Nathan Youngblood

Waveguide-integrated black phosphorus photodetector with high responsivity and low dark current

A gated multilayer black phosphorus photodetector integrated on a silicon photonic waveguide operating in the telecom band is demonstrated with intrinsic responsivity up to 135 mA W−1 and 657 mA W−1 in 11.5-nm- and 100-nm-thick devices, respectively.

Multifunctional Graphene Optical Modulator and Photodetector Integrated on Silicon Waveguides

Graphenes unique optoelectronic properties have been exploited for many photonic applications. Here, we demonstrate a single graphene-based device that simultaneously provides efficient optical modulation and photodetection. The graphene device is integrated on a silicon waveguide and is tunable with a graphene gate to achieve a near-infrared photodetection responsivity of 57 mA/W and modulation depth of 64% with GHz bandwidth. Simultaneous modulation of photocurrent and optical transmission has been achieved, which may lead to unprecedented optoelectronic applications.

Three-Dimensional Integration of Black Phosphorus Photodetector with Silicon Photonics and Nanoplasmonics

We demonstrate the integration of a black phosphorus photodetector in a hybrid, three-dimensional architecture of silicon photonics and metallic nanoplasmonics structures. This integration approach combines the advantages of the low propagation loss of silicon waveguides, high-field confinement of a plasmonic nanogap, and the narrow bandgap of black phosphorus to achieve high responsivity for detection of telecom-band, near-infrared light. Benefiting from an ultrashort channel (∼60 nm) and near-field enhancement enabled by the nanogap structure, the photodetector shows an intrinsic responsivity as high as 10 A/W afforded by internal gain mechanisms, and a 3 dB roll-off frequency of 150 MHz. This device demonstrates a promising approach for on-chip integration of three distinctive photonic systems, which, as a generic platform, may lead to future nanophotonic applications for biosensing, nonlinear optics, and optical signal processing.

Integration of 2D materials on a silicon photonics platform for optoelectronics applications

Abstract Owing to enormous growth in both data storage and the demand for high-performance computing, there has been a major effort to integrate telecom networks on-chip. Silicon photonics is an ideal candidate, thanks to the maturity and economics of current CMOS processes in addition to the desirable optical properties of silicon in the near IR. The basics of optical communication require the ability to generate, modulate, and detect light, which is not currently possible with silicon alone. Growing germanium or III/V materials on silicon is technically challenging due to the mismatch between lattice constants and thermal properties. One proposed solution is to use two-dimensional materials, which have covalent bonds in-plane, but are held together by van der Waals forces out of plane. These materials have many unique electrical and optical properties and can be transferred to an arbitrary substrate without lattice matching requirements. This article reviews recent progress toward the integration of 2D materials on a silicon photonics platform for optoelectronic applications.

Ultrafast photocurrent measurements of a black phosphorus photodetector

With its high mobility, narrow bandgap, and unique anisotropy, black phosphorus (BP) is a promising material for optoelectronic applications. Waveguide-integrated photodetectors with RC-limited speeds up to 3 GHz have been recently demonstrated at telecom wavelengths. To truly be competitive, however, BP photodetectors must reach speeds of tens of GHz. Here, we use BPs nonlinear photoresponse to measure the intrinsic speed of a BP photodetector using ultrafast pump-probe measurements. With this technique, we are able to observe how the detection speed depends on both the incident power and applied source-drain bias. A minimum response time of 60 ps was observed which corresponds to an intrinsic bandwidth of 9 GHz.

Midinfrared Electro-optic Modulation in Few-Layer Black Phosphorus

Black phosphorus stands out from the family of two-dimensional materials as a semiconductor with a direct, layer-dependent bandgap spanning the visible to mid-infrared (mid-IR) spectral range. It is, therefore, a very promising material for various optoelectronic applications, particularly in the important mid-IR range. While mid-IR technology has been advancing rapidly, both photodetection and electro-optic modulation in the mid-IR rely on narrow-band compound semiconductors, which are difficult and expensive to integrate with the ubiquitous silicon photonics. For mid-IR photodetection, black phosphorus has already been proven to be a viable alternative. Here, we demonstrate electro-optic modulation of mid-IR absorption in few-layer black phosphorus. Our experimental and theoretical results find that, within the doping range obtainable in our samples, the quantum confined Franz-Keldysh effect is the dominant mechanism of electro-optic modulation. A spectroscopic study on samples with varying thicknesses reveals strong layer dependence in the interband transition between specific pairs of sub-bands. Our results show that black phosphorus is a very promising material to realizing efficient mid-IR modulators.

Black phosphorus photodetector on silicon photonic and plasmonic hybrid platform

Silicon photonics, plasmonic structures and two dimensional material are integrated vertically on SOI (Silicon on Insulator) substrate to produce a short channel photodetector. Its estimated average intrinsic responsivity is 220 mA/W.

Mid-infrared electro-optic modulation in few-layer black phosphorus (Conference Presentation)

Black phosphorus stands out from the family of two-dimensional materials as a semiconductor with a direct, layer-dependent bandgap in energy corresponding to the spectral range from the visible to the mid-infrared (mid-IR), as well as many other attractive optoelectronic attributes. It is, therefore, a very promising material for various optoelectronic applications, particularly in the important mid-IR range. While mid-IR technology has been advancing rapidly, both photodetection and electro-optic modulation in the mid-IR rely on narrow-band compound semiconductors, which are difficult and expensive to integrate with the ubiquitous silicon photonics. For mid-IR photodetection, black phosphorus has been proven to be a viable alternative. Here, we demonstrate electro-optic modulation of mid-IR absorption in few-layer black phosphorus under field applied by an electrostatic gate. Our experimental and theoretical results find that, within the doping range obtainable in our samples, the quantum confined Franz-Keldysh effect is the dominant mechanism of electro-optic modulation. Spectroscopic study on samples with varying thickness reveals strong layer-dependence in the inter-band transition between different sub-bands. Our results show black phosphorus is a very promising material to realizing efficient mid-IR modulators.

Mid-infrared electro-optic modulation in black phosphorus

An out of plane electric field can modulate the optical absorption of black phosphorus due to a combination of Pauli blocking and quantum-confined Franz-Keldysh effects. Optical transitions between different sub-bands are explored and over 5% modulation is demonstrated in 13 nm black phosphorus.

Study of black phosphorus anisotropy on silicon photonic waveguide

Due to its unique crystal structure, black phosphorus (BP) shows anisotropic electric and optical properties. In this work, we demonstrate its optical anisotropy by measuring its different absorptions of TE and TM modes travelling in silicon photonic waveguides. In the experiment, when BP crystal armchair axis is aligned perpendicularly to waveguide, the measured absorption coefficients for TE and TM are 0.821 dB/μm and 0.413 dB/μm, respectively. The result matches well with our calculated absorptions of 1.075 dB/μm and 0.581 dB/μm for TE and TM modes. By carefully selecting BP thickness and orientation, it is possible to selectively absorb either TE or TM mode and as an example, TE/TM contrast can reach up to 1.1 dB/μm when BP thickness is 100 nm.