Ultra-wideband Ge-rich silicon germanium mid-infrared polarization rotator with mode hybridization flattening

Selective synthesis of germasila-adamantanes through germanium-silicon shift processes

The regioselective synthesis of germasila-adamantanes with the germanium atoms in the bridgehead positions is described starting from cyclic precursors by a cationic sila-Wagner-Meerwein (SWM) rearrangement reaction. The SWM rearrangement allows also a deliberate shift of germanium atoms from the periphery and within the cage structures into the bridgehead positions. This opens the possibility for a synthesis of germasila-adamantanes of defined germanium content and controlled regiochemistry. In the same way that sila-adamantane can be regarded as a molecular building block of elemental silicon, the germasila-adamantane molecules represent cutouts of silicon/germanium alloys.

Electrical and Structural Properties of Si1-xGex Nanowires Prepared from a Single-Source Precursor

Si_1-xGe_x nanowires (NWs) were prepared by gold-supported chemical vapor deposition (CVD) using a single-source precursor with preformed Si-Ge bonds. Besides the tamed reactivity of the precursor, the approach reduces the process parameters associated with the control of decomposition characteristics and the dosing of individual precursors. The group IV alloy NWs are single crystalline with a constant diameter along their axis. During the wire growth by low pressure CVD, an Au-containing surface layer on the NWs forms by surface diffusion from the substrate, which can be removed by a combination of oxidation and etching. The electrical properties of the Si_1-xGe_x/Au core-shell NWs are compared to the Si_1-xGe_x NWs after Au removal. Core-shell NWs show signatures of metal-like behavior, while the purely semiconducting NWs reveal typical signatures of intrinsic Si_1-xGe_x. The synthesized materials should be of high interest for applications in nano- and quantum-electronics.

Mixed-Substituted Single-Source Precursors for Si1-xGex Thin Film Deposition

A series of new mixed-substituted heteronuclear precursors with preformed Si-Ge bonds has been synthesized via a two-step synthesis protocol. The molecular sources combine convenient handling with sufficient thermal lability to provide access to group IV alloys with low carbon content. Differences in the molecule-material conversion by chemical vapor deposition (CVD) techniques are described and traced back to the molecular design. This study illustrates the possibility of tailoring the physical and chemical properties of single-source precursors for their application in the CVD of Si_1-xGe_x coatings. Moreover, partial crystallization of the Si_1-xGe_x has been achieved by Ga metal-supported CVD growth, which demonstrated the potential of the presented precursor class for the synthesis of crystalline group IV alloys.

Simulation of a High-Performance Polarization Beam Splitter Assisted by Two-Dimensional Metamaterials

It is challenging to simultaneously consider device dimension, polarization extinction ratio (PER), insertion loss (IL), and operable bandwidth (BW) to design a polarization beam splitter (PBS) that is extensively used in photonic integrated circuits. The function of a PBS is to separate polarizations of light, doubling the transmission bandwidth in optical communication systems. In this work, we report a high-performance PBS comprising two-dimensional subwavelength grating metamaterials (2D SWGMs) between slot waveguides. The 2D SWGMs exhibited biaxial permittivity by tailoring the material anisotropy. The proposed PBS showed PERs of 26.8 and 26.4 dB for TE and TM modes, respectively, and ILs of ~0.25 dB for both modes, with an unprecedented small footprint of 1.35 μm × 2.75 μm working at the wavelength λ = 1550 nm. Moreover, the present structure attained satisfactory PERs of >20 dB and ILs of <0.5 dB within an ultrabroad BW of 200 nm.

Mid-infrared polarization rotator based on a Si3N4-CaF2 hybrid plasmonic waveguide with asymmetric metal claddings

In this paper, a Si₃N₄-CaF₂ hybrid plasmonic waveguide (HPW) with an asymmetric metal cladding is designed for the mid-infrared polarization rotator (PR). The mode characteristics and polarization rotation performances of the Si₃N₄-CaF₂ HPW-based PR are simulated by using the finite element method. Operating at the wavelength of 3.5 µm, the polarization conversion efficiency between two polarization modes (PM 1 and PM 2) is larger than 99% at a Si₃N₄-CaF₂ HPW length of 104 µm. The Si₃N₄-CaF₂ HPW-based PR maintains good polarization rotation performances within fabrication tolerances from -10 to 10 nm. The polarization rotator based on the Si₃N₄-CaF₂ HPW paves the way to achieve integrated waveplates, driving many important optical functions from free space onto a chip.

SiGe quantum well infrared photodetectors on strained-silicon-on-insulator

We demonstrate p-type SiGe quantum well infrared photodetectors (QWIPs) on a strained-silicon-on-insulator (sSOI) substrate. The sSOI system allows strain-balancing between the QWIP heterostructure with an average composition of Si_0.7Ge_0.3 and the substrate, and therefore lifts restrictions to the active material thickness faced by SiGe growth on silicon or silicon-on-insulator substrates. The realized sSOI QWIPs feature a responsivity peak at detection wavelengths around 6 µm, based on a transition between heavy-hole states. The fabricated devices have been thoroughly characterized and compared to equivalent material simultaneously grown on virtual Si_0.7Ge_0.3 substrates based on graded SiGe buffers. Responsivities of up to 3.6 mA/W are achieved by the sSOI QWIPs at 77 K, demonstrating the large potential of sSOI-based devices as components for a group-IV optoelectronic platform in the mid-infrared spectral region.