Bragg Microcavities Research Articles

High sensitivity sensor based on circular Bragg micro-cavities

High sensitivity sensor based on circular Bragg micro-cavities

Progresses in III‐nitride distributed Bragg reflectors and microcavities using AlInN/GaN materials

AbstractWe propose to use lattice‐matched AlInN/GaN to replace the Al(Ga)N/GaN material system for III‐nitride Bragg reflectors, despite the poor material quality of AlInN reported until very recently. We report an improvement of AlInN material that allowed for successful fabrication of a microcavity light emitting diode, a distributed Bragg reflector with 99.4% reflectivity and microcavities with a quality factor over 800. These results establish state‐of‐the‐art values for III‐nitrides, and announce the future importance of AlInN in GaN‐based optoelectronics. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Planar silicon-based light polarizers

Silicon-based thin-film polarizers operating in the visible and near-infraed spectral range are fabricated by electrochemical etching of bulk silicon wafers. Anisotropically etched (110) porous silicon layers exhibit a strong in-plane anisotropy of the refractive index. Stackes of alternating layers with different mean refractive indices and thicknesses act as dichroic Bragg reflectors or microcavities, respectively. Both structures have two distinct reflection and transmission bands depending on the polarization of the incident linearly polarized light. Planar polarizers are realized through the combination, in one structure, of a dichroic reflector with either a second reflector or a microcavity with different spectral responses.

RBS studies of AlGaN/AlN Bragg reflectors

In this paper, the RBS phenomenon is described and experimental results concerning Bragg reflectors and microcavities grown on silicon substrates by molecular beam epitaxy are presented. This spectroscopy is not sensitive to (i) the lateral fluctuation of the alloy composition (the analyzed surface is about 1 mm(2)), (ii) to the residual strain of the layer or to (iii) the internal electric field. The measured thicknesses and compositions of the layers are very close to the nominal values. The Al concentration have been confirmed by low temperature photoluminescence experiments and the thicknesses by scanning electron microscopy studies. The straggling effect has been highlighted and plotted as function of the penetration depth of the particles.

Sol–gel fabrication of thick multilayers applied to Bragg reflectors and microcavities

We discuss attractive potentialities of the sol–gel process applied to planar microcavities with distributed Bragg reflectors (DBRs). This method is well known for its good flexibility and the optical quality of the thin films obtained. The DBRs are composed of alternated TiO 2 and SiO 2 thin films. One of the main problems of the sol–gel process is the stresses induced during the layers heat treatment leading to defects and cracks in the films. The study of these stresses shows that with the appropriate annealing temperature and duration of the firing process, the stress in the SiO 2 layers partially compensates the stress in the TiO 2 layers. DBRs and microcavities formed by 60 stacked layers have been elaborated in these conditions. The reflectivity of such sol–gel DBRs reaches 99.7%. The sol–gel DBRs are used to fabricate microcavities containing Eu 3+ rare earth ions with a quality factor of approximately 1000.

Organometallic chemical vapor deposition of V-groove InGaAs/GaAs quantum wires incorporated in planar Bragg microcavities

We report the fabrication and the optical properties of dense arrays of strained InGaAs/GaAs V-groove quantum wires (QWRs) embedded in wavelength size planar Bragg microcavities, made using a two-step organometallic chemical vapor deposition (OMCVD). Growth front evolution and top surface morphology of GaAs on the corrugated substrate were investigated as a function of the growth temperature (550–625°C) and the pitch of the V-groove grating (3–0.25 μm). Based on these studies, a growth temperature of 550°C and a grating pitch of 0.25 μm were selected to achieve sizes compatible with simultaneous quantum confinement for electron (≈10 nm wide wires) and photon (≈0.25 μm thick cavities) states. Reference arrays of uniform, nanometer-size, crescent-shaped, InGaAs QWRs with densities up to 4QWRs/μm were realized, exhibiting a narrow (8 meV) and intense emission from one-dimensional excitonic states at low temperature. Similar QWRs were then successfully embedded in planar microcavities, showing brighter (×50) emission with a strongly reduced linewidth (1 meV) due to resonant coupling between the wire emission and the microcavity modes.

Improvement of the luminescence in p-type as-prepared or dye impregnated porous silicon microcavities

We have realized distributed Bragg reflectors and microcavities with a remarkable optical quality ( R max.=99.5% at 850 nm, FWHM=5 nm at 772 nm) with low doped p-type silicon. This is due to a strong decrease of the porous Si/bulk Si interface roughness that was obtained by low-temperature anodization. The properties of porous silicon microcavities are investigated by photoluminescence and reflection measurements. We also have filled porous silicon with Rhodamine 800 dye. The spontaneous emission spectrum of the optically excited Rhodamine 800 is drastically modified by microcavity effect: the peak emission intensity is increased, the line width is narrowed. The results demonstrate that using all porous silicon or dye-filled microcavities provides new possibilities to improve the properties of photonic devices.

Enhancement of spontaneous emission rates by three-dimensional photon confinement in Bragg microcavities

Three-dimensionally confined Bragg microcavities exhibiting several fully quantized photon modes have been investigated by time-resolved photoluminescence spectroscopy. A strong decrease of the exciton lifetime with decreasing lateral dimension is observed and shown to be mainly due to coupling of the long-lived excitons with short-lived photon modes. We observe similar decay times of all photon modes for a fixed structure size which amount to approximately half of the corresponding exciton lifetimes. This behavior is explained by incoherent Auger-type scattering processes populating the photon modes on the low-energy side of the exciton line.

Fabrication of InP/air-gap distributed Bragg reflectors and micro-cavities

High reflective Bragg reflectors based on suspended InP-layers were fabricated by selective wet etching. Areas as large as 15 × 20 μm 2 could be realized. Two three-period mirrors were employed in a cavity with a 1.3 μm GaInAsP active layer. The spectral reflectivity of the structure exhibits a Fabry Perot resonance at 1.32 μm. When excited with a Nd-YAG laser, the structure generates a narrow emission at the same wavelength and a linewith of ⩽2.5 nm.

Elaboration and Light Emission Properties of Low Doped p-Type Porous Silicon Microcavities

AbstractWe account for the elaboration of Bragg reflectors and microcavities based on efficiently luminescent porous silicon. A characterisation of very thin porous silicon layers obtained with current densities of formation varying from 1.5 mA to 300 mA is presented. The resulting refractive index variation (typically from 1.37 to 1.86 at 700 nm) enables the elaboration of high quality Bragg reflectors and Fabry-Perot filters from the yellow to the near infrared. Although low doped p-type porous silicon develops rougher interfaces than highly doped p-type porous silicon, its better luminescence efficiency has enabled us to elaborate microcavities with a strong emission in a narrow band.