Chad S. Wang

Monolithically integrated active components: a quantum-well intermixing approach

As the demand for bandwidth increases, the communications industry is faced with a paradigm shift. Photonic integration is a key technology that will facilitate this shift. Monolithic integration allows for the realization of highly functional optical components, called photonic integrated circuits. Herein, we discuss the advantages and potential applications of photonic integration, and after a brief overview of various integration techniques, provide a detailed look at our work using a novel quantum well intermixing processing platform.

Detrimental effect of impact ionization in the absorption region on the frequency response and excess noise performance of InGaAs-InAlAs SACM avalanche photodiodes

It is shown that optimization of the electric field profile in the absorption region of separate absorption, charge, and multiplication InGaAs-InAlAs avalanche photodiodes is critical to achieve low excess noise and high gain bandwidth product.

DC Characteristics of AlGaAs/GaAs/GaN HBTs Formed by Direct Wafer Fusion

We have fabricated AlGaAs/GaAs/GaN heterojunction bipolar transistors (HBTs) formed by direct wafer fusion with different fusion temperatures. By employing a low wafer fusion temperature of 550 degC, current gains as high as ~9 and output currents as high as ~65 mA (emitter size of 100times120 mum2) were obtained. The effective minority carrier lifetime in the base was estimated to have decreased ~20 times due to the fusion process. In comparison, HBTs produced with higher wafer fusion temperatures (600 degC and 650 degC) exhibit lower current gains (~2-3) and higher base-collector leakage currents

High-speed and low-noise SACM avalanche photodiodes with an impact-ionization-engineered multiplication region

A separate absorption, charge, and multiplication In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode with an impact-ionization-engineered multiplication region is reported. By implementing an electric field gradient in the multiplication region, better control of impact-ionization can be achieved. Gain-bandwidth product of 160 GHz and excess noise factor with an equivalent k value of 0.1 are demonstrated.

Design and demonstration of novel QW intermixing scheme for the integration of UTC-type photodiodes with QW-based components

We present the design and demonstration of unitraveling carrier (UTC) photodiodes fabricated using a novel quantum-well (QW) intermixing and metal-organic chemical vapor deposition (MOCVD) regrowth fabrication platform. The photodiodes discussed here were realized on the same chip as high gain centered QW active regions, intermixed passive centered well waveguides, and low optical confinement offset QW active regions regrown over intermixed wells. This demonstration lifts previous constraints imposed on high functionality photonic circuits, which forced a common waveguide architecture in the detector, laser, and amplifier by validating a platform suited for the monolithic integration of UTC photodiodes into photonic integrated circuits comprised of widely tunable high gain laser diodes, high efficiency modulators, and low optical confinement high saturation power semiconductor optical amplifiers. In this manuscript we focus on the design and performance of UTC photodiodes fabricated on intermixed QWs using this novel scheme. The photodiodes exhibit /spl sim/90% internal quantum efficiency, excellent photocurrent handling capabilities, and minimal response roll-off over the 20 GHz of our testing capability. The 40 Gb/s operation was achieved with the demonstration of open eye diagrams.

Sensitivity and scattering in a monolithic heterodyned laser biochemical sensor

We discuss the sensitivity of a novel biochemical sensor based on the heterodyne detection of the optical frequency shift between two monolithically integrated frequency-tunable lasers. A hundred-fold improvement may be obtained by replacing the traditional ridge waveguide structure with a quasisymmetrically clad channel waveguide, which we demonstrate in a simple coupled-cavity sensor. In most cases, the optical scattering from biomolecules bound to such a waveguide will be negligible.

Photocurrent spectroscopy for quantum-well intermixed photonic integrated circuit design

Photocurrent spectroscopy is used to characterize band edges in quantum-well intermixed InGaAsP material lattice matched to InP. The band edge absorption data is used as a design tool to predict the dc performance of electroabsorption modulators, and is shown to agree well with data obtained from actual devices. In addition, we demonstrate the presence of an exciton peak in InGaAsP quantum wells, and present its evolution as a function of quantum-well intermixing and reverse bias voltage.

High-differential-quantum-efficiency, long-wavelength vertical-cavity lasers using five-stage bipolar-cascade active regions

We present five-stage bipolar-cascade vertical-cavity surface-emitting lasers emitting at 1.54μm grown monolithically on an InP substrate by molecular beam epitaxy. A differential quantum efficiency of 120%, was measured with a threshold current density of 767A∕cm2 and voltage of 4.49V, only 0.5V larger than 5×0.8V, the aggregate photon energy. Diffraction loss study on deeply etched pillars indicates that diffraction loss is a major loss mechanism for such multiple-active region devices larger than 20μm. We also report a model on the relationship of diffraction loss to the number of active stages.

Gain degradation mechanisms in wafer fused AlGaAs∕GaAs∕GaN heterojunction bipolar transistors

The authors have compared AlGaAs∕GaAs∕GaN heterojunction bipolar transistors (HBTs) formed by wafer fusion with AlGaAs∕GaAs∕GaAs as-grown HBTs subject to high temperature annealing conditions similar to those used in the wafer fusion process. The high temperature annealing alone is found to cause gain degradation by a factor of 2–6, a result of reduction in minority carrier lifetime in the base. Detailed analysis indicates that the fused HBTs also suffer from higher recombination in the emitter-base junction, exacerbated base degradation as well as effective potential barriers formed at the GaAs base/GaN collector junction.

High-speed tapered-oxide-apertured 980 nm VCSELs supporting data rates up to 30 Gb/s

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