the p- and s-polarized emission peaks was observed at the DBR band edges, while emission was completely suppressed in its bandgap. Theoretical analysis of the SE rate, based on quantum electrodynamics, explains well the experimental observations; that is, SE enhancement ratios of polarized light can be varied drastically by shifting the position of the low-reflectivity surface that modifies the nodal vacuum fluctuations in front of the high reflector.

Fine Crystallographic Facets of Photonic Crystal Voids Embedded in GaN-Based Semiconductor by Mass Transport

We developed a technique for fabricating photonic crystal (PhC) voids embedded in GaN by dry etching, mass transport, and annealing. We report the annealing conditions and shape of the embedded PhC voids. After dry etching to pattern PhC air holes, they are fully capped with a flat GaN layer (34 nm thick) by annealing at 1025 °C. Inner void walls exhibit GaN crystallographic facets. Upon annealing at 900 °C, the air holes are not capped and instead become narrower with increasing annealing duration. Hence, both the shape and diameter can be controlled in the fabrication of PhC structures in GaN.

GaN-based distributed-feedback surface-emitting laser with embedded two-dimensional photonic crystal fabricated by mass-transport technique

We report on GaN-based distributed-feedback surface-emitting lasers on a sapphire substrate. Two-dimensional photonic crystal gratings in our device were embedded into GaN-based structures by mass-transport phenomena. We have observed room-temperature pulsed lasing at 406.0 nm.

Analysis of the spontaneous emission rate enhancement by surface plasmons in a thin metallic layer embedded in semiconductor

We study the modification of spontaneous emission rates from multi-quantum wells beneath a thin metallic layer embedded in semiconductor.