Yen-Ting Pan

Antireflective silicon surface with vertical-aligned silicon nanowires realized by simple wet chemical etching processes

Silicon antireflection is realized with vertical-aligned SiNWs by using improved metal-induced etching technique. The spectral responses of the transmission, reflection, and absorption characteristics for the SiNWs of different lengths are investigated. In order to realize short SiNWs to provide sufficiently low reflection, a post chemical etching process is developed to make the nanowires have a larger length fluctuation and/or tapered structure. The use of short SiNWs can allow a faster process time and avoid the sub-bandgap absorption that frequently occurs in long nanowires. Short SiNWs can also provide more compatible material structure and fabrication procedures than long ones can for applying to make optoelectronic devices. Taking the applications to solar cells as examples, the SiNWs fabricated by the proposed technique can provide 92% of solar weighted absorption with about 720 nm long wires because of the resultant effective graded index and enhanced multiple optical scattering from the random SiNW lengths and tapered wires after KOH etching.

Realization and Characterization of Aligned Silicon Nanowire Array With Thin Silver Film

Wafer-scale fabrication of aligned and uniform silicon nanowire (SiNW) arrays is achieved with good controllability and reproducibility by depositing a thin silver film on a silicon surface prior to wet etching. Fast SiNW formation with a rate of 1.4 μm/min is achieved with optimized process condition, while lower etching rate enables finer SiNW formation in a small open area. Realized SiNWs are demonstrated to have good material and optical properties. With the help of aligned SiNWs, we demonstrate the fabrication of a black nonreflecting silicon surface with a surface reflectivity of around 2-4% uniformly over a 4-in wafer area. This material is expected to be promising as a building block for various applications due to its low-cost and mass-producible fabrication and excellent characteristics.

Holographic realization of hexagonal two dimensional photonic crystal structures with elliptical geometry

A complete investigation of holographic photonic crystal structures has been conducted. From both theoretical and experimental results, profiles of resultant patterns under different process conditions can be estimated and controlled. The use of antireflection layers is crucial for realizing submicron photonic crystals with good uniformity over a large area. We successfully realize submicron-scale photonic crystal templates on silicon substrates with an aspect ratio of 2.5 and good quality by a laser holography technique. The samples are highly uniform in an area of >2×2 cm2 and present good reproducibility. A lift-off process is performed to transfer inversed pillar patterns into a chromium hard mask for the following dry etching into silicon substrates. A single-step deep reactive ion etching with controlled mixture of Ar/SF6/C4F8 gases is used to directly transfer pillar patterns into silicon. Transferred patterns with a high aspect ratio and vertical sidewalls (no scalloping) are demonstrated over a l...

Trend and Applications of Tunable Semiconductor Lasers

Tunable semiconductor lasers have been under intense research interests for the past decades due to their vast applications in optical networks, optical characterization, and optical sensing. The required device characteristics can be very different for applying the tunable lasers to various areas. We classify the tunable lasers in terms of their tuning characteristics and switching speed. Four kinds of tunable lasers are described in this paper to manifest the application-dependent device structures and performance. The applications include the use of sampled grating based lasers to form multi-wavelength laser arrays, cascaded distributed-feedback lasers for multi-gas sensors, wavelength-selectable laser arrays for fast wavelength switching sources, and short cavity lasers for fault monitoring in passive optical networks.

Photonic bandgap analysis of photonic crystal slabs with elliptical holes and their formation with laser holography

The use of elliptical photonic crystals (PhCs) simplifies the fabrication procedure and provides a wide fabrication tolerance over circular holes when PhCs are realized with holographic exposure techniques. Thus, it can increase the manufacturing yield and reduce the processing cost. We systematically analyze the photonic bandgap (PBG) maps of hexagonal PhC slabs with elliptical air-holes. Despite the reduction in the PBG for elliptical PhCs, the PBG is large enough for most applications. The variation of the midgap frequency and PBG of elliptical PhCs against fluctuation in the fabrication parameters is calculated. The results verify good tolerance to fabrication error for elliptical PhCs. The elliptical PhCs provide directional PBGs, which can be used to realize new functionalities for PhC-based circuits. We also demonstrate the use of laser holography to form submicron-scale PhCs with elliptical air-holes by using negative photoresist. PhC templates with a lattice constant of 375 nm and a high aspect ratio (>3) are demonstrated. The PhC patterns have good uniformity and high reproducibility over an area of larger than 2 cm × 2 cm.

Holographic Realization of Two-Dimensional Photonic Crystal Structures on Silicon Substrates

We successfully realize submicron-scale photonic crystals on silicon substrates with good quality by laser holography technique. The use of antireflection layers is crucial for realizing submicron photonic crystals with good uniformity over a large area.

Analysis of using femtosecond laser scanning system to impurity-induced disordering of InGaAsP quantum wells

This study is the first to demonstrate the selectivity quantum well intermixing process by using a femtosecond laser scanning-induced disordering technique. The advantages of the femtosecond laser are photochemical machining and the two-photon absorption mechanism. The femtosecond laser system can convert writing into the scan to create a nanostructure by adjusting the lens. The effect of power on the band gap shift during laser scanning was investigated. The band gap shift was small and unstable without the heating substrate. A wavelength shift higher than 77.3 nm for the InGaAsP MQW material was obtained at elevated temperatures.

Aligned silicon nanowire arrays for achieving black nonreflecting silicon surface

A new fabrication process, which includes deposition of thin silver film on silicon surface prior to wet etching, is proposed for realizing aligned silicon nanowires with high uniformity, resulting in black nonreflecting silicon surface.

Fabrication and optical properties of aligned silicon nanowire arrays realized with thin silver film

Silicon nanowire arrays realized by depositing thin silver film before etching are demonstrated to have good material and optical properties. They can provide <0.4% antireflection over >1400-nm wavelength range for large-area silicon samples.

Holographic design and realization of hexagonal 2D photonic crystal with elliptical air holes

Highly-ordered two-dimensional hexagonal photonic crystals (PhCs) with elliptical air holes are realized by low-cost laser holographic technique. PhCs of 375-nm lattice constant can be realized with good uniformity and repeatability.