High-speed Ge-on-GaAs photodetector.

In this work, a germanium (Ge) on gallium arsenide (GaAs) photodetector is demonstrated with the optical response from 850 nm to 1600 nm, which has potential for monolithic integration with VCSELs on GaAs platform as transceiver working beyond 900 nm. The device exhibits a responsivity of 0.35A/W, 0.39 A/W and 0.11 A/W at 1000 nm, 1310 nm and 1550 nm, respectively and dark current of 8 nA at -1 V. The 10 µm diameter back-illuminated device achieves a 3-dB bandwidth of 9.3 GHz under -2 V bias. A donor-like trap at the interface between the Ge and GaAs collection layers is verified by capacitance-voltage curve and deep-level transient spectroscopy (DLTS) measurement, which impedes the depletion in GaAs collection layers.

Experimental Evidence of Superdiffusive Thermal Transport in Si0.4Ge0.6 Thin Films.

Superdiffusive thermal transport represents a unique phenomenon in heat conduction, which is characterized by a size (L) dependence of thermal conductivity (κ) in the form of κ ∝ Lß with a constant ß between 0 and 1. Although superdiffusive thermal transport has been theoretically predicted for SiGe alloys, direct experimental evidence is still lacking. Here, we report on a systematic experimental study of the thickness-dependent thermal conductivity of Si0.4Ge0.6 thin films grown by molecular beam epitaxy. The cross-plane thermal conductivity of Si0.4Ge0.6 thin films spanning a thickness range from 20 to 1120 nm was measured in the temperature range 120-320 K via a differential three-omega method. Results show that the thermal conductivity follows a consistent κ ∝ t0.26 power law with the film thickness (t) at different temperatures, providing direct experimental evidence that alloy-scattering dominated thermal transport in SiGe is superdiffusive.