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Screening of quantum-confined Stark effect in nitride laser diodes and superluminescent diodes
摘要： In the present work we report on the observation of carrier-induced screening of built-in electric fields in (Al,In)GaN laser diodes and superluminescent diodes. We use the emission peak energy as a measure of the quantum-confined Stark effect and its screening by free carriers. For superluminescent diodes we observe a steady increase of screening up to the current density of 10 kA/cm2. This shows that the lasing in nitride laser diodes occurs under high electric fields, far from the flat band conditions.
关键词： nitride laser diodes,electric fields,carrier screening,quantum-confined Stark effect,superluminescent diodes
更新于2025-11-14 15:24:45
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Stark Effect and Environment-Induced Modulation of Emission in Single Halide Perovskite Nanocrystals
摘要： Organic-inorganic halide perovskites have emerged as promising materials for next generation solar cells. In nanostructured form also, these materials are excellent candidates for optoelectronic applications such as lasers and light emitting diodes for displays and lighting. While great progress has been achieved so far in optimizing the intrinsic photophysical properties of perovskite nanocrystals (NCs), in working opto-electronic devices external factors, such as the effects of conducting environment and of the applied electric field on exciton generation and photon emission have been largely unexplored. Here, we use NCs of the all-inorganic perovskite CsPbBr3 dispersed polyvinyl carbazole, a hole-conductor, and in polymethyl methacrylate, an insulator, to examine the effects of applied electric field and conductivity of the matrix on the perovskite photophysics at single-particle level. We found that the conducting environment causes a significant decrease of photoluminescence (PL) brightness of individual NCs due the appearance of intermediate-intensity emitting states with significantly shortened lifetime. Applied electric field has a similar effect and, in addition, causes a non-linear spectral-shift of the PL maxima, a combination of linear and quadratic Stark effect caused by environment-induced polarity and field-related polarizability. The environment and electric field effects are explained by ionization of the NCs through hole transfer and emission of the resulting negatively-charged excitons.
关键词： ionization,halide perovskite nanocrystals,single-particle spectroscopy,Stark effect,blinking
更新于2025-09-23 15:23:52
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Giant Stark effect in coupled quantum wells: Analytical model
摘要： Coupled quantum wells have been proposed as candidates for highly polarizable structures due to their near-degenerate and dipole-coupled electronic states. Hence, many interesting applications in linear and nonlinear optics can be envisioned. We analyze this proposal considering a simple structure with a delta-function barrier separating the wells. While very substantial Stark shifts are certainly predicted for this geometry, perturbative estimates based on polarizabilities (and hyperpolarizabilities) fail beyond a critical ?eld strength that depends inversely on the barrier. Hence, a giant Stark effect due to near-degenerate states is invariably limited by a small critical ?eld. Our analytical (hyper) polarizability expressions are applied to ?nd quantitative Stark shifts for GaAs quantum wells and transition-metal dichalcogenide bilayers. The predicted Stark shifts and critical ?elds agree with the ?eld dependence observed in a range of available experiments.
关键词： Stark effect,hyperpolarizability,GaAs,transition-metal dichalcogenide bilayers,polarizability,coupled quantum wells
更新于2025-09-23 15:19:57
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Strong Spin-Selective Optical Stark Effect in Lead Halide Perovskite Quantum Dots
摘要： The optical Stark effect (OSE) stems from a coherent, nonlinear interaction between a transition and a non-resonant light field, which usually causes a blue-shift of the transition energy. This shift can be understood using the picture of so-called photon-dressed states or Floquet states. The perturbation induced by a light filed which is periodical in time results in a series of quasi-static Floquet eigenstates periodically spaced in units of the photon energy. The repulsion (hybridization) between the Floquet and equilibrium states causes a blueshift of the transition between the equilibrium states, as schematically shown in Fig. 1a. The OSE effect is intrinsically helicity-selective, that is, a left circularly polarized light couples only to the |0> to |+1> but not the |0> to |-1> transition and vice versa (the number in the ket is the azimuthal quantum number of the total angular momentum). Experimentally, the OSE can be conveniently observed using circularly polarized transient absorption (TA) spectroscopy. With a co-circularly polarized pump-probe configuration, the probe pulse measures a blue-shifted transition in the duration of the pump pulse and a derivative-like difference spectrum (with respect to the unpumped spectrum) can be detected (Fig. 1b), whereas with a counter-circularly polarized configuration nothing can be detected if multi-photon absorption is negligible.
关键词： transient absorption spectroscopy,optical Stark effect,spin-selective,lead halide perovskite,quantum dots
更新于2025-09-23 15:19:57
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Design of Hybrid Plasmonic Multi-Quantum-Well Electro-Reflective Modulators towards < 100 fJ/bit Photonic Links
摘要： Realization of on-board and inter-chip optical interconnects requires a photonic data link with power consumption well below their electrical counterparts (i.e. <<1 pJ/bit). Currently, directly modulating 850 nm vertical cavity surface emitting lasers at >50 Gb/s requires 2-4 pJ/bit/channel. External reverse-biased modulators could drastically reduce this power consumption. Here we design ultralow power GaAs/AlGaAs multi quantum well electro-reflective modulators operating at 1 V for facile integration with polymer “optical bridges”, utilizing coupled quantum confined Stark effect between adjacent quantum wells and optical coupling to hybrid surface plasmon-slab modes for significantly enhanced extinction ratio and spectral bandwidth. Distinctive from conventional electro-optical or electro-absorption modulators, this new design synergistically leverages ultra-large changes in both refractive index (|Δn|~0.05) and absorption coefficient (Δα~104 cm-1), achieving 35-50 dB extinction ratio at 1 V reverse bias with a low insertion loss of 1-3 dB, an incident angle tolerance of ~5°, and a spectral bandwidth of 7-10 nm. The modulator power consumption is ~ 1.9 fJ/bit without the need of thermal tuning, and the RC-limited bandwidth well exceeds 100 GHz. This new modulator enables high bandwidth and ultralow power optical interconnect networks at >100 Gb/s/channel and <100 fJ/bit/channel compatible with ever-scaling CMOS technologies.
关键词： quantum confined Stark effect,Optical interconnections,Optical modulation,surface waves,quantum well devices
更新于2025-09-23 15:19:57
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Sub-Femtosecond Stark Control of Molecular Photoexcitation With Near Single-Cycle Pulses
摘要： Electric fields can tailor molecular potential energy surfaces by interaction with the electronic state-dependent molecular dipole moment. Recent developments in optics have enabled the creation of ultra-short few-cycle optical pulses with precise control of the carrier envelope phase (CEP) that determines the offset of the maxima in the field and the pulse envelope. This opens news ways of controlling ultrafast molecular dynamics by exploiting the CEP. In this work, we show that the photoabsorption efficiency of oriented H2CSO (sulfine) can be controlled by tuning the CEP. We further show that this control emanates from a resonance condition related to Stark shifting of the electronic energy levels.
关键词： ultrafast photochemistry,Ab initio multiple spawning (AIMS),few-cycle pulse,Stark effect,excited state dynamics
更新于2025-09-19 17:15:36
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Estimation of the Lyman- <i>α</i> signal of the EFILE diagnostic under static or radiofrequency electric field in vacuum
摘要： The electric field induced Lyman-α emission diagnostic aims to provide a non intrusive and precise measurement of the electric field in plasma, using a beam of hydrogen atoms prepared in the metastable 2s state. The metastable particles are obtained by means of a proton beam extracted from a hydrogen plasma source, and neutralised by interaction with vaporised caesium. When a 2s atom enters a region where an electric field is present, it undergoes a transition to the 2p state (Stark mixing). It then quickly decays to the ground level, emitting Lyman-α radiation, which is collected by a photomultiplier. The s→p transition rate is proportional to the square of the magnitude of the electric field, and depends on the field oscillation frequency (with peaks around 1 GHz). By measuring the intensity of the Lyman-α radiation emitted by the beam it is possible to determine the magnitude of the field in a defined region. In this work, an analysis of the behaviour of the diagnostic under static or radiofrequency electric field is presented. Electric field simulations obtained with a finite element solver of Maxwell equations, combined with theoretical calculations of the Stark mixing transition rate, are used to develop a model for the interpretation of photomultiplier data. This method shows good agreement with experimental results for the static field case, and allows to measure the field magnitude for the oscillating case.
关键词： Stark effect,plasma diagnostics,electric field measurement,electromagnetic simulations
更新于2025-09-19 17:15:36
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Terahertz-Driven Stark Spectroscopy of CdSe and CdSe–CdS Core–Shell Quantum Dots
摘要： The effects of large external fields on semiconductor nanostructures could reveal much about field-induced shifting of electronic states and their dynamical responses, and could enable electro-optic device applications that require large and rapid changes in optical properties. Studies of quasi-DC electric field modulation of quantum dot (QD) properties have been limited by electrostatic breakdown processes observed under high externally applied field levels. To circumvent this, here we apply ultrafast THz electric fields with switching times on the order of 1 ps. We show that a pulsed THz electric field, enhanced by a microslit field enhancement structure (FES), can strongly manipulate the optical absorption properties of a thin film of CdSe and CdSe:CdS core:shell QDs on the sub-picosecond timescale, with spectral shifts that span the visible to near-IR range. Numerical simulations using a semi-empirical tight binding model show that the band gap of the QD film can be shifted by as much a 79 meV during these timescales. The results allow a basic understanding of the field-induced shifting of electronic levels and suggest electro-optic device applications.
关键词： Stark effect,Quantum Dots,Microslits,Terahertz
更新于2025-09-19 17:13:59
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Coaxial semipolar InGaN/GaN microwire array LED with substantially suppressed efficiency droop
摘要： GaN nano/micro-structure based light-emitting diodes (LEDs) have drawn much attention owing to their potential applications in display and optoelectronics integration. Here, we have fabricated coaxial semipolar InGaN/GaN multiple quantum wells (MQWs) microwire array LED with superior performances in suppressing efficiency droop. The results show that our as-synthesized microwire has two semipolar planes (1 01), and the InGaN/GaN MQWs have superior crystal quality. In addition, the efficiency droop ratio of our device is about 9.7% as the injected current increases from 3 to 100 A/cm2, which is largely declined by 47% compared with that of the conventional polar c-plane LEDs. Meanwhile, the microwire array LED reveals a small wavelength shift (3nm) as the injected current increases from 3 to 23 A/cm2. The effective advances in the device should be attributed to the weaker quantum-confined stark effect of InGaN/GaN MQWs in semipolar plane. This work proposes a high repeatability method to fabricate microwire array LED for future optoelectronic integrated systems.
关键词： LED,Quantum-confined stark effect,Semipolar,GaN microwire array,Efficiency droop
更新于2025-09-16 10:30:52
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[IEEE 2019 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - Udine, Italy (2019.9.4-2019.9.6)] 2019 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - Simulation of quantum dot based single-photon sources using the Schr?dinger-Poisson-Drift-Diffusion-Lindblad system
摘要： The device-scale simulation of electrically driven quantum light sources based on semiconductor quantum dots requires a combination of the (semi-)classical semiconductor device equations with cavity quantum electrodynamics. We present a comprehensive quantum-classical simulation approach that self-consistently couples the (semi-)classical drift-diffusion system to a Lindblad-type quantum master equation. This allows to describe the spatially resolved carrier transport in complex, multi-dimensional device geometries along with the fully quantum-mechanical light-matter interaction in the quantum dot-cavity system. The latter gives access to important quantum optical figures of merit, in particular the second-order correlation function of the emitted radiation. In order to account for the quantum confined Stark effect in the device’s internal electric field, the system is solved along with a Schr?dinger–Poisson problem, that describes the envelope wave functions and energy levels of the quantum dot carriers. The approach is demonstrated by numerical simulations of a single-photon emitting diode.
关键词： quantum-confined Stark effect,device simulation,Single-photon sources,quantum-classical coupling
更新于2025-09-12 10:27:22