Top Mirror Research Articles

High-performance 1.55μm low-temperature-grown GaAs resonant-cavity-enhanced photodetector

A 1.55μm low-temperature-grown GaAs (LT-GaAs) photodetector with a resonant-cavityenhanced structure was designed and fabricated. A LT-GaAs layer grown at 200°C was used as the absorption layer. Twenty- and fifteen-pair GaAs∕AlAs-distributed Bragg reflectors were grown as the bottom and top mirrors. A responsivity of 7.1mA∕W with a full width at half maximum of 4nm was obtained at 1.61μm. The dark current densities are 1.28×10−7A∕cm2 at the bias of 0V and 3.5×10−5A∕cm2 at the reverse bias of 4.0V. The transient response measurement showed that the photocarrier lifetime in LT-GaAs is 220fs.

Design of a silicon resonant cavity enhanced photodetector based on the internal photoemission effect at 1.55 µm

In this paper, the design of a resonant cavity enhanced photodetector, working at 1.55 µm and based on silicon technology, is reported. The photon absorption is due to the internal photoemission effect over the Schottky barrier at the metal–silicon interface. The photodetector is composed of a silicon layer in between multiple layers of Si–SiO2, as a bottom mirror, and a thin Au film and dielectric coating, as a top mirror. In order to estimate the quantum efficiency, we take advantage of the analytical formulation of the internal photoemission effect (Fowler theory) and its extension for thin films, while for the optical analysis of the device, used to calculate mirror reflectivities and active layer absorptance, a numerical method based on the transfer matrix method has been implemented. Our numerical results prove a significant enhancement of the efficiency obtained at resonant wavelengths by a very thin absorbing layer.

Ultranarrow band and high-quantum-efficiency photoresponse of Ge-on-Si photodetectors using cascaded-cavity structure

A resonant cavity mirror structure is incorporated into the top mirror of Ge-on-Si resonant cavity enhanced photodetectors to obtain ultranarrow band and high-quantum-efficiency photoresponse at the same time, which takes advantage of the combined effect of the top resonant cavity mirror and the absorption resonant cavity. The proposed structure is simulated and optimized by matrix method, resulting in a 3dB linewidth of 0.4nm and quantum efficiency of 96.8%. In addition, different reflectance profiles of the proposed structure are also presented, which can be used for different specific requirements.

Microcavity effects on emissive color and electroluminescent performance in organic light-emitting diodes

Microcavity organic light-emitting diodes having a top metal mirror and a bottom dielectric mirror, which was distributed Bragg reflectors (DBR) fabricated by using TiO 2–SiO 2 alternative dielectric multilayer with a central stop-band and two sub-stop-bands, were fabricated. In the devices, the active layers consisted of a hole-transporting layer N, N′-di(naphthalene-l-yl)- N, N′-diphenylbenzidine (NPB) and an electron-transporting/emitting layer tris(8-hydroxy-quinoline) aluminum (Alq 3). The relationship of the electroluminescent (EL) spectrum and efficiency with the thickness of the active layer and metal layer was studied. It was found that the EL emissive color did not strongly depend on the thickness of the organic layer and metal layer, which was attributed to the excellent photon confinement role of the narrow stop-band of the used dielectric mirror. Thus, high efficiency microcavity organic light-emitting diodes were achieved, and the peak wavelength and color purity were not obviously changed, via optimizing the thickness of organic layer and metal electrode.

1.32 μ m InAs∕GaAs quantum-dot resonant-cavity light-emitting diodes grown by metalorganic chemical vapor deposition

The first demonstration of InAs∕GaAs quantum-dot (QD) resonant-cavity light-emitting diode (RCLED) operating at 1.32μm at room temperature is reported. A single-layer InAs QDs inserted in GaAs matrix as the active medium was grown by metalorganic chemical vapor deposition. The bottom and top mirrors of QD RCLEDs were fabricated by employing epitaxial AlGaAs∕GaAs pairs and one dielectric SiO2∕Si3N4 pair as distributed Bragg reflectors (DBRs), respectively. As compared to the nonresonant QD LEDs, the RCLEDs exhibit a forward voltage of 1.13V at 20mA, a peak wavelength of 1.318μm, a narrower full width at half maximum in the electroluminescent spectrum of 14meV at 20mA, a high Q factor of 73.9, a low redshift rate with injection current of 0.033nm∕mA, and a higher light-output power of 28μW at 100mA.

Narrow spectral band monolithic lead chalcogenide on Si mid-IR photodetectors

Resonant cavity-enhanced detectors (RCEDs) with a narrow linewidth and high peak quantum efficiency have been realized for the first time in the mid-IR range. The detectors are fabricated with epitaxial narrow gap lead chalcogenide layers grown epitaxially on Si-substrates. They consist of an epitaxial bottom distributed Bragg mirror, a spacer layer, and the thin absorber layer followed by a metal top layer which forms the photovoltaic detector and in addition acts as top mirror. Devices with peak wavelengths varying from 4 to 8 μm, spectral widths below 1% and quantum efficiencies above 30% have been realised.

Long-wavelength MEMS tunable vertical-cavity surface-emitting lasers with high sidemode suppression

We present a micromechanically tunable long-wavelength vertical-cavity surface-emitting laser with a buried tunnel junction aperture and a stable half-symmetric cavity for full mode control. The conjunction of the active part 'half-VCSEL' and the curved MEMS-mirror in a two-chip assembly enables high output power singlemode emission exceeding 1?mW. Electrothermal actuation of the micromechanical chip allows us to extend the single wavelength performance to a continuously tunable, selectively wavelength-addressable spectrum of 28?nm. The concave curvature and the resulting long air-gap cavity are designed to favour the resonance of the fundamental mode, i.e. to match the phase front predicted by Gaussian beam theory corresponding to the aperture diameter of 10??m. The spatial beam profile of the MEMS-VCSEL is measured in the far-field and compared with a conventional VCSEL with a fixed plane top mirror. The polarization is controlled by a dominating mirror asymmetry. High sidemode suppression over the whole tuning range with respect to both the transverse modes (>40?dB) and the polarization modes (>30?dB) is demonstrated.

SIMS analysis of a multiple quantum well structure in a vertical cavity surface emitting laser using the mixing-roughness-information depth model

We have analyzed a multiple quantum well (MQW) structure in a vertical cavity surface emitting laser (VCSEL) epitaxial wafer using secondary ion mass spectrometry (SIMS). The two energy sputtering method is a very powerful method for providing a depth profile of a GaAs/Al 0.2Ga 0.8As MQW with a sufficient depth resolution and a large number of data points in a practical measurement time. This method consists of rapid high-energy sputtering for a top mirror layer and subsequent low-energy sputtering for an active layer. The resulting profiles were quantitatively evaluated using the mixing-roughness-information depth (MRI) model. The values of C concentration in modulation-doped Al 0.2Ga 0.8As barrier layers have been extracted from the original in-depth concentration profile reconstructed by the MRI model. The relationship between depth resolution of the resulting profile and surface morphology measured by atomic force microscopy (AFM) is also discussed.

High Q-factor colloidal nanocrystal-based vertical microcavity by hot embossing technology

We report on the fabrication and optical characterization of vertical hybrid microcavities in which a layer of colloidal nanocrystals dispersed in an organic matrix is embedded between two inorganic mirrors. The devices are fabricated by a technique based on the unconventional use of the hot embossing technology, which allows a very fine control of the cavity length. The technique exploits a λ-thick microstructured dielectric top mirror pressed onto the bottom one, previously coated with the active layer, to sandwich the cavity and precisely control its thickness. Room-temperature photoluminescence measurements show a Q factor as high as 146 for our devices.

High reflectivity air-bridge subwavelength grating reflector and Fabry-Perot cavity in AlGaAs/GaAs

We present a novel air-bridge subwavelength grating reflector with very high reflectivity to be used as a top mirror in a VCSEL structure. We explain the design method, model the structure using both RCWA and FDTD, and predict the characteristics of a Fabry-Perot structure built with this reflector. We describe the fabrication of the suspended grating.

GaN-Based Green Resonant Cavity Light-Emitting Diodes

GaN-based resonant cavity light-emitting diodes (RCLEDs) have been successfully fabricated on Si substrate by laser lift-off and wafer bonding techniques. A five-pair TiO2/SiO2 dielectric distributed Bragg reflector (DBR) (with 85% reflectivity) and an Ag layer (with 99% reflectivity) were employed as top and bottom mirrors, respectively, for front emission RCLEDs. The room temperature light output power of the RCLED was 1.5 times that of similar LED structures without a top DBR mirror under 20 mA injection current. The cavity modes exhibit a linewidth of 5.5 nm at 525 nm wavelength, which corresponds to a quality factor about 100. Moreover, the full width at half maximum of the emission can be reduced to 35 nm, as a result of the effect of the resonant cavity.

MEMS-tunable 1.55-/spl mu/m VCSEL with extended tuning range incorporating a buried tunnel junction

We present an electrically pumped and micromechanically tunable InP-based vertical-cavity surface-emitting laser operating in the 1.55-/spl mu/m wavelength range. The current confinement is achieved by a buried tunnel junction. The GaAs-based movable top mirror membrane is fabricated separately, assembled on top of the device, and can be actuated electrothermally. A single mode output power of about 1.7 mW and a tuning range of 28 nm was obtained. By the use of an antireflection coating at the semiconductor-air-interface, we were able to extend the tuning range up to 60 nm as expected from one-dimensional simulations.

Effect of resonant cavity in wafer-bonded Green InGaN LED with dielectric and silver mirrors

The green InGaN-based resonant cavity light-emitting diodes (RCLEDs) on Si substrates were fabricated using laser liftoff and wafer bonding techniques. Five-pair TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> --SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> distributed Bragg reflectors (reflectivity: 85%) and an Ag metal layer (reflectivity: 99%) were employed as the top and bottom mirrors, respectively. The light output power of the RCLED at room temperature is 1.5 times the magnitude of a similar structure without a resonant cavity at an injecting current density of 600A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The mode spectrum exhibits a line width of approximately 5.5 nm at the dominant peak wavelength of 525 nm, which indicates a quality factor of 100. Under various injection current densities, a low thermally induced red shift in the 525-nm emission peak was observed. This indicates that the resonant microcavity effect contributes to the stability of electroluminescence emission wavelength

Investigation of Polarization Properties of VCSELs Subject to Optical Feedback From an Extremely Short External Cavity—Part I: Theoretical Analysis

A two modes rate equation model for vertical-cavity surface-emitting lasers (VCSELs) subject to optical feedback from an extremely short external cavity (ESEC) is presented. By making use of it we develop a map of bistability to investigate the parametric dependence of polarization properties of VCSELs in such configuration, finding out a periodic dependence of the polarization switching (PS) currents on the ESEC length. By increasing the external mirror reflectivity we can make this periodic dependence stronger and strongly asymmetric providing the possibility to prevent PS for any injection current achieving polarization stabilization in VCSELs. Further numerical simulations with isotropic and non isotropic feedback show how parameters as the compression coefficients, the frequency splitting between the linearly polarized (LP) modes, the differential gain and the top mirror reflection coefficient, affect the map of bistability.

C-band emission from GaInNAsSbVCSEL on GaAS

The 1.55 /spl mu/m pulsed operation of an optically-pumped GaInNAsSb vertical-cavity surface-emitting laser (VCSEL) is reported. The structure employs a dielectric (SiO/sub 2//TiO/sub 2/) top mirror, while the bottom mirror and active region were grown on GaAs by MBE. Temperature-dependent (10-40/spl deg/C) laser measurements were made for an as-grown sample and an annealed sample, both having a room-temperature lasing wavelength of 1547 nm. Results indicate an annealing-induced blue-shift of the gain peak.

C-band emission from GaInNAsSb VCSEL on GaAs

The 1.55 µm pulsed operation of an optically-pumped GaInNAsSb vertical-cavity surface-emitting laser (VCSEL) is reported. The structure employs a dielectric (SiO2/TiO2) top mirror, while the bottom mirror and active region were grown on GaAs by MBE. Temperature-dependent (10–40°C) laser measurements were made for an as-grown sample and an annealed sample, both having a room-temperature lasing wavelength of 1547 nm. Results indicate an annealing-induced blue-shift of the gain peak.

Highly selective and compact tunable MOEMS photonic crystal Fabry-Perot filter

The authors report a compact and highly selective tunable filter using a Fabry-Perot resonator combining a bottom micromachined 3-pair-InP/air-gap Bragg reflector with a top photonic crystal slab mirror. It is based on the coupling between radiated vertical cavity modes and waveguided modes of the photonic crystal. The full-width at half maximum (FWHM) of the resonance, as measured by microreflectivity experiments, is close to 1.5nm (around 1.55 microm). The presence of the photonic crystal slab mirror results in a very compact resonator, with a limited number of layers. The demonstrator was tuned over a 20nm range for a 4V tuning voltage, the FWHM being kept below 2.5nm. Bending of membranes is a critical issue, and better results (FWHM=0.5nm) should be obtained on the same structure if this technological point is fixed.

Tunable Fabry-Perot surface micromachined interferometer-experiments and modeling

We present an optical tunable Fabry-Perot micromachined interferometer. The device is monolithically integrated with a p+-n photodiode on a silicon substrate, providing an adequate positioning of the photonic and microoptical components. The Fabry-Perot micro-interferometer consists of two parallel mirrors and lets the light with a particular wavelength pass through. The wavelength depends on the gap between the mirrors. We can change the gap of the micro-mechanical Fabry-Perot interferometer by applying a voltage to the mirrors, an electrostatic force inducing an attraction between the substrate and the top mirror. A simulation of the mechanical behavior was performed based on finite elements, using CoventorWare software. The method included an electro-mechanical simulation for a square parallel plate actuation with four connecting beams. The finite elements method (FEM) simulations of the device (the Fabry-Perot tunable filter) are performed for optimizing the design parameters in order to model the overall system performance, both the steady-state behavior and dynamic response.

Engineering of optical active microcavities based on color centers in LiF by ion implantation

Abstract For the first time active planar optical microcavities with a thin colored lithium fluoride film as spacer have been fabricated by ion implantation. Irradiation has been realized through the top Bragg mirror of the passive microcavity, already fully deposited, to produce stable visible-emitting F2 and F 3 + color centers in the LiF film. The spectral and spatial emission features of the microcavities demonstrate the feasibility of such an irradiation method and the possibility of controlling the radiative properties of compact light sources based on point defects in this interesting material.

1.55 μ m GaInNAs resonant-cavity-enhanced photodetector grown on GaAs

We report the design, growth, fabrication, and characterization of a GaAs-based resonant-cavity-enhanced (RCE) GaInNAs photodetector operating at 1.55μm. The structure of the device was designed using a transfer-matrix method (TMM). By optimizing the molecular-beam epitaxy growth conditions, six GaInNAs quantum wells were used as the absorption layers. Twenty-five (25)- and 9-pair GaAs∕AlAs-distributed Bragg reflectors were grown as the bottom and top mirrors. At 1.55μm, a quantum efficiency of 33% with a full width at half maximum of 10nm was obtained. The dark current density was 3×10−7A∕cm2 at a bias of 0V and 4.3×10−5A∕cm2 at a reverse bias of 5V. The primary time response measurement shows that the device has a rise time of less than 800ps.