L. Augel

Growth and characterization of SiGeSn quantum well photodiodes.

We report on the fabrication and electro-optical characterization of SiGeSn multi-quantum well PIN diodes. Two types of PIN diodes, in which two and four quantum wells with well and barrier thicknesses of 10 nm each are sandwiched between B- and Sb-doped Ge-regions, were fabricated as single-mesa devices, using a low-temperature fabrication process. We discuss measurements of the diode characteristics, optical responsivity and room-temperature electroluminescence and compare with theoretical predictions from band structure calculations.

Ge-on-Si PIN-photodetectors with Al nanoantennas: The effect of nanoantenna size on light scattering into waveguide modes

Metallic nanoantennas can be used to enhance the efficiency of optical device operation by re-distributing electromagnetic energy. Here, we investigate the effect of a random distribution of disc-shaped Al nanoantennas of different diameters deposited on Ge-on-Si PIN-photodetectors on the wavelength-dependent responsivity. We compare our experimental results to simulations and find that the largest responsivity enhancement is obtained for wavelengths that correspond to energies at or below the bandgap energy of Ge. We argue that this is the result of antenna-mediated scattering of light into waveguide modes within the Ge-on-Si PIN-photodetectors, which is effectively influenced by nanoantenna size, and we discuss a possible application of the concept for integrated biosensing.

The Zener-Emitter: A novel superluminescent Ge optical waveguide-amplifier with 4.7 dB gain at 92 mA based on free-carrier modulation by direct Zener tunneling monolithically integrated on Si

We report on the first experimental demonstration of a monolithic integrated Group-IV Ge semiconductor optical amplifier (SOA) — the Ge Zener-Emitter (ZE). The ZE is a device featuring light amplification up to 4.7 dB (92 mA) at center wavelength of 1700 nm and gain-bandwidth of 98 nm on Si (100). Our novel direct Zener band-to-band tunneling (BTBT) injection method enables low-voltage electron emission beyond the Boltzmann-limit (38 mV/dec at 1.55 K, 88 mV/dec at 300 K), achieving population-inversion at 0.45 V (41 mA). The ZE possesses a Si-Ge-Si hetero-structure with excellent CMOS integration compatibility by planar device design (550 nm) and an ultra-thin (100 nm) Ge virtual substrate (VS) on Si (100). Moreover, the ZE shows superior light emission properties with pulsed lasing at 1667 nm and superluminescent LED characteristic (150 cm−1 max. gain at 270 K, 100 cm−1 max. gain at 300 k). The developed ZE device presents a promising feature to monolithic Si-photonics filling the gap for energy-efficient light emission and amplification in a small footprint (1 mm) integrated waveguide-amplifier.

Contact resistivities of antimony-doped n-type Ge1−x Sn x

As Ge1−x Sn x is being investigated for CMOS applications, obtaining contacts to n-type Ge1−x Sn x with low specific contact resistivity (ρ c) is a major concern. Here, we present results on specific contact resistivities of Sb doped n-type Ge1−x Sn x with 0 ≤ x ≤ 0.08 also with varying doping concentrations using Ni, Ag and Mn as contact metals. Our results show that Ni offers the lowest ρ c for all x values of Ge1−x Sn x . The lowest ρ c measured for Ni contacts on highly n-doped Ge0.92Sn0.08 is 2.29 × 10−6 Ω cm2. We find a strong dependence of the specific contact resistivity on doping, which we attribute to the fact that strong Fermi level pinning is present in metal/n-Ge1−x Sn x contacts.

Plasmonic nanohole arrays on Si-Ge heterostructures: an approach for integrated biosensors

Nanohole array surface plasmon resonance (SPR) sensors offer a promising platform for high-throughput label-free biosensing. Integrating nanohole arrays with group-IV semiconductor photodetectors could enable low-cost and disposable biosensors compatible to Si-based complementary metal oxide semiconductor (CMOS) technology that can be combined with integrated circuitry for continuous monitoring of biosamples and fast sensor data processing. Such an integrated biosensor could be realized by structuring a nanohole array in the contact metal layer of a photodetector. We used Fouriertransform infrared spectroscopy to investigate nanohole arrays in a 100 nm Al film deposited on top of a vertical Si-Ge photodiode structure grown by molecular beam epitaxy (MBE). We find that the presence of a protein bilayer, constitute of protein AG and Immunoglobulin G (IgG), leads to a wavelength-dependent absorptance enhancement of ~ 8 %.

Optofluidic sensor system with Ge PIN photodetector for CMOS-compatible sensing

Vertical optofluidic biosensors based on refractive index sensing promise highest sensitivities at smallest area footprint. Nevertheless, when it comes to large-scale fabrication and application of such sensors, cheap and robust platforms for sample preparation and supply are needed—not to mention the expected ease of use in application. We present an optofluidic sensor system using a cyclic olefin copolymer microfluidic chip as carrier and feeding supply for a complementary metal–oxide–semiconductor compatibly fabricated Ge PIN photodetector. Whereas typically only passive components of a sensor are located within the microfluidic channel, here the active device is directly exposed to the fluid, enabling top-illumination. The capability for detecting different refractive indices was verified by different fluids with subsequent recording of the optical responsivity. All components excel in their capability to be transferred to large-scale fabrication and further integration of microfluidic and sensing systems. The photodetector itself is intended to serve as a platform for further sophisticated collinear sensing approaches.

Ellipsometric characterization of doped Ge 0.95 Sn 0.05 films in the infrared range for plasmonic applications.

GeSn as a group-IV material opens up new possibilities for realizing photonic device concepts in Si-compatible fabrication processes. Here we present results of the ellipsometric characterization of highly p- and n-type doped Ge0.95Sn0.05 alloys deposited on Si substrates investigated in the wavelength range from 1 to 16 μm. We discuss the suitability of these films for integrated plasmonic applications in the infrared region.

Plasmonics-integrated Ge PIN-photodetectors: efficiency enhancement by Al nanoantennas and plasmon detection

The aim of integrating plasmonic functionality with photonic devices is twofold: on the one hand, plasmonic nanoantennas can enhance the functionality of photonic devices and enable their miniaturization. On the other hand, photonic devices can be a part of plasmonic transmission lines and act e.g. as plasmon detectors. Here, we present results on both aspects in a CMOS-compatible device setup using Ge PIN-photodetectors and Al nanostructures. Plasmonic nanoantennas are metallic nanostructures that enable the control and manipulation of optical energy in the visible and near-infrared spectrum and have been proposed as a means to enhance absorption and quantum yields for photovoltaics, to increase spatial resolution for optical microscopes and to enhance the energy efficiency of light-emitting devices. We present experimental results on the enhancement of Ge PIN-photodetector efficiency by Al nanoantennas. In order to investigate plasmon waveguiding and detection, metal grating structures and metal-insulator-metal slot waveguides were fabricated by electron beam lithography in the Al metallization layer of Ge PIN-photodetectors. Photocurrent maps of the devices under local illumination show that plasmons can be optically excited at the grating and are then guided by the slot waveguide towards the Ge PIN-photodetector where they are detected as photocurrent. Using Ge PIN-photodetectors and Al nanostructures as a CMOS-compatible device setup, we show how plasmonic nanostructures can be used for efficiency enhancement of photonic devices and discuss plasmon detection with Ge PIN-photodetectors with possible applications.

Si)GeSn plasmonics

Plasmonic nanostructures serve to enhance light-matter interaction at the nanoscale. Metallic nanoantennas in conjunction with group-IV-devices can be used to enhance the efficiency of scaled-down devices [1] or to develop concepts for integrated biosensing [2]. However, for applications at wavelengths in the near-IR and mid-IR range, metals suffer from high Drude damping as a result of the high charge carrier concentration present in these materials [3]. At these wavelengths, highly doped semiconductors can potentially outperform metals as materials for plasmonic antennas. Compared to Ge, GeSn has a lower conductivity effective mass and, thus, can be used to extend the wavelength range for plasmonic applications to the 5–10 μm region [4].

Ge PIN photodetectors with nanohole arrays for refractive index sensing

We present an experimental realization of an integrated biosensor consisting of a Ge PIN photodetector with an Al nanohole array in its contact metal layer. The device responsivity strongly depends on the surrounding refractive index, making the device suitable for integrated sensing at reduced size.