Nanometre-scale germanium photodetector enhanced by a near-infrared dipole antenna

Abstract

A critical challenge for the convergence of optics and electronics is that the micrometre scale of optics is significantly larger than the nanometre scale of modern electronic devices. In the conversion from photons to electrons by photodetectors, this size incompatibility often leads to substantial penalties in power dissipation, area, latency and noise [1][2][3][4] . A photodetector can be made smaller by using a subwavelength active region; however, this can result in very low responsivity because of the diffraction limit of the light. Here we exploit the idea of a half-wave Hertz dipole antenna (length 380 nm) from radio waves, but at near-infrared wavelengths (length 1.3 mm), to concentrate radiation into a nanometre-scale germanium photodetector. This gives a polarization contrast of a factor of 20 in the resulting photocurrent in the subwavelength germanium element, which has an active volume of 0.00072 mm 3 , a size that is two orders of magnitude smaller than previously demonstrated detectors at such wavelengths.The interaction of light with nanostructured metals has been studied extensively in recent years [5][6][7][8][9][10] . The resulting near-field optical intensity can be two to three orders of magnitude higher than the incident intensity. However, very little research has been carried out into the interaction of these strong near fields with semiconductors and the further transformation of the optical energy into electricity [11][12][13] . It has recently been demonstrated that the photogeneration of carriers in silicon can be enhanced by a surface-plasmon antenna at a wavelength of 840 nm (ref. 12). This method has the practical limitation that the entire grating structure necessary for exciting a surface-plasmon resonance occupies a large area in terms of wavelengths. Alternatively, a C-shaped aperture has been used to enhance photodetection locally without exciting long-range surface-plasmon resonances 13 . However, for easy integration and high-speed, low-capacitance operation, it is generally advantageous to design planar devices such as the metal -semiconductor-metal (MSM) detectors that are widely used in high-speed optical receivers 14 .Resonant antennas can confine strong optical near fields in a subwavelength volume, as demonstrated recently for bow-tie antennas and dipole antennas at visible wavelengths using the resulting scattered light 15,16 . The optical properties of the structures largely depend on the size and shape of the antennas.

Device engineering for silicon photonics

“…A new type of germanium APD structure integrated on SOI reported recently has a smaller footprint, lower bias voltage and lower noise [44]. Th ere are also eff orts to combine novel components into the device structure, such as dipole antennas in order to enhance the performance of integrated germanium photodetectors [45].…”

Electromagnetic Spin Current Density of Surface Plasmon Polaritons

“…In recent years, with current progress in a wealth of electromagnetic simulation methods and the state-of-the-art nano fabrication technologies, such as electron beam lithography [2], molecular beam epitaxy [3], and focussed ion beam [4], researches of various mechanisms and applications of SPPs have become increasingly intensive in a large number of fields [5,6]. Surface plasmonics involves a variety of topics relevant to optics, photonics, electronics and many other interdisciplines, e.g., artificial metamaterials [7], surface-enhanced Raman scattering [8,9], modern sensors [10], nanophotonic devices [11][12][13], and subwavelength optics [14].…”

Integrated colloidal quantum dot photodetectors with color-tunable plasmonic nanofocusing lenses

“…17,18 Dipole antennas have been demonstrated to enhance the optical cross sections of Ge nanophotodetectors. 19 Of particular practical interest is the use of a plasmonic bull's eye structure (BES), that is, a concentric plasmonic grating surrounding a nanohole aperture, 20,21 as such a structure can capture light from a large area and concentrate it into a nanoscale aperture. Extraordinary optical transmission has been demonstrated in these structures as a result of the efficient coupling of incident photons into surface plasmon polaritons, which are guided towards the center of the BES and constructively interfere in the aperture, resulting in high transmission efficiencies.…”