Suppression of cross-hatched polariton disorder in GaAs/AlAs microcavities by strain compensation
Wolfgang Langbein2012, Applied Physics Letters
Sign up for access to the world's latest research
checkGet notified about relevant papers
checkSave papers to use in your research
checkJoin the discussion with peers
checkTrack your impact
Abstract
GaN hybrid microcavities in the strong coupling regime grown by metal-organic chemical vapor deposition on sapphire substrates
Related papers
Polariton states bound to defects in GaAs/AlAs planar microcavities
Physical Review B, 2012
We report on polariton states bound to defects in planar GaAs/AlAs microcavities grown by molecular beam epitaxy. The defect types relevant for the spatial polariton dynamics in these structures are cross-hatch misfit dislocations, and point-like defects extended over several micrometers. We attribute the latter defects to Ga droplets emitted occasionally by the Ga cell during the growth. These defects, also known as oval defects, result in a dome-like local modulation of surface, which is translated into the cavity structure and leads to a lateral modulation of the cavity polariton energy of up to 15 meV. The resulting spatially localized potential landscape for the in-plane polariton motion creates a series of bound states. These states were characterized by spectrally resolved transmission imaging in real and reciprocal space, and reveal the spatial potential created by the defects. Interestingly, the defect states exhibit long lifetimes in the 10 ps range, which we attribute to a spatially smooth confinement potential.
Comparison of strong coupling regimes in bulk GaAs, GaN, and ZnO semiconductor microcavities
Physical Review B, 2008
Broadening of upper polariton branch in GaAs, GaN, and ZnO semiconductor microcavities
Applied Physics B, 2011
The well-distinguished lower polariton branches (LPBs) and upper polariton branches (UPBs) are characteristics of strong coupling in semiconductor microcavities (MCs). In practice, however, the UPBs are often broadening especially in wide-bandgap material MCs. We present in detail the possible physical mechanisms for the broadening of UPBs for different designs of MCs by numerical simulations based on GaAs, GaN and ZnO materials. The calculated results show that the UPBs of the GaN-and ZnObased MCs will become indistinct when the thickness of optical cavity is larger than λ and 0.25λ, respectively, mainly attributed to the larger product of the absorption coefficient and the active layer thickness. In wide-bandgap materials, it would be relatively easier to observe the UPB in the case of negative exciton-cavity mode detuning due to the excitonlike UPB and lower absorption of scattering states. In addition, the inhomogeneous broadening would be an important factor causing the invisible UPB in wide-bandgap semiconductor MCs. We demonstrate that in multiple quantum well embedded ZnO-based MCs, the UPB could be well defined due to the large 2D exciton binding energy and the small product of absorption coefficient and active layer thickness. These results show that the UPBs can be properly defined in wide-bandgap semiconductor MCs by appropriate design of the MC structures.
Strong Light-Matter Coupling in GaN-Based Microcavities Grown on Silicon Substrates
MRS Proceedings, 2008
We present an overview of our work concerning the fabrication of GaN-based microcavities grown on silicon substrates dedicated to the observation of the strong light-matter coupling regime. In the view of recent promising results in the field, prospects regarding the improvement of heterostructures in order to observe room temperature polariton lasing from a GaN-based microcavity grown on a silicon substrate will be discussed.
Structure and zero-dimensional polariton spectrum of natural defects in GaAs/AlAs microcavities
Physical Review B, 2012
We present a correlative study of structural and optical properties of natural defects in planar semiconductor microcavities grown by molecular beam epitaxy, which are showing a localized polariton spectrum as reported in Zajac et al., Phys. Rev. B 85, 165309 (2012). The three-dimensional spatial structure of the defects was studied using combined focussed ion beam (FIB) and scanning electron microscopy (SEM). We find that the defects originate from a local increase of a GaAs layer thickness. Modulation heights of up to 140 nm for oval defects and 90 nm for round defects are found, while the lateral extension is about 2µm for oval and 4µm for round defects. The GaAs thickness increase is attributed to Ga droplets deposited during growth due to Ga cell spitting. Following the droplet deposition, the thickness modulation expands laterally while reducing its height, yielding oval to round mounds of the interfaces and the surface. With increasing growth temperature, the ellipticity of the mounds is decreasing and their size is increasing. This suggests that the expansion is related to the surface mobility of Ga, which with increasing temperature is increasing and reducing its anisotropy between the [110] and [110] crystallographic directions. Comprehensive data consisting of surface profiles of defects measured using differential interference contrast (DIC) microscopy, volume information obtained using FIB/SEM, and characterization of the resulting confined polariton spectrum are presented.
GaN/AlGaN microcavities for enhancement of non linear optical effects
2011
We present a study on the design, growth and optical characterization of a GaN/AlGaN microcavity for the enhancement of second order non linear effects. The proposed system exploits the high second order nonlinear optical response of GaN due to the non centrosymmetric crystalline structure of this material. It consists of a GaN cavity embedded between two GaN/AlGaN Distributed Bragg Reflectors designed for a reference mode coincident with a second harmonic field generated in the near UV region (~ 400 nm). Critical issues for this target are the crystalline quality of the material, together with sharp and abrupt interfaces among the multi-stacked layers. A detailed investigation on the growth evolution of GaN and AlGaN epilayers in such a configuration is reported, with the aim to obtain high quality factor in the desiderated spectral range. Non linear second harmonic generation experiments have been performed and the results were compared with bulk GaN sample, highlighting the effect of the microcavity on the non linear optical response of this material.
Strong exciton-photon coupling in hybrid InGaN-based microcavities on GaN substrates
Gallium Nitride Materials and Devices X, 2015
A 5λ-thick hybrid semiconductor/dielectric GaN-based microcavity grown by metal-organic chemical vapor deposition on a c-plane bulk GaN substrate was investigated using angle-resolved photoluminescence and angle-resolved cathodoluminescence techniques at room and low temperature (5.8 K), respectively. The cavity structure consisted of an InGaN multiple quantum well active region emitting at 400 nm and sandwiched between 29.5 pair bottom semiconductor AlN/GaN and 13.5 pair top dielectric SiO 2 /SiN x distributed Bragg reflectors. The cavity supported strong exciton-photon coupling with a record 75 meV vacuum Rabi splitting energy at 5.8 K. The measured room temperature Rabi splitting energy of 45 meV is still close to the highest Rabi splitting energies reported in literature confirming that the strong coupling regime still persists at room temperature.
Dynamic polariton condensation in a single GaN nanowire-dielectric microcavity
Physical Review B, 2012
We have experimentally investigated the dynamic polariton condensation behavior in a single GaN nanowire strongly coupled to a dielectric microcavity under non-resonant optical excitation. Both time-integrated and time-resolved polariton luminescence measurements have been made in the temperature range of 25 to 100K (corresponding to exciton-cavity photon detuning of-3.0 to +4.2 meV). Polariton lasing is observed in the entire temperature range, with the lowest threshold energy of 57 nJ/cm 2 measured at 50K (δ =-1.3 meV). All the measurements indicate that at the lower temperatures, the degenerate polariton condensate is not in thermal equilibrium with the phonon bath. At 85 and 100K (δ = +2.3 and 4.2 meV) the system attains a state close to thermal equilibrium via dynamic Bose condensation. The best results are obtained at T latt = 85K, for which T LP = 88.8K, and this is the highest temperature recorded for an equilibrium phase transition in exciton-polariton condensates.
GaN microcavities and Bragg reflectors: giant exciton–light coupling
Materials Science and Engineering: B, 1999
Numerical simulation of light reflection from a u/2 GaN microcavity with Ga 0.8 Al 0.2 N/Ga 0.5 Al 0.5 N Bragg mirrors grown on the A-surface of Al 2 O 3 revealed a Rabi-splitting of the order of 50 meV and remarkable optical anisotropy. In a separate Bragg mirror, the exciton interference results in a 95% modulation of reflection spectra. These effects originate from the giant exciton oscillator strength in GaN and a pronounced uniaxial strain in the structure.
Dual-polarity GaN micropillars grown by metalorganic vapour phase epitaxy : Cross correlation between structural and optical properties
Self-assembled catalyst-free GaN micropillars grown on (0001) sapphire substrates by metal organic vapor phase epitaxy are investigated. Transmission electron microscopy, as well as KOH etching, shows the systematic presence of two domains of opposite polarity within each single micropillar. The analysis of the initial growth stages indicates that such double polarity originates at the micropillar/substrate interface, i.e., during the micropillar nucleation, and it propagates along the micropillar. Furthermore, dislocations are also generated at the wire/substrate interface, but bend after several hundreds of nanometers. This leads to micropillars several tens of micrometers in length that are dislocation-free. Spatially resolved cathodoluminescence and microphotoluminescence show large differences in the optical properties of each polarity domain, suggesting unequal impurity/dopant/vacancy incorporation depending on the polarity.
Related topics
Cited by
Ghost Branch Photoluminescence From a Polariton Fluid Under Nonresonant Excitation
Physical Review Letters, 2015
An expanding polariton condensate is investigated under pulsed nonresonant excitation with a small laser pump spot. Far above the condensation threshold we observe a pronounced increase in the dispersion curvature with a subsequent linearization of the spectrum and strong luminescence from a ghost branch orthogonally polarized with respect to the linearly polarized condensate emission. The presence of the ghost branch has been confirmed in time-resolved measurements. The dissipative and nonequilibrium effects in the photoluminescence of polariton condensates and their excitations are discussed.
Structure and zero-dimensional polariton spectrum of natural defects in GaAs/AlAs microcavities
Physical Review B, 2012
We present a correlative study of structural and optical properties of natural defects in planar semiconductor microcavities grown by molecular beam epitaxy, which are showing a localized polariton spectrum as reported in Zajac et al., Phys. Rev. B 85, 165309 (2012). The three-dimensional spatial structure of the defects was studied using combined focussed ion beam (FIB) and scanning electron microscopy (SEM). We find that the defects originate from a local increase of a GaAs layer thickness. Modulation heights of up to 140 nm for oval defects and 90 nm for round defects are found, while the lateral extension is about 2µm for oval and 4µm for round defects. The GaAs thickness increase is attributed to Ga droplets deposited during growth due to Ga cell spitting. Following the droplet deposition, the thickness modulation expands laterally while reducing its height, yielding oval to round mounds of the interfaces and the surface. With increasing growth temperature, the ellipticity of the mounds is decreasing and their size is increasing. This suggests that the expansion is related to the surface mobility of Ga, which with increasing temperature is increasing and reducing its anisotropy between the [110] and [110] crystallographic directions. Comprehensive data consisting of surface profiles of defects measured using differential interference contrast (DIC) microscopy, volume information obtained using FIB/SEM, and characterization of the resulting confined polariton spectrum are presented.
Geometric frustration in polygons of polariton condensates creating vortices of varying topological charge
Nature Communications, 2021
Vorticity is a key ingredient to a broad variety of fluid phenomena, and its quantised version is considered to be the hallmark of superfluidity. Circulating flows that correspond to vortices of a large topological charge, termed giant vortices, are notoriously difficult to realise and even when externally imprinted, they are unstable, breaking into many vortices of a single charge. In spite of many theoretical proposals on the formation and stabilisation of giant vortices in ultra-cold atomic Bose-Einstein condensates and other superfluid systems, their experimental realisation remains elusive. Polariton condensates stand out from other superfluid systems due to their particularly strong interparticle interactions combined with their non-equilibrium nature, and as such provide an alternative testbed for the study of vortices. Here, we non-resonantly excite an odd number of polariton condensates at the vertices of a regular polygon and we observe the formation of a stable discrete v...
Polariton condensation in a strain-compensated planar microcavity with InGaAs quantum wells
Applied Physics Letters, 2014
The investigation of intrinsic interactions in polariton condensates is currently limited by the photonic disorder of semiconductor microcavity structures. Here, we use a strain compensated planar GaAs/AlAs0.98P0.02 microcavity with embedded InGaAs quantum wells having a reduced cross-hatch disorder to overcome this issue. Using real and reciprocal space spectroscopic imaging under non-resonant optical excitation, we observe polariton condensation and a second threshold marking the onset of photon lasing, i.e., the transition from the strong to the weak-coupling regime. Condensation in a structure with suppressed photonic disorder is a necessary step towards the implementation of periodic lattices of interacting condensates, providing a platform for on chip quantum simulations.
Related papers
From evidence of strong light–matter coupling to polariton emission in GaN microcavities
physica status solidi (b), 2007
We present both experimental and theoretical results which outline our development of the molecular beam epitaxy of GaN microcavities on (111) silicon. In particular we show that although in this material system the strong-light matter coupling regime can be observed at 300 K even with relatively low quality factor structures (Q = 60) in reflectivity measurements, it is necessary to increase the Q-factor by at least a factor of two to observe strong coupling in the emission. For an optimized microcavity structure (Q = 160), polaritonic emission is observed at 300 K, with the origin of the broadened luminescence features confirmed by co-incident reflectivity measurements.
Polariton condensation phase diagram in wide-band-gap planar microcavities GaN versus ZnO
The polariton condensation phase diagram is compared in GaN and ZnO microcavities grown on mesa-patterned silicon substrate. Owing to a common platform, these microcavities share similar photonic properties with large quality factors and low photonic disorder, which makes it possible to determine the optimal spot diameter and to realize a thorough phase diagram study. Both systems have been investigated under the same experimental conditions. The experimental results and the subsequent analysis reveal clearly that longitudinal optical phonons have no influence in the thermodynamic region of the condensation phase diagram, while they allow a strong (slight) decrease of the polariton lasing threshold in the trade-off zone (kinetic region). Phase diagrams are compared with numerical simulations using Boltzmann equations, and are in satisfactory agreement. A lower polariton lasing threshold has been measured at low temperature in the ZnO microcavity, as is expected due to a larger Rabi splitting. This study highlights polariton relaxation mechanisms and their importance in polariton lasing.
Tailoring the light-matter coupling in anisotropic microcavities: Redistribution of oscillator strength in strainedm-plane GaN/AlGaN quantum wells
Physical Review B, 2011
We present a comprehensive study of the anisotropic optical properties of nonpolar GaN/AlGaN multiple quantum wells intentionally designed to act as an active region of a planar microcavity operating in the strongcoupling regime. The strain induced by the underlying AlGaN-based Bragg reflector leads to a redistribution of exciton oscillator strength as revealed by photoluminescence and reflectivity measurements. Complementary k • p calculations show an excellent agreement with experiments and emphasize the opportunity to tune the nature of the light-matter coupling in a microcavity by means of strain engineering. Finally, the validity of the developed model is proven by angle-resolved photoluminescence studies carried out on the complete microcavity structure. The recorded eigenmode spectra reveal the coexistence of the weak-and the strong-coupling regime along the two orthogonal polarization planes.
All-dielectric GaN microcavity: Strong coupling and lasing at room temperature
Applied Physics Letters, 2013
The strong light-matter coupling regime and lasing in a GaN microcavity fabricated by incorporating a high optical quality GaN membrane inside an all-dielectric mirror cavity is demonstrated at room temperature. A nonlinear increase of the emission and line narrowing marks the onset of polariton lasing regime with significantly reduced threshold compared with previous reports for bulk GaN microcavity. This combination of low lasing thresholds and ease of fabrication allows incorporation of quantum wells and electrical contacts into the active region, paving the way for electrically driven room temperature polariton laser devices.
Strong light-matter coupling in bulk GaN-microcavities with double dielectric mirrors fabricated by two different methods
Journal of Applied Physics, 2010
Two routes for the fabrication of bulk GaN microcavities embedded between two dielectric mirrors are described, and the optical properties of the microcavities thus obtained are compared. In both cases, the GaN active layer is grown by molecular beam epitaxy on ͑111͒ Si, allowing use of selective etching to remove the substrate. In the first case, a three period Al 0.2 Ga 0.8 N / AlN Bragg mirror followed by a / 2 GaN cavity are grown directly on the Si. In the second case, a crack-free 2 m thick GaN layer is grown, and progressively thinned to a final thickness of . Both devices work in the strong coupling regime at low temperature, as evidenced by angle-dependent reflectivity or transmission experiments. However, strong light-matter coupling in emission at room temperature is observed only for the second one. This is related to the poor optoelectronic quality of the active layer of the first device, due to its growth only 250 nm above the Si substrate and its related high defect density. The reflectivity spectra of the microcavities are well accounted for by using transfer matrix calculations.
Modelling and Spectroscopy of GaN Microcavities
physica status solidi (a), 2002
Two GaN microcavities have been grown on Si(111) substrates by molecular beam epitaxy. The first one is constituted of a (l/2) GaN cavity with 12 (l/4) AlN/Al 0.20 Ga 0.80 N bilayers as the top mirror, the Si substrate acting as the bottom mirror. The second one is a (2l) GaN cavity sandwiched between 13 and 15 AlN/Al 0.20 Ga 0.80 N periods, respectively, for the top and bottom mirrors. Reflectivity and photoluminescence experiments were carried out under normal incidence at low temperature (T ¼ 5 K). The reflectivity spectra reveal a cavity mode whose linewidth is about 30 meV. Our experiments demonstrate that the cavity mode controls the GaN emission. The modelling of the luminescence spectra as a function of the cavity resonance energy allows to estimate the spectral broadening of the GaN emission line to about 50 meV; this value seems to be responsible for the non-observation of the strong coupling.
Strong light-matter coupling in ultrathin double dielectric mirror GaN microcavities
Applied Physics Letters, 2008
Strong light-matter coupling is demonstrated at low temperature in an ultrathin GaN microcavity fabricated using two silica/zirconia Bragg mirrors, in addition to a three-period epitaxial ͑Al,Ga͒N mirror serving as an etch stop and assuring good quality of the overgrown GaN. The / 2 cavity is grown by molecular beam epitaxy on a Si substrate. Analysis of angle-resolved data reveal key features of the strong coupling regime in both reflectivity and transmission spectra at 5 K: anticrossing with a normal mode splitting of 43Ϯ 2 meV and 56Ϯ 2 meV for reflectivity and transmission, respectively, and narrowing of the lower polariton linewidth near resonance.
GaN microwires as optical microcavities: whispering gallery modes Vs Fabry-Perot modes
Optics Express, 2012
GaN microwires grown by metalorganic vapour phase epitaxy and with radii typically on the order of 1-5 micrometers exhibit a number of resonances in their photoluminescence spectra. These resonances include whispering gallery modes and transverse Fabry-Perot modes. A detailed spectroscopic study by polarization-resolved microphotoluminescence, in combination with electron microscopy images, has enabled to differentiate both kinds of modes and determined their main spectral properties. Finally, the dispersion of the ordinary and extraordinary refractive indices of strainfree GaN in the visible-UV range have been obtained thanks to the numerical simulation of the observed modes.
Room-temperature polariton lasers based on GaN microcavities
Applied Physics Letters, 2002
The critical temperature for Bose condensation of exciton polaritons in an AlGaN microcavity containing 9 GaN quantum wells is calculated to be T=460 K. We have modeled the kinetics of polaritons in such a microcavity device using the two-dimensional Boltzmann equation. Room-temperature lasing is found with a threshold as small as 100 mW. The kinetic blocking of polariton relaxation that prevents formation of the Bose-condensed phase of polaritons at low temperatures disappears at high temperatures, especially in n-doped samples. Thus, GaN microcavities are excellent candidates for realization of room-temperature polariton lasers.
Roles for aluminium indium nitride insertion layers in fabrication of GaN-based microcavities
physica status solidi (a), 2005
AlInN alloys achieve an in-plane lattice match to hexagonal GaN at an indium nitride mole fraction of ~18%. Meanwhile Al 0.82 In 0.18 N displays a refractive index contrast of ~7% with GaN at visible wavelengths. We illustrate the use of Al 0.82 In 0.18 N insertion layers to control layer thicknesses during homoepitaxial growth of GaN-based microcavities, using in situ optical reflectometry. The structures discussed are 3λ/2 microcavities incorporating distributed InGaN quantum wells tailored for emission at ~400 nm. As-grown samples have been characterised by techniques including cathodoluminescence spectroscopy. In addition to their role in growth monitoring, there are several post-growth processing steps in which Al 0.82 In 0.18 N insertion layers can assist microcavity fabrication. We focus here on a demonstration of the ~1 : 5 etch rate selectivity obtainable between Al 0.82 In 0.18 N and GaN in reactive ion etching.
Loading Preview
Sorry, preview is currently unavailable. You can download the paper by clicking the button above.