AlGaAs Distributed Bragg Reflectors Research Articles

Study of monolithically integrated 940 nm AlGaAs distributed Bragg reflectors on graded GaAsP/bulk Si substrates

We report the fabrication of monolithically integrated 940 nm AlGaAs distributed Bragg reflectors (DBRs) on graded GaAsP/Si substrates. Low-density surface bumps and cross-hatch patterns were observed on the DBR surfaces. Cross-sectional DBR layers are smooth and flat. The reflectance spectra of the GaAsP/Si DBRs have lower intensities than those of the GaAs DBRs and have double peaks. Transfer matrix method calculations, surface scratch and polishing tests were conducted, which suggest that the surface cross-hatch was the cause of the inferior DBR reflectance spectra.

Simulation and Analysis of the Optical Characteristics of Cylindrical Micropillars with InAs/GaAs Quantum Dots

The optical characteristics of vertical cylindrical micropillars with AlGaAs distributed Bragg reflectors and InAs/GaAs quantum dots, which are designed for the fabrication of single-photon sources, have been studied. The effect of parameters such as the inclination angle of sidewalls, partial oxidation of AlGaAs layers, and deviation of quantum dots from the central axis of a micropillar on the Purcell factor and the radiation extraction efficiency has been numerically simulated by the finite-difference time-domain method. The allowable ranges of the listed parameters have been determined for cylindrical vertical 920-nm micropillars. The comparison of the calculations performed with the refined refractive indices of the used materials at cryogenic temperatures with the measured characteristics of the fabricated micropillar structures has confirmed the adequacy of the used models.

Monolithic integration of AlGaAs distributed Bragg reflectors on virtual Ge substrates via aspect ratio trapping

High quality AlxGa1-xAs distributed Bragg reflectors (DBRs) were successfully monolithically grown on on-axis Si (100) substrates via a Ge layer formed by aspect ratio trapping (ART) technique. The GaAs/ART-Ge/Si-based DBRs have reflectivity spectra comparable to those grown on conventional bulk off-cut GaAs substrates and have smooth morphology and reasonable periodicity and uniformity. Antiphase domain formation is significantly reduced in GaAs on ART-Ge/Si substrates, and etch pit density of the GaAs base layer on the ART-Ge substrates ranges from 105 to 6 × 106 cm−2. These results paved the way for future VCSEL growth and fabrication on these ART-Ge substrates and also confirm that virtual Ge substrates via ART technique are effective Si platforms for optoelectronic integrated circuits.

Growth and characterization of electrically pumped red-emitting VCSEL with embedded InP/AlGaInP quantumdots

In this letter, we report on laser light emission, in the red spectral range, of electrically pumped self-assembled InP quantum dots which were embedded in a microcavity structure realized by monolithically grown highly reflective AlGaAs distributed Bragg reflectors. Common semiconductor laser processing steps were used to fabricate stand-alone index-guided vertical-cavity surface-emitting lasers with oxide apertures for optical transverse mode confinement and electrical current constriction. Ultra-low threshold current densities of around 10 A/cm 2 and room temperature lasing were achieved.

Low threshold and room-temperature lasing of electrically pumped red-emitting InP/(Al0.20Ga0.80)0.51In0.49P quantum dots

In this letter, we report on laser light emission in the red spectral range. Self-assembled InP quantum dots being electrically pumped were embedded in a microcavity mesa realized by monolithically grown high-reflectivity AlGaAs distributed Bragg reflectors. Common semiconductor laser processing steps were used to fabricate stand-alone index-guided vertical-cavity surface-emitting lasers with oxide apertures for optical transverse mode confinement and electrical current constriction. Ultra-low threshold current densities of around 10A/cm2 and room temperature lasing were achieved.

Room-temperature lasing of electrically pumped red-emitting InP/(Al0.20Ga0.80)0.51In0.49P quantum dots embedded in a vertical microcavity

We demonstrate electrically pumped laser light emission in the visible (red) spectral range using self-assembled InP quantum dots embedded in a microcavity mesa realized by monolithically grown high-reflectivity AlGaAs distributed Bragg reflectors. We used common semiconductor laser processing steps to fabricate stand-alone index-guided vertical-cavity surface-emitting lasers with oxide apertures for optical wave-guiding and electrical current constriction. Ultra-low threshold of around 10 A/cm2 and room temperature lasing were demonstrated. Additionally, the temperature independence of the threshold current, which was predicted in theory for quantum dot lasers, is displayed.

Increased single-photon emission from InP/AlGaInP quantum dots grown on AlGaAs distributed Bragg reflectors

InP/GaInP quantum dots emitting in the red spectral range have been grown on an AlGaAs distributed Bragg reflector in order to increase the single-photon emission efficiency. We have observed an increase in ensemble photoluminescence by a factor of 28 in comparison to the reference InP/GaInP quantum dots grown without such a reflector underneath. Photon correlation measurements performed under pulsed excitation show a clear antibunching behavior ( g ( 2 ) ( 0 ) = 0.17 ) as expected for a single-photon emitter. Using aluminum containing barriers to surround the quantum dots the ensemble luminescence intensity could be increased by a factor of 500 at 240 K in comparison to the reference sample at 240 K.

Red single-photon emission from an InP∕GaInP quantum dot embedded in a planar monolithic microcavity

Using micro-photoluminescence, we demonstrate single-photon emission in the visible (red) spectral range using self-assembled InP quantum dots embedded in a planar microcavity realized by monolithically grown high reflectivity AlGaAs distributed Bragg reflectors. A full width at half maximum of 130μeV at 5K was observed from a single quantum dot coupled to the fundamental cavity resonance. Photon correlation measurements performed under continuous wave excitation show a clear antibunching behavior [g(2)(0)=0.13] as expected for a single-photon emitter. Saturation count rates up to 1.5MHz (8.1MHz into the first lens, with an extraction efficiency of 4.1%) were observed.

Focused ion beam etching for the fabrication of micropillar microcavities made of III-V semiconductor materials

The authors demonstrate a simple approach for the construction of single photon sources utilizing focused ion beam (FIB) etching, a maskless fabrication technique. Here they use FIB with gas-assisted etching to fabricate micropillar microcavities from a GaAs∕AlGaAs distributed Bragg reflector planar cavity containing self-assembled InAs quantum dots. Using a 1.5μm square pillar, they demonstrate a single photon source where the two photon emission is suppressed by a factor of 3.8. They believe this to be the first example of a FIB fabricated pillar single photon source.

GaSb quantum-well-based “buffer-free” vertical light emitting diode monolithically embedded within a GaAs cavity incorporating interfacial misfit arrays

The authors demonstrate a monolithic, electrically injected, vertically emitting GaSb∕AlGaSb light emitting diode (LED) emitting at 1.6μm comprised of a hybrid GaAs∕GaSb-based structure. The LED is comprised of a GaSb∕AlGaSb quantum well/barrier active region embedded within high index contrast GaAs∕AlGaAs distributed Bragg reflectors (DBRs) using two interfacial misfit (IMF) arrays to relieve the strain induced from the high 8% lattice mismatch between the material systems. The first IMF is formed under compressive strain conditions to enable strain-free, defect-free deposition of GaSb active region directly on the lower GaAs∕AlAs DBRs without need for thick buffer. The second IMF is formed under tensile conditions to enable the upper GaAs∕AlAs DBRs on the GaSb active region. The device demonstrates a maximum output power of 3.5μW. Initial diode optical and electrical characteristics along with IMF band structure are discussed.

1.3-/spl mu/m InAs-InGaAs quantum-dot vertical-cavity surface-emitting laser with fully doped DBRs grown by MBE

We report InAs-InGaAs quantum-dot vertical-cavity surface-emitting lasers (VCSELs) grown by molecular beam epitaxy with fully doped n- and p-doped AlGaAs distributed Bragg reflectors and including an AlAs layer to form a current and waveguiding aperture. The metal contacts are deposited on a topmost p/sup +/-GaAs contact layer and on the bottom surface of the n/sup +/-GaAs substrate. This conventional selectively oxidized top-emitting device configuration avoids the added complexity of fabricating intracavity or coplanar ohmic contacts. The VCSELs operate continuous-wave at room temperature with peak output powers of 0.33 mW and differential slope efficiencies up to 0.23 W/A. The peak lasing wavelengths are near 1.275 μm, with a sidemode suppression ratio of 28 dB.

High Speed Heterostructure Metal-Semiconductor-Metal Photodetectors

A. Colaa,∗, B. Nabet, Xiying Chen and F. Quaranta CNR-IMM sez. di Lecce, via Arnesano 73100 Lecce, Italy Electrical and Computer Engineering Dept., Drexel University 318 Commonwealth, Philadelphia, PA, 19104, USA In this work we review the properties of a class of metal−semiconductor– metal photodetectors based on heterojunction structures. Particularly, an AlGaAs/GaAs device is detailed in which the absorption region is in the GaAs layer, and a two-dimensional electron gas is formed at the heterointerface due to δ-doping of the widegap material. This heterostructure metal– semiconductor–metal photodetector also contains an AlGaAs distributed Bragg reflector that forms a resonant cavity for detection at 850 nm. The beneficial effect of the two-dimensional electron gas in the GaAs absorption layer in terms of speed and sensitivity is demonstrated by comparing samples with and without doping in the AlGaAs layer. The design and the physical properties of the grown epitaxial structure are presented, together with the static and dynamic characteristics of the device in time domain. In particular, photocurrent spectra exhibit a 30 nm wide peak at 850 nm, and time response measurements give a bandwidth over 30 GHz. A combination of very low dark current and capacitance, fast response, wavelength selectivity, and compatibility with high electron mobility transistors makes this device suitable for a number of application areas, such as Gigabit and 10 Gigabit Ethernet, wavelength division multiplexing, remote sensing, and medical applications.

Implant isolation of AlGaAs multilayer DBR

AlGaAs distributed Bragg reflector (DBR) structures isolation by proton irradiation was studied. The evolution of n- and p-type DBR structures lateral sheet resistance with the irradiated proton dose was measured. The vertical isolation behavior was also obtained and compared to the lateral one. No significant differences were observed. The implantation maximum energy for these structures was estimated. Thermal stability of DBR vertical isolation was studied. A 500 °C stability was obtained for samples implanted to a dose 2.5 times greater than the threshold dose of isolation.

On the Reflectivity Spectrum of Implanted AlGaAs Distributed Bragg Reflector

In this study, we investigated the influence of ion implantation and post-implantation rapid thermal anneal (RTA) on the reflectivity spectrum of an AlGaAs distributed Bragg reflector (DBR). The peak wavelength of the reflectivity spectrum shifts toward longer wavelengths and the background reflectance increases after ion implantation. The calculated spectrum agrees well with the experimental observation. It can be used to understand the mechanisms of ion implantation on the reflectivity spectra. Four different ions (H+, O+, Si+ and P+) were implanted into DBR for comparison. Among these samples, the Si-implanted DBR has the largest amount of red-shift, and the hydrogen-implanted DBR are almost the same as unimplanted. In addition, post-implantation RTA would shift the reflectivity band back to its original position and lead to the recovery of the background reflectance, but degrade peak reflectance.

Carrier-confined vertical-cavity semiconductor optical amplifiers for higher gain and efficiency

Vertical-cavity semiconductor optical amplifiers (VCSOAs) are interesting devices because of their small form factor, potential low manufacturing cost, high coupling efficiency to optical fiber, and polarization-independent gain. We present an overview of the properties of VCSOAs, as well as emerging applications for this new class of devices. We present general design rules and analyze how the mirror reflectivity affects the properties of the VCSOA. Experimental results of carrier-confined, optically pumped VCSOAs operating at 1.3-μm wavelength are presented. The devices were fabricated by wafer bonding high-quality AlGaAs distributed Bragg reflectors (DBRs) to an InGaAsP/InP active region. A carrier-confining structure was formed on the active region before the top mirror was bonded to the sample. These VCSOAs show the highest fiber-to-fiber gain (17 dB) and the lowest noise figure (6.1 dB) of any long-wavelength VCSOAs to date. VCSOAs should find applications as low-cost, single-channel amplifiers, amplifying filters, amplifying switches or modulators, as well as in two-dimensional array applications such as optical interconnects. We demonstrate the use of VCSOAs for optical preamplification at 10 Gb/s. Using an 11-dB gain VCSOA, the sensitivity of a regular p-i-n detector was increased by 7 dB resulting in a receiver sensitivity of -26.2 dBm.

Resonant cavity light-emitting diodes at 660 and 880 nm

Resonant cavity light-emitting diodes (RCLEDs) operating at λ≅660 nm and λ≅880 nm have been fabricated and studied. The RCLED layer structures consisted of 1− λ thick cavities sandwiched between AlGaAs distributed Bragg reflectors. The cavities were detuned to improve temperature stability and light extraction. The temperature induced red-shifts in the peak emission wavelength were found to be 0.14 and 0.22 nm °C −1 for the 660- and 880-nm devices, respectively.

Widely tunable 1.5 [micro sign]m micromechanical optical filter using AlOx/AlGaAs DBR

The authors demonstrate, for the first time, a wavelength tunable optical filter at 1.55 /spl mu/m using micromechanical tuning of a Fabry-Perot resonator with an AlO/sub x//AlGaAs distributed Bragg reflectors (DBR). The use of thermally oxidised AlAs layers, resulting an ultrawide bandwidth, dramatically increased the tuning range and efficiency of the resonator. Very efficient continuous tuning of >50 nm with only a 0.95 V tuning voltage was achieved. The tuning range, limited by our test laser, is expected to be expandable to hundreds of nm.

Tunable high-power AlGaAs distributed Bragg reflector laser diodes

Power exceeding 200 mW from high-power tunable distributed Bragg reflector (TDBR) lasers have been achieved. The low power consumption tuning mechanism is described, with a wavelength tuning of > 10 nm. A 20 000 h lifetest on DBR lasers is presented.

Cavity-Induced Changes of Spontaneous Emission Lifetime in One-Dimensional Semiconductor Microcavities.

Spontaneous emission lifetime in a one-dimensional AlGaAs distributed Bragg reflector microcavity has been systematically measured as a function of emission wavelength tuned by the quantum-confined Stark effect in order to confirm the cavity-induced alteration of the SE lifetime. The result manifests a substantial cavity-induced fractional change of the exciton decay times, $\ensuremath{\sim}$30% around the on-axis resonant wavelength, despite the relatively large broadening of the excitonic emission being comparable to the cavity resonance width in the low- $Q$ cavity.

Partial top dielectric stack distributed Bragg reflectors for red vertical cavity surface emitting laser arrays

Room temperature continuous wave operation of red (/spl lambda/ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /spl sim/660 nm) vertical cavity surface emitting laser arrays is reported. The 1×64 arrays have a pitch of 100 μm with device diameters of 15 μm. Grown by metalorganic vapor phase epitaxy, the devices consist of an AlGaInP strained quantum well optical cavity active region surrounded by AlGaAs distributed Bragg reflectors (DBR's). The top coupling DBR includes a partial dielectric stack, deposited after implanted device fabrication. All 64 devices operate simultaneously with peak output powers >0.45 mW, threshold currents <1.5 mA, and threshold voltages /spl les/2.7 V. The differential quantum efficiencies exceed 10%.