We report the first experimental demonstration of electrical spin injection, transport and detection in bulk germanium (Ge). The non-local magnetoresistance in n-type Ge is observable up to 225K. Our results indicate that the spin relaxation rate in the n-type Ge is closely related to the momentum scattering rate, which is consistent with the predicted Elliot-Yafet spin relaxation mechanism for Ge. The bias dependence of the nonlocal magnetoresistance and the spin lifetime in n-type Ge is also investigated. a these authors contributed equally to this work

We compared the temperature dependence of spin lifetime in n-Ge characterized from three-terminal (3T) and four-terminal (4T) Hanle measurements using single-crystalline Fe/MgO/n-Ge tunnel junctions. The bias conditions of the two schemes were chosen to be about the same in order to compare the spin lifetimes (τ 3T and τ 4T ). The temperature dependences of τ 3T and τ 4T behave in a very similar way at the low temperature region (T 10 K), and both τ 3T and τ 4T decrease as the temperature increases, which is consistent with the dominating Elliot-Yafet spin relaxation mechanism in bulk Ge. However, when the temperature is higher than 10 K, τ 4T is longer than τ 3T , which may be explained by the fact that 3T Hanle measurements are more easily affected by additional scattering effects caused by the accompanied charge current and electric field in the 3T geometry.

In chiral ferromagnets, weak spin-orbit interactions twists the ferromagnetic order into spirals leading to helical order. We investigate an extended Ginzburg-Landau theory of such systems where the helical order is destabilized in favour of crystalline phases. These crystalline phases are based on periodic arrangements of double-twist cylinders and are strongly reminiscent of blue phases in liquid crystals. We discuss the relevance of such blue phases for the phase diagram of the chiral ferromagnet MnSi.

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.

Refractive index sensing is a highly sensitive and label-free detection method for molecular binding events. Commercial implementations of biosensing concepts based on plasmon resonances typically require significant external instrumentation such as microscopes and spectrometers. Few concepts exist that are based on direct integration of plasmonic nanostructures with optoelectronic devices for on-chip integration. Here, we present a CMOS-compatible refractive index sensor consisting of a Ge heterostructure PIN diode in combination with a plasmonic nanohole array structured directly into the diode Al contact metallization. In our devices, the photocurrent can be used to detect surface refractive index changes under simple top illumination and without the aid of signal amplification circuitry. Our devices exhibit large sensitivities > 1000 nm per refractive index unit in bulk refractive index sensing and could serve as prototypes to leverage the cost-effectiveness of the CMOS platform for ultra-compact, low-cost biosensors.