There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

While the nonradiative decay of surface plasmons was once thought to be only a parasitic process that limits the performance of plasmonic devices, it has recently been shown that it can be harnessed in the form of hot electrons for use in photocatalysis, photovoltaics, and photodetectors. Unfortunately, the quantum efficiency of hot electron devices remains low due to poor electron injection and in some cases low optical absorption. Here, we demonstrate how metamaterial perfect absorbers can be used to achieve near-unity optical absorption using ultrathin plasmonic nanostructures with thicknesses of 15 nm, smaller than the hot electron diffusion length. By integrating the metamaterial with a silicon substrate, we experimentally demonstrate a broadband and omnidirectional hot electron photodetector with a photoresponsivity that is among the highest yet reported. We also show how the spectral bandwidth and polarization-sensitivity can be manipulated through engineering the geometry of the metamaterial unit ...

/pdf/metamaterial-perfect-absorber-based-hot-electron-2k7330ppvf.pdf

Metamaterial Perfect Absorber Based Hot Electron Photodetection

In the past decade graphene has been one of the most studied material for several unique and excellent properties. Due to its two dimensional nature, physical and chemical properties and ease of manipulation, graphene offers the possibility of integration with the exiting semiconductor technology for next-generation electronic and sensing devices. In this context, the understanding of the graphene/semiconductor interface is of great importance since it can constitute a versatile standalone device as well as the building-block of more advanced electronic systems. Since graphene was brought to the attention of the scientific community in 2004, the device research has been focused on the more complex graphene transistors, while the graphene/semiconductor junction, despite its importance, has started to be the subject of systematic investigation only recently. As a result, a thorough understanding of the physics and the potentialities of this device is still missing. The studies of the past few years have demonstrated that graphene can form junctions with 3D or 2D semiconducting materials which have rectifying characteristics and behave as excellent Schottky diodes. The main novelty of these devices is the tunable Schottky barrier height, a feature which makes the graphene/semiconductor junction a great platform for the study of interface transport mechanisms as well as for applications in photo-detection, high-speed communications, solar cells, chemical and biological sensing, etc. In this paper, we review the state-of-the art of the research on graphene/semiconductor junctions, the attempts towards a modeling and the most promising applications.

Graphene Schottky diodes: an experimental review of the rectifying graphene/semiconductor heterojunction

Graphene Schottky diodes: An experimental review of the rectifying graphene/semiconductor heterojunction

Due to recent breakthroughs, silicon photonics is now the most active discipline within the field of integrated optics and, at the same time, a present reality with commercial products available on the market. Silicon photodiodes are excellent detectors at visible wavelengths, but the development of high-performance photodetectors on silicon CMOS platforms at wavelengths of interest for telecommunications has remained an imperative but unaccomplished task so far. In recent years, however, a number of near-infrared all-silicon photodetectors have been proposed and demonstrated for optical interconnect and power-monitoring applications. In this paper, a review of the state of the art is presented. Devices based on mid-bandgap absorption, surface-state absorption, internal photoemission absorption and two-photon absorption are reported, their working principles elucidated and their performance discussed and compared.

Near-infrared sub-bandgap all-silicon photodetectors: State of the art and perspectives

We report vertically illuminated, resonant cavity enhanced, graphene–Si Schottky photodetectors (PDs) operating at 1550 nm. These exploit internal photoemission at the graphene–Si interface. To obtain spectral selectivity and enhance responsivity, the PDs are integrated with an optical cavity, resulting in multiple reflections at resonance, and enhanced absorption in graphene. We get a wavelength-dependent photoresponse with external (internal) responsivity ∼20 mA/W (0.25A/W). The spectral selectivity may be further tuned by varying the cavity resonant wavelength. Our devices pave the way for developing high responsivity hybrid graphene–Si free-space illuminated PDs for optical communications, coherence optical tomography, and light-radars.

Vertically Illuminated, Resonant Cavity Enhanced, Graphene–Silicon Schottky Photodetectors

Silicon-based technologies provide an ideal platform for the monolithic integration of photonics and microelectronics In this context, a variety of passive and active silicon photonic devices have been developed to operate at telecom and datacom wavelengths, at which silicon has minimal optical absorption - due to its bandgap of 112 eV Although in principle this transparency window limits the use of silicon for optical detection at wavelengths above 11 μm, in recent years tremendous advances have been made in the field of all-silicon sub-bandgap photodetectors at telecom and datacom wavelengths By taking advantage of emerging materials and novel structures, these devices are becoming competitive with the more well-established technologies, and are opening new and intriguing perspectives In this paper, a review of the state-of-the-art is presented Devices based on defect-mediated absorption, two-photon absorption and the internal photoemission effect are reported, their working principles are elucidated and their performance discussed and compared

/pdf/state-of-the-art-all-silicon-sub-bandgap-photodetectors-at-2frfv1pnnw.pdf

State‐of‐the‐art all‐silicon sub‐bandgap photodetectors at telecom and datacom wavelengths

In this letter, a near infrared all-silicon (all-Si) photodetector integrated into a silicon-on-insulator waveguide is demonstrated. The device is based on the internal photoemission effect through a metal/Si Schottky junction placed transversally to the optical field confined into the waveguide. The technological steps utilized to fabricate the device allow an efficiently monolithic integration with complementary metal-oxide semiconductor compatible structures. Preliminary results show a responsivity of 0.08 mA/W at 1550 nm with a reverse bias of 1 V and an efficient behavior both in C and L band. Finally, an estimation of bandwidth for GHz range is deduced.

Cu/p-Si Schottky barrier-based near infrared photodetector integrated with a silicon-on-insulator waveguide

Design, fabrication, and characterization of an asymmetric metal-semiconductor-metal photodetector, based on internal photoemission effect and integrated into a silicon-on-insulator waveguide, are reported. For this photodetector, a responsivity of 4.5 mA/W has been measured at 1550 nm, making it suitable for power monitoring applications. Because the absorbing metal is deposited strictly around the vertical output facet of the waveguide, a very small contact area of about 3 µm2 is obtained and a transit-time-limited bandwidth of about 1 GHz is demonstrated. Taking advantage of this small area and electrode asymmetry, a significant reduction in the dark current (2.2 nA at −21 V) is achieved. Interestingly, applying reverse voltage, the photodetector is able to tune its cut-off wavelength, extending its range of application into the MID infrared regime.

Maurizio Casalino

Papers

Near-infrared sub-bandgap all-silicon photodetectors: State of the art and perspectives

Vertically Illuminated, Resonant Cavity Enhanced, Graphene–Silicon Schottky Photodetectors

State‐of‐the‐art all‐silicon sub‐bandgap photodetectors at telecom and datacom wavelengths

Cu/p-Si Schottky barrier-based near infrared photodetector integrated with a silicon-on-insulator waveguide

Asymmetric MSM sub-bandgap all-silicon photodetector with low dark current