Santhad Chuwongin

Flexible photonic-crystal Fano filters based on transferred semiconductor nanomembranes

Crystalline semiconductor nanomembranes (NMs), which are transferable, stackable, bondable and manufacturable, offer unprecedented opportunities for unique and novel device applications. We report and review here nanophotonic devices based on stacked semiconductor NMs that were built on Si, glass and flexible PET substrates. Photonic-crystal Fano resonance based surface-normal optical filters and broadband reflectors have been demonstrated with unique angle and polarization properties. Such a low temperature NM stacking process can lead to a paradigm shift on silicon photonic integration and inorganic flexible photonics.

Broadband Membrane Reflectors on Glass

We report here high-performance broadband membrane reflectors based on crystalline silicon nanomembrane photonic crystals. A modified polydimethylsiloxane stamp transfer technique is developed for transferring large-area silicon membranes to glass substrates. Polarization-independent broad reflectivity at 1550-nm wavelength band was obtained from Si membrane reflectors, on both silicon and glass substrates. The experimental results also agree well with simulation results.

Design of Fano Broadband Reflectors on SOI

We report here the design of Fano resonance broadband reflectors based on two-dimensional photonic crystals on silicon-on-insulator. The impact of vertical confinements and buffer configurations was investigated with a three-dimensional finite-difference time-domain technique. Spectral red- and blue-shifts were obtained by controlling the effective buffer layer indices, with very good agreement between experimental and simulation results.

Resonance control of membrane reflectors with effective index engineering

We report here broadband membrane reflectors based on Fano resonances in patterned silicon nanomembranes. Resonance control of the reflectors was realized either by partially removing buried oxide layer underneath the device layer or by controlled SiO2 film deposition on top of the devices. Both blueshifts and redshifts were demonstrated with a turning range of 50 nm for a center wavelength of 1550 nm. These results demonstrate practical postprocess means for Fano resonance engineering for both narrowband filters and ultracompact broadband reflectors.

Design of Photonic Crystal Membrane-Reflector-Based VCSELs

We present here the cavity design of distributed-Bragg-reflector-free ultracompact Fano-resonance photonic crystal membrane-reflector vertical-cavity surface-emitting lasers on silicon, which consists of a III-V quantum-well active region sandwiched in between two single-layer Si membrane reflectors (MRs). The Si reflectors are designed to have peak reflection band around 1550 nm, with over 300-nm reflection band. The complete laser cavity resonance was determined, with considerations of unique phase and field distribution characteristics associated with these single-layer MRs. The confinement factor of the lasing mode is optimized around 6%, which enables low threshold lasing.

Polarization- and angle-dependent characteristics in two dimensional photonic crystal membrane reflectors

We report here measured angle- and polarization-dependent reflection properties in two-dimensional photonic crystal broadband membrane reflectors. Polarization independent reflection was obtained at surface normal direction. High reflection can also be obtained for one transverse electric (TE) polarization state over a wide range of incident angles. With the target of 1550 nm spectral band, the measured spectral bandwidths for TE polarization with reflectivity greater than 90% are 180 nm and 56 nm at surface normal and oblique incidence of 45°, respectively. The experimental spectrum approximates the theoretical spectral response of this membrane reflector.

Semiconductor nanomembranes for stacked and flexible photonics

Crystalline semiconductor nanomembranes (NMs), which are transferable, stackable, bondable and manufacturable, offer unprecedented opportunities for unique and novel device applications. We report here nanophotonic devices based on stacked semiconductor NMs on Si, glass and flexible PET substrates. Photonic crystal Fano resonance-based surface-normal optical filters and broadband reflectors have been demonstrated with unique angle and polarization properties. Flexible photodetectors and solar cells have also been developed based on the NM stacking processes. Such NM stacking process can lead to a paradigm shift on silicon photonic integration and inorganic flexible photonics.

Semiconductor nanomembranes for integrated and flexible photonics

Crystalline semiconductor nanomembranes (NMs), which are transferable, stackable, bondable and manufacturable, offer unprecedented opportunities for unique and novel device applications. We review here nanophotonic devices based on stacked semiconductor NMs on Si, glass and flexible PET substrates. Photonic crystal Fano resonance-based surface-normal optical filters and broadband reflectors have been demonstrated with unique angle and polarization properties. Flexible photodetectors and solar cells have also been developed based on the NM stacking processes. Such NM stacking process can lead to a paradigm shift on silicon photonic integration and hybrid organic/inorganic flexible photonics.

Nanoscale silver-assisted wet etching of crystalline silicon for anti-reflection surface textures.

We report here an electro-less metal-assisted chemical etching (MacEtch) process as light management surface-texturing technique for single crystalline Si photovoltaics. Random Silver nanostructures were formed on top of the Si surface based on the thin film evaporation and annealing process. Significant reflection reduction was obtained from the fabricated Si sample, with approximately 2% reflection over a wide spectra range (300 to 1050 nm). The work demonstrates the potential of MacEtch process for anti-reflection surface texture fabrication of large area, high efficiency, and low cost thin film solar cell.

Ag-assisted electrochemical etching of silicon for antireflection in large area crystalline thin film photovoltaics

We report here an electroless metal (Ag) - assisted chemical etching (MacEtch) process as light management surface-texturing technique for ultra-thin single crystalline Si thin film photovoltaics. Monolayer Ag nanostructures were formed on the top of the Si surface based on thin film evaporation and annealing process. Large area thin film black Si sample was obtained with simple wet etching process, with ~2% reflection over a wide spectra range (300 to 1050 nm). The work demonstrates the potential of MacEtch process for the fabrication of large area, flexible, high efficiency, and low cost thin film solar cells.