Cavity Semiconductor Research Articles

Hybrid metal-semiconductor cavities for multi-band perfect light absorbers and excellent electric conducting interfaces

It is desirable for optoelectronic devices to have the capability to simultaneously achieve excellent optical and electric features. Nevertheless, most investigations were performed separately for photon and electron management. In this work, we numerically propose and demonstrate a hybrid metal-semiconductor interface, which offers multi-band perfect light absorption and simultaneously retains the naturally perfect electrical conductivity of a flat metal film. Multi-band anti-reflection and near-unity light absorption is observed in this hybrid metal-semiconductor cavity based absorber (HMSA). Our results show that, the maximal absorption above 97% and the naturally perfect electric conductivity are realizable, suggesting the capability of providing both excellent optical and electric properties. Optical Mie-like resonances in the semiconductor cavities and the hybrid coupling with plasmonic resonances by the metal resonators cooperatively support strong optical field confinement effects, which eventually create the light trapped in the HMSA. These features indicate a platform wherein excellent electrical conducting and multispectral light absorption are designed for potential optoelectronic applications.

Waveguide-coupled metal-clad cavity with integrated feedback stub

We propose a wavelength-scale metal-clad III–V semiconductor cavity coupled to silicon-on-insulator (SOI) waveguide with integrated feedback stub for external tuning of the Q factor. We consider a typical wavelength-scale metal-clad InP/InGaAs cavity integrated on a SOI waveguide and demonstrate more than 5-fold Q-factor improvement in agreement with that predicted by the coupled-mode theory. From additional thermal analysis, we prove that improved heat dissipation can be realized by engineering the layer thicknesses without sacrificing much of the optical performance.

Scalable Electro-Optic Control of Localized Bistable Switching in Broad-Area VCSELs Using Reconfigurable Funnel Waveguides

A basic challenge in photonics is to reproduce the key functions of electronics, while adding the parallelism and simplified circuitry of optics. One major hurdle is the lack of a generic, diode-like optical element. To address this difficulty, the authors offer proof of principle for a miniaturized optical device capable of being only ``on'' or ``off''. Combining photoinduced optical circuitry in quadratic electro-optic crystals with localized structures in broad-area semiconductor cavities, they create a possible building block for future digital optics.

Recurrent Quantum Scars in a Mesoscopic Graphene Ring.

When coherent charge carriers cross micron-scale cavities, their dynamics can be governed by a few resonant states, also called "quantum scars", determined by the cavity geometry. Quantum scars can be described using theoretical tools but have also been directly imaged in the case of high-quality semiconductor cavities as well as in disordered graphene devices, thanks to scanning gate microscopy (SGM). Here, we discuss spatially resolved SGM images of low-temperature charge transport through a mesoscopic ring fabricated from high-quality monolayer graphene lying on top of hexagonal boron nitride. SGM images are decorated with a pattern of radial scars in the ring area, which is found to evolve smoothly and reappear when varying the charge-carrier energy. The energies separating recurrent patterns are found to be directly related to geometric dimensions of the ring. Moreover, a recurrence is also observed in simulations of the local density of states of a model graphene quantum ring. The observed recurrences are discussed in the light of recent predictions of relativistic quantum scars in mesoscopic graphene cavities.

Anisotropy-Induced Quantum Interference and Population Trapping between Orthogonal Quantum Dot Exciton States in Semiconductor Cavity Systems.

We describe how quantum dot semiconductor cavity systems can be engineered to realize anisotropy-induced dipole-dipole coupling between orthogonal dipole states in a single quantum dot. Quantum dots in single-mode cavity structures as well as photonic crystal waveguides coupled to spin states or linearly polarized excitons are considered. We demonstrate how the dipole-dipole coupling can control the radiative decay rate of excitons and form pure entangled states in the long time limit. We investigate both field-free entanglement evolution and coherently pumped exciton regimes, and show how a double-field pumping scenario can completely eliminate the decay of coherent Rabi oscillations and lead to population trapping. In the Mollow triplet regime, we explore the emitted spectra from the driven dipoles and show how a nonpumped dipole can take on the form of a spectral triplet, quintuplet, or a singlet, which has applications for producing subnatural linewidth single photons and more easily accessing regimes of high-field quantum optics and cavity-QED.

Green's functions technique for calculating the emission spectrum in a quantum dot-cavity system

We introduce the Green's functions technique as an alternative theory to the quantum regression theorem formalism for calculating the two-time correlation functions in open quantum systems at the steady state. In order to investigate the potential of this theoretical approach, we consider a dissipative system composed of a single quantum dot inside a semiconductor cavity and the emission spectrum is computed due to the quantum dot as well as the cavity. We propose an algorithm based on the Green's functions technique for computing the emission spectrum that can easily be adapted to more complex open quantum systems. We found that the numerical results based on the Green's functions technique are in perfect agreement with the quantum regression theorem formalism. Moreover, it allows overcoming the inherent theoretical difficulties associated with the direct application of the quantum regression theorem in open quantum systems.Received: 6 September 2016, Accepted: 5 November 2016; Edited by: J. P. Paz; DOI: http://dx.doi.org/10.4279/PIP.080008Cite as: E A Gómez, J D Hernández-Rivero, H Vinck-Posada, Papers in Physics 8, 080008 (2016)This paper, by E A Gómez, J D Hernández-Rivero, H Vinck-Posada, is licensed under the Creative Commons Attribution License 3.0.

Proposal for a compact design for real-time optical bistability switching via a semiconductor cavity containing quantum wells.

A compact design for semiconductor cavities including coupled AlGaN/AlGaAs quantum wells is proposed for all-optical switching of the bistability process. First, physical and geometrical parameters are optimized to engineer the conducting electrons' energy levels in the quantum wells. Then, finite element simulations based on Schrödinger equations are executed to estimate the states of the charge carriers for AlGaN/AlGaAs as the active region. Next, the optical coupling and pumping fields are applied to the active region to both initiate the bistability and facilitate its real-time control. The Maxwell-Bloch approach based on rotating-wave approximation is employed to analyze the optimal conditions for controlling the behavior of optical bistability (OB). It is found that the threshold of OB can be optimized to have low values by tuning the intensity of coupling fields and the rate of an incoherent pumping field. This provides a fast real-time switching facility to control output intensity of the systems. The proposed scheme could have potential applications in optical memories, in which it is paramount to have active control over the readout of the system's quantum states. Thanks to the high nonlinear response of semiconductors, the featured device would be a prospective candidate for on-chip ultrasubluminal wave propagation studies and narrowband real-time switching and filtering applications.

Optical Energy Transfer and Loss Mechanisms in Coupled Intracavity Light Emitters

Despite the near-unity internal quantum efficiencies (IQEs) demonstrated for GaAs-based light emitters, laser cooling of the ubiquitous $III$ – $V$ semiconductors has not been feasible. The key challenges for $III$ – $V$ optical cooling are the reduced absorption of optical excitation at photon energies well below the bandgap and the strong confinement of light in the high refractive index semiconductors. Here, we investigate the possibility to eliminate the need for light extraction and to eventually relax the requirements of the IQE. This is done using electroluminescence and optical energy transfer within intracavity devices consisting of an AlGaAs/GaAs double heterojunction light emitting diodes and a GaAs p-n-homojunction photodiode enclosed within a single semiconductor cavity. We measure the intracavity energy transfer, i.e., the coupling quantum efficiency (CQE) between the two diodes and estimate loss mechanisms by simultaneously measuring the $IV$ characteristics of the emitter diode and the photocurrent of the absorber diode. The measured CQE of our devices is below 60% due to the mirror, light extraction, nonradiative, and detection losses. While this is far below the state-of-the-art efficiencies, our results suggest that it will be possible to substantially improve the efficiency by adopting the fabrication and design principles used for the best performing photoluminescent emitters.

Single-Mode High-Speed 1.5-μm VCSELs

Single-mode 1.5-μm InP-based vertical-cavity surface-emitting lasers (VCSELs) with a 1.5-λ-long semiconductor cavity and two dielectric distributed Bragg reflectors (DBRs) are presented. The electrical, thermal, and optical characteristics are studied as a function of tunnel junction diameter and for different temperatures ranging from –10 up to 65 °C. Small-signal modulation bandwidths in excess of 21 GHz at room temperature are demonstrated for a DC power consumption below 10 mW. In this paper, the superior dynamic characteristics of these VCSELs are shown by demonstrating operation at data rates up to 50 Gb/s with bit-error-ratio slightly above 10 –12 in back-to-back configuration by nonreturn-to-zero modulation and without any equalization. Neither forward error correction nor digital signal processing was required.

III-nitride tunable cup-cavities supporting quasi whispering gallery modes from ultraviolet to infrared.

Rapidly developing nanophotonics needs microresonators for different spectral ranges, formed by chip-compatible technologies. In addition, the tunable ones are much in demand. Here, we present site-controlled III-nitride monocrystal cup-cavities grown by molecular beam epitaxy. The cup-cavities can operate from ultraviolet to near-infrared, supporting quasi whispering gallery modes up to room temperature. Besides, their energies are identical in large ’ripened’ crystals. In these cavities, the refractive index variation near an absorption edge causes the remarkable effect of mode switching, which is accompanied by the spatial redistribution of electric field intensity with concentration of light into a subwavelength volume. Our results shed light on the mode behavior in semiconductor cavities and open the way for single-growth-run manufacturing the devices comprising an active region and a cavity with tunable mode frequencies.

Tunable photon blockade in coupled semiconductor cavities

In this paper, we show that photon blockade can be observed in a system with weak Kerr nonlinearities. The system consists of two spatially overlapping single-mode semiconductor cavities with tunable one- and two-photon tunneling. We find that both conventional and unconventional single-photon blockades are controllable by manipulating the phase in the hopping regardless of the weakness of nonlinearity. We refer to the photon blockade with weak nonlinearities as an unconventional photon blockade. The unconventional photon blockade effect originates from the destructive interference between different paths from the ground state to two-photon states. We analytically derive the exact optimal conditions for strong antibunching, which are in good agreement with those obtained by numerical simulations. The optimal parameters for photon blockade are derived. Based on these parameters, the semiconductor cavity systems can be used as a single-photon source in regimes of both weak and strong nonlinearities.

Pump-controlled modal interactions in microdisk lasers

We demonstrate an effective control of nonlinear interactions of lasing modes in a semiconductor microdisk cavity by shaping the pump profile. A target mode is selected at the expense of its competing modes either by increasing their lasing thresholds or suppressing their power slopes above the lasing threshold. Despite of strong spatial overlap of the lasing modes at the disk boundary, adaptive pumping enables an efficient selection of any lasing mode to be the dominant one, leading to a switch of lasing frequency. The theoretical analysis illustrates both linear and nonlinear effects of selective pumping, and quantify their contributions to lasing mode selection. This work shows that adaptive pumping not only provides a powerful tool of controlling the nonlinear process in multimode lasers, but also enables the tuning of lasing characteristic after the lasers have been fabricated.

Compact triple coupled quantum well system for electrical/optical control of optical bi/multistability.

Optical bistability (OB) and optical multistability (OM) are investigated in a triple coupled quantum wells system inside a semiconductor cavity sandwiched by distributed Bragg reflector mirrors. By proper manipulation of the optical and electrical parameters, the behaviors of OB and OM can be efficiently controlled. We show that, by tuning the tunneling rates between the quantum wells, the threshold and hysteresis cycle of OB and OM can be engineered. The effect of the incoherent pump field as well as the cooperation parameter on creation of OB is also discussed.

Band gaps induced by vacuum photons in closed semiconductor cavities

We consider theoretically a closed (zero-dimensional) semiconductor microcavity where confined vacuum photonic mode is coupled to electrons in valence band of the semiconductor. It is shown that vacuum-induced virtual electron transitions between valence and conduction bands result in renormalization of electron energy spectrum. As a consequence, vacuum-induced band gaps appear within the valence band. Calculated values of the band gaps are of sub-meV scale, that makes this QED effect to be measurable in state-of-the-art experiments.

Lasing of Coupled Guided Modes in Modified Hollow Hexagonal Semiconductor Cavities

Coupled guided modes, proposed in various modified hollow hexagonal cavities each attached internally to a hexagon, were demonstrated by investigating the laser oscillations in semiconductor cavities. The mode spacing between two adjacent lasing peaks decreased as the size of the internal hexagon increased, due to the increased round-trip length of the coupled guided modes. The linear dependency of the inverse mode spacing to the calculated round-trip length strongly confirmed the lasing of the coupled guided modes. The proposed modes in common-sized external cavities showed resonance structure that could be adjusted widely by controlling the size of the internal hexagon.

Decoherence in semiconductor cavity QED systems due to phonon couplings

We investigate the effect of electron-phonon interactions on the coherence properties of single photons emitted from a semiconductor cavity QED system, i.e. a quantum dot embedded in an optical cavity. The degree of indistinguishability, governing the quantum mechanical interference between two single photons, is calculated as a function of important parameters describing the cavity QED system and the phonon reservoir, e.g. cavity quality factor, light-matter coupling strength, temperature and phonon lifetime. We show that non-Markovian effects play an important role in determining the coherence properties for typical parameter values and establish the conditions under which a Markovian approximation may be applied. The calculations are performed using a recently developed second order perturbation theory, the limits of validity of which are established by comparing to an exact diagonalization approach. We find that for large cavity decay rates the perturbation theory may break down.

Semiconductor cavity QED: Band gap induced by vacuum fluctuations

We consider theoretically a semiconductor nanostructure embedded in one-dimensional microcavity and study the modification of its electron energy spectrum by the vacuum fluctuations of the electromagnetic field. To solve the problem, a non-perturbative diagrammatic approach based on the Green's function formalism is developed. It is shown that the interaction of the system with the vacuum fluctuations of the optical cavity opens gaps within the valence band of the semiconductor. The approach is verified for the case of large photon occupation numbers, proving the validity of the model by comparing to previous studies of the semiconductor system excited by a classical electromagnetic field. The developed theory is of general character and allows for unification of quantum and classical descriptions of the strong light-matter interaction in semiconductor structures.

Preparation of a three-photon state in a nonlinear cavity–quantum dot system

We study theoretically the properties of a three-photon state prepared inside a semiconductor cavity, due to the interaction between a quantum dot and an electromagnetic field, and two consecutive spontaneous parametric downconversion (SPDC) processes. Thus, we consider a scheme involving three modes of the electromagnetic field, whose frequencies are given by the SPDC processes: ω0 → ω1 + ω2 and ω2 → ω1 + ω1. Furthermore, we study the low excitation regime in which a three-photon state is accessible within the system's dynamics.

Cavity enhanced terahertz modulation

We present a versatile concept for all optical terahertz (THz) amplitude modulators based on a Fabry-Pérot semiconductor cavity design. Employing the high reflectivity of two parallel meta-surfaces allows for trapping selected THz photons within the cavity and thus only a weak optical modulation of the semiconductor absorbance is required to significantly damp the field within the cavity. The optical switching yields to modulation depths of more than 90% with insertion efficiencies of 80%.

Delayed feedback control of self-mobile cavity solitons

Control of the motion of cavity solitons is one the central problems in nonlinear optical pattern formation. We report on the impact of the phase of the time-delayed optical feedback and carrier lifetime on the self-mobility of localized structures of light in broad area semiconductor cavities. We show both analytically and numerically that the feedback phase strongly affects the drift instability threshold as well as the velocity of cavity soliton motion above this threshold. In addition we demonstrate that non-instantaneous carrier response in the semiconductor medium is responsible for the increase in critical feedback rate corresponding to the drift instability.