Over the last 30 years, group-IV semiconductors have been intensely investigated in the quest for a fundamental direct bandgap semiconductor that could yield the last missing piece of the Si Photonics toolbox: a continuous-wave Si-based laser. Along this path, it has been demonstrated that the electronic band structure of the GeSn/SiGeSn heterostructures can be tuned into a direct bandgap quantum structure providing optical gain for lasing. In this paper, we present a versatile electrically pumped, continuous-wave laser emitting at a near-infrared wavelength of 2.32 µm with a low threshold current of 4 mA. It is based on a 6-periods SiGeSn/GeSn multiple quantum-well heterostructure. Operation of the micro-disk laser at liquid nitrogen temperature is possible by changing to pulsed operation and reducing the heat load. The demonstration of a continuous-wave, electrically pumped, all-group-IV laser is a major breakthrough towards a complete group-IV photonics technology platform.

The binary alloy germanium tin has already been presented as a direct group IV semiconductor at high tin concentrations and specific strain. Therefore, it offers a promising approach for the monolithic integrated light source towards the optical on-chip communication on silicon. However, the main challenge faced by many researchers is the achievement of high tin concentrations and good crystal quality. The key issues are the lattice mismatch to silicon and germanium, as well as the limited solid solubility of tin in germanium of less than 1%. Therefore, this paper presents a systematic investigation of the epitaxial growth conditions of germanium tin with tin concentrations up to 17%. For this, we performed two growth experiments utilizing molecular beam epitaxy. In one experiment, we varied the growth temperature for the epitaxy of germanium tin with 8% tin to investigate the inter-growth temperature stability. In the second experiment, we focused on the strain-relaxation of germanium tin, depending on different tin concentrations and doping types. The results of subsequent material analysis with x-ray diffraction and scanning electron microscopy allow us to narrow the epitaxial window of germanium tin. Furthermore, we present a possible explanation for the unique relaxation mechanism of germanium tin, which is significantly different from the well-known relaxation mechanism of silicon germanium.

There are vital challenges to harness the unique assets of germanium (Ge) because of Ge-on-insulator (GeOI) processing issues. The advances in molecular beam epitaxy (MBE) technology have enabled the defect-free growth of atomic-level Ge stacks over the standard monolithic silicon platform to leverage the properties of the Ge as a channel layer. Here, we present the first ever report on the authoritative integration of ferroelectric (FE) hafnium zirconium oxide (HZO) over the p-Ge/n-Ge $_{-on-}\text{n}$ -Si system. A rudimentary approach for the carrier modulation in the channel was employed using depletion approximation and negative capacitance (NC) to fabricate HZO and thin p-Ge channel-based FET. The TaN/HZO/TaN stacks were optimized and characterized for enhanced ferroelectricity and non-centrosymmetric orthorhombic phase, which is further confirmed with piezoresponse force microscopic (PFM) analysis. The trivial loop hysteresis conditions to validate the NCFET operation was discussed. The devices demonstrated a lower subthreshold swing (SS) of ~23.44 mV/dec and ${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{OFF}}$ ratio of 10 ⁵ . The threshold voltage shift ${V}_{t} = -0.6$ and −1.1 V with the body bias voltage of 0.25 and 0.5 V, respectively. Minimum DIBL measured ~26 mV/V, and rule-out gate induces drain lowering (GIDL) effect due to no gate–drain region overlap.

Due to the long spin lifetime and its optical and electrical properties, GeSn is a promising candidate for the integration of spintronics, photonics, and electronics. Here, we investigate the photoinduced inverse spin-Hall effect in a GeSn alloy with 5% Sn concentration. We generate a spin-polarized electron population at the Γ point of the GeSn conduction band by means of optical orientation, and we detect the inverse spin-Hall effect signal coming from the spin-to-charge conversion in GeSn. We study the dependence of the inverse spin-Hall signal on the kinetic energy of the spin-polarized carriers by varying the energy of the impinging photons in the $0.5–1.5\hspace{0.17em}\text{eV}$ range. We rationalize the experimental data within a diffusion model which explicitly accounts for momentum, energy, and spin relaxation of the spin-polarized hot electrons. At high photon energies, when the spin relaxation is mainly driven by phonon scattering, we extract a spin-Hall angle in GeSn which is more than ten times larger than the one of pure Ge. Moreover, the spin–charge interconversion for electrons lying at the Δ valleys of GeSn results to be $\approx 4.3$ times larger than the one for electrons at L valleys.

In this paper, a near-infrared “Ge-on-Si” camera with backside illumination, is presented. The camera consists of a photonic chip, a readout chip, and a commercial microcontroller, which is connected to a laptop via USB. The functionality of two-dimensional ( 10×10 pixels) as well as one-dimensional ( 64×1 pixel) “Ge-on-Si” pixel arrays with a pitch of 25 μm are demonstrated. The photonic chip consists of basic CMOS technology process in combination with a molecular beam epitaxy growth process. With this technology and the backside illumination a high fill-factor of 74% is achieved. Further the “Ge-on-Si” detectors are operated under zero bias operation in order to minimize the dark current and thus to maximize the signal-to-noise ratio. This enables dark currents better than 100 pA to be achieved in each pixel. A linear behavior between photocurrent and optical power of the “Ge-on-Si” detectors over a large dynamic range for optical powers between 10 ^-7 W and 10 ^-2 W is shown. With relatively thin Ge absorption layers of only 400 nm, optical responsivities of 0.36 A/W at a wavelength of 1310 nm could be achieved. The functionality of the “Ge-on-Si” camera is demonstrated by the movement of a single mode fiber over the photonic chip at a wavelength of 1310 nm.

Low-temperature magnetoresistance measurements of n- and p-doped germanium–tin (Ge _{1- y} Sn _y ) layers with Sn concentrations up to 8% show contributions arising from effects of weak localization for n-type and weak antilocalization for p-type doped samples independent of the Sn concentration. Calculations of the magnetoresistance using the Hikami–Larkin–Nagaoka model for two-dimensional transport allow us to extract the phase-coherence length for all samples as well as the spin–orbit length for the p-type doped samples. For pure Ge, we find phase-coherence lengths as long as (349.0 ± 1.4) nm and (614.0 ± 0.9) nm for n-type and p-type doped samples, respectively. The phase-coherence length decreases with increasing Sn concentration. From the spin–orbit scattering length, we determine the spin-diffusion scattering length in the range of 20–30 nm for all highly degenerate p-type doped samples irrespective of Sn concentration. These results show that Ge _{1- y} Sn _y is a promising material for future spintronic applications.