Showing papers by "Guo-En Chang published in 2017"

Sn-based waveguide p-i-n photodetector with strained GeSn/Ge multiple-quantum-well active layer.

Abstract: We report on Sn-based p-i-n waveguide photodetectors (WGPD) with a pseudomorphic GeSn/Ge multiple-quantum-well (MQW) active layer on a Ge-buffered Si substrate. A reduced dark-current density of 59 mA/cm2 was obtained at a reverse bias of 1 V due to the suppressed strain relaxation in the GeSn/Ge active layer. Responsivity experiments revealed an extended photodetection range covering the O, E, S, C, and L telecommunication bands completely due to the bandgap reduction resulting from Sn-alloying. Band structure analysis of the pseudomorphic GeSn/Ge quantum well structures indicated that, despite the stronger quantum confinement, the absorption edge can be shifted to longer wavelengths by increasing the Sn content, thereby enabling efficient photodetection in the infrared region. These results demonstrate the feasibility of using GeSn/Ge MQW planar photodetectors as building blocks of electronic-photonic integrated circuits for telecommunication and optical interconnection applications.

Intensity-detection-based guided-mode-resonance optofluidic biosensing system for rapid, low-cost, label-free detection

Abstract: We present an intensity-detection-based optofluidic biosensing system with a disposable guided-mode-resonance (GMR) biosensor chip for low-cost, rapid, label-free biosensing. The developed sensing system consists of a low-cost spectrally limited light-emitting diode (LED) as the light source and a photodetector as the optical receiver. This detection instrument can transform the GMR wavelength shift induced by the change in the local refractive index (RI) near the chip’s grating surface into change in the light intensity, thus enabling label-free, real-time detection. RI measurement experiments in both the transmission and reflection modes are performed to study the corresponding sensing mechanisms and compare detection performance. The results indicate that this sensing system operating in the reflection mode can achieve a superior RI resolution of 4 . 10 × 10 - 5 RIU over a wide linear detection range of 0.04 RIU. Label-free biomolecular interaction experiments show that a low limit of detection (LOD) of 7.5 × 10−8 g/ml for dinitro-phenyl (DNP)/anti-DNP interactions can be achieved, thus confirming the our system’s sensitivity. The present investigation demonstrates a low-cost, compact, high-performance optofluidic biosensing system for rapid and sensitive biochemical detection that can be utilized for a wide variety of applications.

Micromachining Microchannels on Cyclic Olefin Copolymer (COC) Substrates with the Taguchi Method.

Abstract: Micromilling is a straightforward approach to the manufacture of polymer microfluidic devices for applications in chemistry and biology. This fabrication process reduces costs, provides a relatively simple user interface, and enables the fabrication of complex structures, which makes it ideal for the development of prototypes. In this study, we investigated the influence of micromilling parameters on the surface roughness of a cyclic olefin copolymer (COC) substrate. We then employed factor analysis to determine the optimal cutting conditions. The parameters used in all experiments were the spindle speed, the feed rate, and the depth of cut. Roughness was measured using a stylus profilometer. The lowest roughness was 0.173 μm at a spindle speed of 20,000 rpm, feed rate of 300 mm/min, and cut depth of 20 μm. Factor analysis revealed that the feed rate has the greatest impact on surface quality, whereas the depth of cut has the least impact.

GeSn/Ge quantum well photodetectors for short-wave infrared photodetection: experiments and modeling

Abstract: Group-IV GeSn material systems have recently considered as a new material for sensitive photodetection in the short-wave infrared (SWIR) region The introduction of Sn into Ge can effectively narrow the bandgap energies, thereby extending the absorption edges toward the longer wavelengths and enabling effective photodetection in SWIR region Here we present an experimental and modeling study of GeSn/Ge quantum well (QW) photodetectors on silicon substrates for effective SRIW photodetection Epitaxial growth of pseudomorphic GeSn/Ge QW structures was realized on Ge-buffered silicon substrates using low-temperature molecular beam epitaxy Normal incident GeSn/Ge QW photodetectors were then fabricated and characterized The optical responsivity experiments demonstrate that the photodetection cutoff wavelengths is extended to beyond 1800 nm, enabling effective photodetection in SWIR spectral region We then develop theoretical models to calculate the composition-dependent strained electron band structures, oscillation strengths, and optical absorption spectra for the pseudomorphic GeSn/Ge QW structures The results show that Ge1-xSnx well sandwiched by Ge barriers can achieve a critical type-I alignment at Γ point to provide necessary quantum confinement of carriers With an increase in the Sn content, the band offsets between the GeSn well and Ge barreirs increases, thus enhancing the oscillation strengths of direct interband transitions In addition, despite stronger quantum confinement with increasing Sn content, the absorption edge can be effectively shifted to longer wavelengths due to the direct bandgap reduction caused by Sn-alloying These results suggest that GeSn/Ge QW photodetectors are promising for low-cost, high-performance SWIR photodetection applications