Ko-Hsin Lee

Integration of AlInGaAs-MQW Fabry–Pérot Lasers With Emission at Two Wavelength Ranges via Quantum-Well Intermixing

We demonstrate ridge waveguide lasers based on AlInGaAs multiple quantum wells emitting at 1434 and 1541 nm on the same laser bar using quantum-well intermixing with dielectric capping layers. The internal quantum efficiencies are measured to be 61% and 72% and the internal losses are 49 and 23 cm-1 for lasers with intermixing promoted and inhibited, respectively. The characteristic temperatures are found to be approximately 50 K for lasers emitting around 1433 nm and 75 K for those emitting around 1541 nm.

Characterization of germanium/silicon p-n junction fabricated by low temperature direct wafer bonding and layer exfoliation

The current transport across a p-Ge/n-Si diode structure obtained by direct wafer bonding and layer exfoliation is analysed. A low temperature anneal at 400 °C for 30 min was used to improve the forward characteristics of the diode with the on/off ratio at −1 V being >8000. Post anneal, the transport mechanism has a strong tunnelling component. This fabrication technique using a low thermal budget (T ≤ 400 °C) is an attractive option for heterogeneous integration.

Zero-Bias High-Speed Edge-Coupled Unitraveling-Carrier InGaAs Photodiode

The traveling-wave edge-coupled unitraveling-carrier (UTC) photodiode was designed and fabricated for zero-bias high-speed communication system application. A 40-μm-long 5-μm-wide UTC waveguide device demonstrated 13-GHz 3-dB bandwidth and up to 10-mA photocurrent without saturation in our measurement range under zero bias.

Compact Electroabsorption Modulators for Photonic Integrated Circuits, Using an Isolated Pedestal Contact Scheme

We demonstrate a shallow ridge waveguide, lumped element electroabsorption modulator (EAM) based on AlInGaAs multiple quantum wells, operating with input powers up to 8 dBm. The device was isolated between two DC controlled sections, using angled etched slots in the waveguide, minimizing optical feedback, while also providing 40-KΩ resistance between devices. The EAM uses a planar isolated pedestal contact with a benzocyclobutene bridge, allowing for a small contact footprint of just 0.024 mm2, while being suitable for flip-chip packaging. The parasitic capacitance was measured to be 19.6 fF, and the EAM has a f3dB bandwidth of 42 GHz.

Quantum well intermixing in AlInGaAs MQW structures through impurity-free vacancy method

We report on quantum well intermixing of AlInGaAs-MQWs using the impurity-free vacancy diffusion method with dielectric capping layers which has potential for realization of photonic integrated circuits. The extent of the bandgap shifts with respect to different dielectric capping layers and alloy temperatures are investigated. The intermixing inhibitor and promoter are then integrated using combination of SiO2 and SiNx dielectric capping layers which shows a differential photoluminescence wavelength more than 110 nm. Based on this developed intermixing technique, we have fabricated AlInGaAs-InP based material stripe lasers emitting at two different wavelength ranges centered at 1519 nm and 1393 nm respectively. Characterizations including the current-voltage and electroluminescence measurements show that the integration of two-bandgaps can be achieved and furthermore a differential wavelength in lasing spectra up to 120 nm is demonstrated.

SiNx-induced intermixing in AlInGaAs/InP quantum well through interdiffusion of group III atoms

We analyze the composition profiles within intermixed and non-intermixed AlInGaAs-based multiple quantum wells structures by secondary ion mass spectrometry and observe that the band gap blue shift is mainly attributed to the interdiffusion of In and Ga atoms between the quantum wells and the barriers. Based on these results, several AlInGaAs-based single quantum well (SQW) structures with various compressive strain (CS) levels were grown and their photoluminescence spectra were investigated after the intermixing process involving the encapsulation of thin SiNx dielectric films on the surface followed by rapid thermal annealing. In addition to the annealing temperature, we report that the band gap shift can be also enhanced by increasing the CS level in the SQW. For instance, at an annealing temperature of 850 °C, the photoluminescence blue shift is found to reach more than 110 nm for the sample with 1.2%-CS SQW, but only 35 nm with 0.4%-CS SQW. We expect that this relatively larger atomic compositional g...

Quantum well intermixing in AlInGaAs QW structures through the interdiffusion of group III atoms

In this paper, the composition profiles within intermixed AlInGaAs-based multiple quantum wells structure are analyzed by secondary ion mass spectrometry and the bandgap blue shift is found to be mainly attributed to the interdiffusion of In and Ga between the quantum wells and barriers. Based on these results, AlInGaAs-based single quantum well structures with various compressive strain (CS) levels are then investigated and we report an enhancement of the bandgap shift by increasing the compressive strain level in the SQW. For instance, at an annealing temperature of 850°C, the photoluminescence blue shift can reach more than 110 nm for the sample with 1.2%-CS SQW, but only 35 nm with 0.4%-CS SQW. The indium composition ratios are designed to be 0.59 and 0.71 for the 0.4% and 1.2%-CS quantum wells, respectively, as opposed to 0.53 for the lattice-matched barrier. This relatively larger atomic compositional gradient between the CS quantum well and barrier is expected to facilitate the atomic interdiffusion and lead to the more pronounced bandgap shift.

Integration of low-pass filter with optical receiver using quantum well intermixing

We report on monolithic integration of a low-pass optical filter with an optical receiver composed of a semiconductor optical amplifier (SOA) and p-i-n photodiode (PD) using quantum well intermixing on an AlInGaAs-based multiple quantum well structure. The bandgap energy of the low-pass optical filter has been increased deliberately relative to the SOA and PD sections. The amplified spontaneous emission for photon energy higher than the filter bandgap is then absorbed prior to entering to PD and the optical noise can thus be reduced. By adjusting the reverse bias applied to optical filter and PD, a coarse tuning on the detection wavelength range can be obtained.

Enhanced lensed fiber for Si-nanowire coupling

We propose a lensed fiber design exhibiting good coupling efficiency together with a long working distance for the coupling of silicon based nanophotonic waveguides to a single mode optical fiber. The lensed fiber consists of a coreless fiber tip coated with a high refractive index material. Numerical simulations show that the coupling loss as low as −0.5 dB can be achieved with a working distance of ∼37 µm for coupling from a nanowire waveguide with a mode field diameter of 700 nm to our lensed fiber. This optimized fiber design has a radius of curvature of 60 µm, a 800 µm-long coreless fiber section, and a 10 µm-thick coating layer with an index of 3.7.

Design and fabrication of uni-traveling-carrier InGaAs photodiodes

Photodiode (PD) is a key component in optical transmission and optical measurement systems. In this paper, we present the design and fabrication of traveling-wave edge-coupled Unitraveling Carrier (UTC) PD. The fabricated UTC PD with 40μm×5μm waveguide shows 3dB bandwidth 13GHZ and 32GHz under 0 biases and -1V respectively. In parallel, PIN PD was also fabricated for comparison and only shows 4GHz and 18GHz under same bias conditions. This indicates the UTC PD is superior to the PIN PD for higher speed operation, especially in application of system without power supply.