Fabrication and characterization of ultra-fast Si-based detectors for near-infrared wavelengths

This thesis presents two different concepts for the fabrication of ultrafast metal-semiconductor-metal (MSM) photodetectors, which are to be used in the near-infrared wavelength regime and which are compatible to silicon processing techniques. To achieve this goal, we have grown Si-Si$_{1-x}$Ge$_{x}$ undulating layer superlattices with x=0.39 and 0.45 by molecular beam epitaxy (MBE) an top of epitaxial implanted COSi$_{2}$ layers and fabricated "vertical" MSM detectors. The devices show a quantum efficiency of 5% for the wavelength of 1320 nm and 0.9 % for 1550 nm. We performed time response measurements, using a Ti:sapphire laser and an optical parametric oscillator which generates ultrafast pulses at infrared wavelengths. An electrical response time of 11.6 ps füll width at half maximum (FWHM) was obtained at a wavelength of 1300 nm. At 1550 nm a response time of 9.4 ps was measured. In a second approach, we have grown pure Ge by MBE an Si(111). The sensitive volumes are 270 nm thick Ge films. Interdigitated Cr metal top electrodes of 1.5 - 3 $\mu$m spacing and identical finger width form Schottky contacts to the Ge film. These detectors show a response time of 12.5 ps füll width at half maximum both at 1300 nm and 1550 nm. The temporal response is limited by the transit time of the carriers between the electrodes

Design of a waveguide-coupled GeSn disk laser

We report on the design of a waveguide coupled GeSn microdisk-laser cavity in which the germanium virtual substrate serving as a template for GeSn growth is repurposed for the definition of passive on-chip interconnection waveguides. A main challenge resides in transferring the optical power from the upper (Si)GeSn gain stack to the underlying virtual substrate layer and is solved with laser mode engineering. Designs are based on experimentally realized layer stacks and waveguide outcoupling efficiencies as high as 27% are shown in compact resonator geometries with a small, 7 $\mu$m radius, with 42% of the power being recycled in the laser cavity

SiGeSn/GeSn hetero- and multiple quantum well structures for optoelectronics on Si

Advanced information technology has to be able to cope with the enormous amounts and rates of data requirements. New architectures of computing systems, such as neuromorphic computing, will enable deep learning and massive parallel data handling. However, it will need also large amounts of data for training as well as fast transfer rates of data between logic and storage devices. Here, advanced chip and board designs, including silicon optical interposer may allow much higher density of signal traces between co-packaged chips. In particular co-packaged silicon photonic chips allow optical interconnections between systems-in-package. Thus silicon interposer can directly contain photonic devices based on group alloys. In a long term vision this technology might be enabled by GeSn lasers permitting to connect optically individual chips within the system-in-package.In the past years significant progress has been made to develop optically active devices based on Si. A direct band gap for GeSn alloys containing more than 8.5% of Sn was demonstrated and the optically pumped GeSn laser were reported [1,2]. In order to improve the device performance and achieve electrical operation at sufficiently low power still severe challenges have to be met. The GeSn active region has to be embedded in a heterostructure providing optical waveguiding and efficient carrier injection. The active region may contain quantum well structures to warrant low threshold currents and room temperature operation. Please click Additional Files below to see the full abstract

Detrmination of the parameters of the ground state of C2H3D molecule

Present study dedicated to analysis of C2H3D molecule spectra and determination of the parameters of the ground vibrational state of the molecule. In total, positions of more than 10000 transitions were determined. 1037 ground state combination differences were used to improve ground state parameters of the molecule

Strain Engineered Electrically Pumped SiGeSn Microring Lasers on Si

SiGeSn holds great promise for enabling fully group-IV integrated photonics operating at wavelengths extending in the mid-infrared range. Here, we demonstrate an electrically pumped GeSn microring laser based on SiGeSn/GeSn heterostructures. The ring shape allows for enhanced strain relaxation, leading to enhanced optical properties, and better guiding of the carriers into the optically active region. We have engineered a partial undercut of the ring to further promote strain relaxation while maintaining adequate heat sinking. Lasing is measured up to 90 K, with a 75 K T0. Scaling of the threshold current density as the inverse of the outer circumference is linked to optical losses at the etched surface, limiting device performance. Modeling is consistent with experiments across the range of explored inner and outer radii. These results will guide additional device optimization, aiming at improving electrical injection and using stressors to increase the bandgap directness of the active material