All-inorganic lead-halide perovskite (CsPbX3, X = Cl, Br, I) quantum dots (QDs) have emerged as a competitive platform for various optoelectronic applications e.g., LEDs featuring narrow emission and quantum light sources. Many-body interactions and quantum correlations among photogenerated exciton complexes play an essential role, e.g., by determining the laser threshold, the overall brightness of LEDs, and the single-photon purity in quantum light sources. In this work, by combining single-QD optical spectroscopy performed at cryogenic temperatures in combination with configuration interaction (CI) calculations, we address the trion and biexciton binding energies and unveil their peculiar size dependence. We find that trion binding energies increase from 7 meV to 17 meV for QD sizes decreasing from 30 nm to 9 nm, while the biexciton binding energies increase from 15 meV to 30 meV, respectively. CI calculations quantitatively corroborate the experimental results and suggest that the effective dielectric constant for biexcitons slightly deviates from the one of the single excitons, potentially as a result of coupling to the lattice in the multiexciton regime. Our findings provide a deep insight into the multiexciton properties in all-inorganic lead-halide perovskite QDs, essential for classical and quantum optoelectronic devices.
The contribution focuses on a theoretical analysis of 2D multilayered halide perovskites, and their interfaces with 3D perovskites. At present, perovskite materials are mixed with each other in complex alloys and heterostructures, including 2D/3D compositions, combined with additives or protecting layers to improve their stability as well as assembled with carrier selective layers. The specificities of the mechanical properties of halide perovskites by comparison to classical semiconductors and the role played by large cations in the interlayer of the 2D perovskite are discussed.
We present the first steps toward the development of MoS2/Si heterojunctions photovoltaics, essentially for integrated photonic devices applications.
Therefore, we conjugate numerical device simulation, optical and structural characterizations, and density functional theory calculations. Through numerical device simulation, we show the potential of such solar cells, with attainable power conversion efficiencies of about 20%. Optical and structural characterizations of thin 2H-MoS2 layers deposited on SiO2 80nm/Si (001) substrates provides a path for the optimization of the 2D MoS2 material. With DFT calculations, we open the door for the optimization of the MoS2/Si interface, which is crucial for the device performances.
Perovskite-based solar cells (PSCs) have opened the possibility of cost-effective, high-efficiency photovoltaic conversion. However, their instabilities prevent them from commercialization. One of the instability triggers has been attributed to the mobile ions flowing into the carrier transport layer(s). To study the effect of this ionic migration, a numerical PSC model is developed, considering electronic and ionic mixed drift-diffusion transport both in the perovskite and the hole transport layer. The inverted PSC architecture, phenyl-C61-butyric acid methyl ester (PCBM)/perovskite/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) with two heterojunctions, is analyzed. The effect of the ionic migration on the performance of the PSCs has been analyzed by (1) the variation of the ionic mobile concentration and (2) the modification of the local trapping density. The current–voltage (J–V) and capacitance–voltage characteristics show that the electric field in the bulk can be screened by the ionic distribution modifying the effective built-in voltage. At high ionic concentrations, the electric field at the interfaces is also affected, hindering the charge extraction. The simulations show that the short circuit current is therefore strongly modified.
Despite the wealth of research conducted the last three years on hybrid organic perovskites (HOP), several questions remain open including: to what extend the organic moiety changes the properties of the material as compared to allinorganic (AIP) related perovskite structures. To ultimately reach an answer to this question, we have recently introduced two approaches that were designed to take the stochastic molecular degrees of freedom into account, and suggested that the high temperature cubic phase of HOP and AIP is an appropriate reference phase to rationalize HOP’s properties. In this paper, we recall the main concepts and discuss more specifically the various possible couplings between charge carriers and low energy excitations such as acoustic and optical phonons. As available experimental or simulated data on low energy excitations are limited, we also present preliminary neutron scattering and ultrasonic measurements obtained and freshly prepared single crystals of CH3NH3PbBr3.
A method based on DFT is used to obtained dielectric profiles. The high frequency Ɛ∞(z) and the static Ɛs(z) dielectric profiles are compared for 3D, 2D-3D and 2D Hybrid Organic Perovskites (HOP). A dielectric confinement is observed for the 2D materials between the high dielectric constant of the inorganic part and the low dielectric constant of the organic part. The effect of the ionic contribution on the dielectric constant is also shown. The quantum and dielectric confinements of 3D HOP nanoplatelets are then reported. Finally, a numerical simulation based on the SILVACO code of a HOP based solar cell is proposed for various permittivity of MAPbI3.
KEYWORDS: Optoelectronics, Spintronics, 3D modeling, Nanostructures, Optoelectronic devices, Photovoltaics, Transistors, Metals, Lead, Tin, Perovskite, System on a chip, Quantization, Solar cells, Semiconductors, Light emitting diodes, Control systems
In this paper, we propose a description of the Rashba-Dresselhaus effect in Hybrid Organic Perovskite (HOP). We show how the loss of the inversion symmetry leads to the loss of the spin degeneracy. An example of structure where both Rashba and Dresselhaus operate is illustrated with the formamidinium tin iodide CH(NH2)2SnI3. The control of this effect is as well addressed by two examples. A first example concerns the control with the temperature and is demonstrated for the 2D HOP Bz2PbCl4 (Bz = benzylammonium). Then the control with an external field is established for the 3D HOP CH3NH3PbBr3.
In this paper, we examine recent theoretical investigations on 3D hybrid perovskites (HOP) that combine concepts developed for classical bulk solid-state physics and empirical simulations of their optoelectronic properties. In fact, the complexity of HOP calls for a coherent global view that combines usually disconnected concepts. For the pseudocubic high temperature reference perovskite structure that plays a central role for 3D HOP, we introduce a new tight-binding Hamiltonian, which specifically includes spin-orbit coupling. The resultant electronic band structure is compared to that obtained using state of the art density functional theory (DFT). Next, recent experimental investigations of excitonic properties in HOP will be revisited within the scope of theoretical concepts already well implemented in the field of conventional semiconductors. Last, possible plastic crystal and orientational glass behaviors of HOP will be discussed, building on Car-Parrinello molecular dynamics simulations.
This paper reviews some of the recent theoretical investigations on the Rashba Dresselhaus spin effects and dielectric properties of CH3NH3PbI3 hybrid perovskites and CsPbI3 all-inorganic perovskites using Density functional theory. The spin vectors rotate in the non-centrosymmetric P4mm tetragonal phase, respectively clockwise and counterclockwise, in a manner that is characteristic of a pure Rashba effect. The high frequency dielectric constants ε∞ of MAPbI3 and CsPbI3 are similar as anticipated, since large differences are only expected at very low frequency where additional contributions from molecular reorientations show off for the hybrid compounds. A first simulation of a perovskite on silicon tandem cell, including a tunnel junction, is also investigated. Effect of halogen substitution (I/Br) is inspected, revealing limitations for short-circuit current and open-circuit voltage electrical characteristics.
This work theoretically studies the impacts of the inhomogeneous broadening on the modulation dynamics of quantum dot lasers using a multi-population rate equation model. The modulation dynamics shows two distinct regimes depending on the energy separation between the GS and the ES. For broadenings smaller than the GS-ES separation, the K-factor increases while the damping factor offset, the differential gain and the gain compression factor decrease with the inhomogeneous broadening. For broadenings larger than the GS-ES separation, the damping factor offset keeps almost constant while the K-factor, the differential gain and the gain compression factor increases with the inhomogeneous broadening.
KEYWORDS: System on a chip, Absorption, Solar cells, Crystals, Dye sensitized solar cells, Photovoltaics, Semiconductors, Chemical species, Cesium, Perovskite
Following pioneering works, the 3D hybrid lead-halide perovskites CH3NH3PbX3 (X=Cl, Br, I) have recently been shown to drastically improve the efficiency of Dye Sensitized Solar Cells (DSSC). It is predicted to open “a new era and a new avenue of research and development for low-cost solar cells … likely to push the absolute power conversion efficiency toward that of CIGS (20%) and then toward and beyond that of crystalline silicon (25%)” (Snaith, H. J. Phys Chem. Lett. 4, 3623-3630 (2013).). Here, we investigate theoretically the crystalline phases of one of the hybrids relevant for photovoltaic applications, namely CH3NH3PbCl3. Critical electronic states and optical absorption are thoroughly investigated both in the low and high temperature phases. Our findings reveal the dramatic effect of spin orbit coupling on their multiple band gaps. Their physical properties are compared to those of conventional semiconductors, evidencing inversion of band edge states.
The near-threshold dynamics of a QD and a commercial QW laser are investigated both experimentally and theoretically. Below threshold, the resonance frequency and damping factor of the QD laser exhibit a different behaviour as compared to the QW counterpart. In the near-threshold regime, the intra-dot carrier relaxation is predicted from an empirical pairstates model to have a strong impact on the QD laser’s modulation dynamics. The widespread of experimental values for the damping factor reported in the literature for QD lasers is a further indication that this empirical approach is pushed to the limits in this situation. More accurate microscopic modelling should rely on a separation of electron and hole dynamics.
The frequency chirp characteristics of an optically injection-locked quantum cascade laser are theoretically investigated. The key parameter chirp-to-power ratio (CPR) is analytically derived from a full rate equation model. The CPR value can be efficiently reduced by increasing optical injection strength, especially at modulation frequencies less than 10 GHz. In contrast to interband lasers, both positive and negative frequency detuning increase the CPR. Since the frequency detuning is also predicted to enhance the intensity modulation response, a trade-off is required in the optical injection to simultaneously obtain a large modulation bandwidth and low frequency chirp.
Nondegenerate four-wave mixing (NDFWM) in semiconductor gain media is a promising source for wavelength conversion in the wavelength division multiplexed (WDM) systems and for fiber dispersion compensation in long distance fiber links. In contrast to bulk and quantum well (QW) semiconductors, the quantum dot (QD) gain medium is favorable for enhancing the performance of the FWM because of the wide gain spectrum, large nonlinear effect as well as ultrafast carrier dynamics. Especially, the destructive interference can be eliminated due to the reduced linewidth enhancement factor (LEF) for obtaining high efficiency in the wavelength up-conversion. This work reports the NDFWM generation in a dual-mode injection-locked QD Fabry-Perot (FP) laser. The device has a wide gain spectrum with a full width at half maximum of 81 nm, and a peak net modal gain of 14.4 cm-1. The laser exhibits two lasing peaks induced by Rabi oscillation, which provides the possibility for efficient FWM generation. Employing the dual-mode injection-locking scheme, an efficient NDFWM is achieved up to a detuning range of 1.7 THz with a weak injection ratio of 0.44. The highest measured values for both the normalized conversion efficiency (NCE) and the side-mode suppression ratio (SMSR) with respect to the converted signal respectively are -17 dB and 20.3 dB at the detuning 110 GHz.
Transparent conducting metal oxides (TCO) are unusual semiconducting materials displaying transparency to visible light. TCO materials are used for electrostatic shielding, antistatic screens, transparent heating devices, solar cells and even organic light emitting diodes. However, most TCOs are n-type, while p-type TCOs are scarce. SrCu2O2 is a leading candidate as a p-type transparent conductive oxide. In this paper, we report theoretical calculations and experimental studies on the vibrational, optical and microstructural properties of both bulk and thin films of polycrystalline undoped SrCu2O2 obtained by pulsed laser deposition (PLD). Barium doping of the SrCu2O2 by substitution of Sr atoms is also reported. The simulated crystal structures of both SrCu2O2 and BaCu2O2 materials, obtained through a state-of-the-art implementation of the Density functional theory, are compared with experimental X-ray diffraction data of undoped and Ba-doped SrCu2O2 bulk materials. Raman spectra of both SCO and BCO materials are simulated from the derivatives of the dielectric susceptibility and a symmetry analysis of the optical phonon eigenvectors at the Brillouin zone center is proposed. Good agreement with Raman scattering experimental results is demonstrated.
Taking into account the carrier dynamics in the wetting layer, excited state and the ground state, the intensity modulation properties of an injection-locked quantum dot laser are studied theoretically through a semi-analytical approach. It is demonstrated that both high carrier capture and relaxation rates enhance the modulation bandwidth as well as the resonance-peak amplitude. Moreover, the pre-resonance dip arising under positive detuning can be eliminated as well, which is beneficial for further bandwidth enhancement. It is also found that a large capture time reduces both the resonance frequency and the damping factor while both are increased by a large relaxation time.
The intensity modulation (IM) property of an optical injection-locked quantum cascade (QC) laser is theoretically investigated via a three-level rate equation model. The locking regime is obtained based on the local bifurcation theory. It is shown that the injection-locked QC laser exhibits a rather flat modulation response at zero detuning, whose bandwidth increases with the injection level. In contrast to interband lasers, both positive and negative detunings enhance the modulation bandwidth. Besides, a large linewidth enhancement factor (LEF) can increase the peak amplitude in the response. Moreover, it is found that no frequency dip occurs in the IM response of injection-locked QC lasers.
Lattice-matched GaP-based nanostructures grown on silicon substrates is a highly rewarded route for coherent
integration of photonics and high-efficiency photovoltaic devices onto silicon substrates. We report on the structural and
optical properties of selected MBE-grown nanostructures on both GaP substrates and GaP/Si pseudo-substrates. As a
first stumbling block, the GaP/Si interface growth has been optimised thanks to a complementary set of thorough
structural analyses. Photoluminescence and time-resolved photoluminescence studies of self-assembled (In,Ga)As
quantum dots grown on GaP substrate demonstrate a proximity of two different types of optical transitions interpreted as
a competition between conduction band states in X and Γ valleys. Structural properties and optical studies of
GaAsP(N)/GaP(N) quantum wells coherently grown on GaP substrates and GaP/Si pseudo substrates are reported. Our
results are found to be suitable for light emission applications in the datacom segment. Then, possible routes are drawn
for larger wavelengths applications, in order to address the chip-to-chip and within-a-chip optical interconnects and the
optical telecom segments. Finally, results on GaAsPN/GaP heterostructures and diodes, suitable for PV applications are
reported.
The three-dimensional confinement of electrons and holes in the semiconductor quantum dot (QD) structure profoundly
changes its density of states compared to the bulk semiconductor or the thin-film quantum well (QW) structure. The aim
of this paper is to theoretically investigate the microwave properties of InAs/InP(311B) QD lasers. A new expression of
the modulation transfer function is derived for the analysis of QD laser modulation properties based on a set of four rate
equations. Analytical calculations point out that carrier escape from ground state (GS) to excited state (ES) induces a
non-zero resonance frequency at low bias powers. Calculations also show that the carrier escape leads to a larger
damping factor offset as compared to conventional QW lasers. These results are of prime importance for a better
understanding of the carrier dynamics in QD lasers as well as for further optimization of low cost sources for optical
telecommunications.
T. Nguyen Thanh, C. Robert, C. Cornet, W. Guo, A. Letoublon, M. Perrin, N. Bertru, J. Even, N. Chevalier, H. Folliot, S. Loualiche, A. Ponchet, G. Elias, J. S. Micha, O. Durand, A. Le Corre
Selected results obtained in the framework of MBE grown nanostructure for photonics on silicon are repsented in this
paper. We present first a comprehensive study of GaAsPN/GaPN quantum wells (QWs) grown onto GaP substrates, in
the light of a comparison with their N-free GaAsP/GaP QWs counterpart system. High density of small InGaAs/GaP
Quantum Dots are presented next with their PL properties. Finally, RT photoluminescence properties of GaAsPN/GaPN
QWs onto Si substrate are presented and discussed in term of carrier injection efficiency. However, for future
development, optical properties of the active area must be improved and are tightly bound to the structural perfection of
the GaP/Si template layer. To address this point, structural analyses including X-Ray Diffraction (lab setup and
synchrotron) and Transmission Electron Microscopy have been performed, with a particular care for typical III-V/Si
defect characterisation. First results of Si buffer layer growth are also presented as a perspective for future low defect
MBE grown GaP/Si template layers.
Simultaneous absorption of two photons has gained increasing attention over recent years as it opens the way for
improved and novel technological capabilities. In the search for adequate materials that combine large two-photon
absorption (TPA) responses and attributes suitable for specific applications, the multibranch strategy has proved to be
efficient. Such molecular engineering effort, based on the gathering of several molecular units, has benefited from
various theoretical approaches. Among those, the Frenkel exciton model has been shown to often provide a valuable
qualitative tool to connect the optical properties of a multibranched chromophore to those of its monomeric counterpart.
In addition, recent extensions of time-dependent density functional theory (TD-DFT) based on hybrid functionals have
shown excellent performance for the determination of nonlinear optical (NLO) responses of conjugated organic
chromophores and various substituted branched structures. In this paper, we use these theoretical approaches to
investigate the one- and two-photon properties of triazole-based chromophores. In fact, experimental data were shown to
reveal quite different behaviors as compared to related quadrupolar and octupolar compounds. Our theoretical findings
allow elucidating these differences and contribute to the general understanding of structure-property relations. This work
opens new perspectives towards synergic TPA architectures.
Thanks to optimized growth techniques, a high density of uniformly sized InAs quantum dots (QD) can be grown on
InP(113)B substrates. Low threshold currents obtained at 1.54 μm for broad area lasers are promising for the future. This
paper is a review of the recent progress toward the understanding of electronic properties, carrier dynamics and device
modelling in this system, taking into account materials and nanostructures properties. A first complete analysis of the
carrier dynamics is done by combining time-resolved photoluminescence experiments and a dynamic three-level model,
for the QD ground state (GS), the QD excited state (ES) and the wetting layer/barrier (WL). Auger coefficients for the
intradot assisted relaxation are determined. GS saturation is also introduced. The observed double laser emission for a
particular cavity length is explained by adding photon populations in the cavity with ES and GS resonant energies. Direct
carrier injection from the WL to the GS related to the weak carrier confinement in the QD is evidenced. In a final step,
this model is extended to QD GS and ES inhomogeneous broadening by adding multipopulation rate equations
(MPREM). The model is now able to reproduce the spectral behavior in InAs-InP QD lasers. The almost continuous
transition from the GS to the ES as a function of cavity length is then attributed to the large QD GS inhomogeneous
broadening comparable to the GS-ES lasing energy difference. Gain compression and Auger effects on the GS transition
are also be discussed.
InAs nanostructures formed on InP substrates allow the realization of devices working in telecommunication wavelength range between 1.4 and 1.65 μm. However due to the low lattice mismatch existing between InAs and InP, the self assembling process in InP is more complex than on GaAs substrates. First high density quantum wires obtained on InP(001) have been integrated in laser. Lasers emitting at room
temperature have been achieved. For an infinite length cavity, a threshold current density per QD plane as low as 45 A/cm2 is deduced. This result compares favourably with those obtained on quantum wells lasers. However, the stability of the threshold current with temperature, predicted for quantum dots laser is not
observed. Thus, growth on non standard substrates such as miscut substrates or high index substrates have been investigated in order to achieve QDs on InP. On (113) B substrates, quantum dots in high density and with size comparable with those achieved on GaAs(001) have been obtained. Lasers with record threshold current have been obtained. However the modulation properties of the laser are not as good as predicted for ideal quantum dots lasers. Finally we present the attempts to extend the QD emission wavelength in the 2-3
μm region.
Quantum dot (QD) lasers exhibit many useful properties such as low threshold current, temperature and feedback
insensitivity, chirpless behavior, and low linewidth enhancement factor. The aim of this paper is to investigate the lasing
spectra behaviour of InAs/InP(311B) QD lasers. In order to reach the standards of long-haul transmissions, 1.55μm
InAs QD lasers grown on InP substrate have been developed. More particularly, it has been demonstrated that the use of
the specific InP(113)B substrate orientation when combined with optimized growth techniques allows the growth of very
small (4 nm high) and dense (up to 1011cm-2) QD structures. Consequently, a model based on the multi-population rate
equations (MPRE) taking into account many cavity longitudinal modes for the calculation of the entire emission
spectrum has been developed. In order to include the inhomogeneous gain broadening of the QD ensemble, various dot
populations, each characterized by a ground state (GS) and an excited state (ES) average energy level have been
considered. It will be shown that the numerical results are in good agreement with the experimental ones, both for the
case of the double laser emission and for the effects of the homogeneous broadening on the lasing spectra. This
numerical investigation based on carrier dynamics is of prime importance for the optimization of low cost sources for
optical telecommunications as well as for a further improvement of QD laser performances at 1.55-μm on InP substrate,
as already demonstrated for InAs-GaAs QD lasers emitting at 1.3-μm.
The quantum dots have added great benefits to the photonic activity, among them the decoupling between the lattice parameter of the substrate and the dot has opened the way to enlarge the spectral windows which can be accessible on different substrates. For example on a GaAs substrate a long wavelength laser emission of 1.46 μm
has been demonstrated at room temperature. The specific properties like: large material gain, large spectral
bandwidth, high speed carrier dynamics, have improved device performances. The minimum threshold current
densities of laser devices, the large spectral bandwidth of semiconductor optical amplifiers and the very high
repetition rate and very short pulse width on mode locked lasers are other benefits.
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