Weiquan Yang

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.

Large-area InP-based crystalline nanomembrane flexible photodetectors

Large-area (3x3 mm(2)) flexible photodetectors were realized, based on crystalline InP semiconductor nanomembranes transferred to flexible polyethylene terephthalate substrates. Very low dark curre ...

Polarization-independent drop filters based on photonic crystal self-collimation ring resonators.

We report here a polarization-independent drop filter (PIDF) based on a photonic crystal self-collimation ring resonator (SCRR). Despite of the large birefringence associated with the polarization-dependent dispersion properties, we demonstrate a PIDF based on multiple-beam interference theory and polarization peak matching (PPM) technique. The PIDF performance was also investigated based on finite-difference time-domain (FDTD) technique, with excellent agreement between the theory and the simulation. For the designed drop wavelength of 1550 nm, the polarization-independent free spectral range is about 36.1 nm, which covers the whole optical communication C-band window. The proposed PIDFs are highly desirable for applications in photonic integrated circuits (PICs).

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.

Flexible solar cells based on stacked crystalline semiconductor nanomembranes on plastic substrates

We report here experimental demonstration of flexible solar cells based on crystalline semiconductor nanomembranes (NMs) transferred onto flexible PET (polyethylene terephthalate) substrates. For 1 micrometer thick p-i-n InP NMs, we obtained an open circuit voltage of 0.68 V and power efficiency of 1.5% from the photovoltaic solar cells. The results agree very well with the anticipated thin film InP solar cell performance considering the low absorption in very thin InP NMs. The efficiency remains unchanged for bending radii greater than 42 mm. It drops to 50% of its original value at a bending radius of 32 mm. The results demonstrate a promising future for such a new type of cost effective flexible thin film solar cells, based on crystalline semiconductor membranes.

Flexible crystalline InP nanomembrane LED arrays

This paper reports on flexible crystalline InP nanomembrane LED arrays with transferred InGaAsP/InP QW structure on plastic PET substrate. Two types of QW heterostructures have been designed, with total cavity thickness of one λ (wavelength). The PL peak locations are around 1527 nm. An InGaAs etch stop/sacrificial layer was used for the release of top InGaAsP QW active region. Different structures were formed based on InGaAsP QW NM transfer process. The flexible InP LED devices show excellent electrical and optical performance with low turn-on voltage, low series resistance, and the spherical optical beam profile. We also analyzed the InP LED light beam by using beam profilers. Beam profiles of flexible crystalline InP LED array without bending was investigated at room temperature whereas the driving current is 0.31 mA . Similarly, the same device with bending also was measured when the driving current is 0.36 mA.. The beam profile of device without bending is almost elliptical in shape whereas that of bending device is not elliptical.

Crystalline silicon nanomembrane stacking for large-area flexible photodetectors

Flexible photodetectors were demonstrated experimentally on large-area crystalline silicon nanomembranes (3 mmx3 mm), based on wet transfer and metal-frame supported transfer processes. Very low dark current (a few nA) and linear photoresponses were demonstrated for both Si MSM and InP PIN photodiodes on flexible PET substrates.

Electrical properties of stacking electrodes for flexible crystalline semiconductor photonic devices

We report here electrical properties of low-temperature-stacked electrodes for large-area flexible photonic devices, based on single-crystalline InP nanomembrane (NM) transfer and stacking processes. Au, Al and ITO electrodes were investigated. An excellent ohmic contact was demonstrated on the stacked InP NM?ITO electrode, with a measured contact resistivity of 0.45 ? cm2. Two types of flexible InP solar cells were also fabricated and characterized, based on the stacked InP NM?ITO and InP NM?Al contacts, respectively. The efficiency of solar cells with ITO as back contact is five times higher than that with Al as back contact. Such low-temperature energy-efficient NM transfer and electrode-stacking techniques can be applied to a wide range of flexible thin film photonic devices.

Spectral selective absorption enhancement from stacked ultra-thin InGaAs/Si Fano resonance membranes

We report here modified absorption property of InGaAs nano-membrane on a Fano filter made of patterned single crystalline silicon nano-membrane transferred onto glass substrate. Placement of an ultra-thin InGaAs film on Si Fano resonant membrane enhances the absorption with simulated enhancement factor ~35 and measured enhancement factor of ~26. Leaky modes in the photonic crystal (PC) consist of high field standing waves that can be coupled to the out of plane radiation mode provided by lattice matching of the PC. We will present simulation, device fabrication and experimental characterization of stacked ultra-thin InGaAs/Si Fano resonance membrane in the IR regime.