We report on a strain-induced phase transformation in Ge nanowires under external shear stresses. The resulted polytype heterostructure may have great potential for photonics and thermoelectric applications. ⟨111⟩-oriented Ge nanowires with standard diamond structure (3C) undergo a phase transformation toward the hexagonal diamond phase referred as the 2H-allotrope. The phase transformation occurs heterogeneously on shear bands along the length of the nanowire. The structure meets the common phenomenological criteria of a martensitic phase transformation. This point is discussed to initiate an on going debate on the transformation mechanisms. The process results in unprecedented quasiperiodic heterostructures 3C/2H along the Ge nanowire. The thermal stability of those 2H domains is also studied under annealing up to 650 °C by in situ TEM.

The experiments on the dc current influence on resonant terahertz plasma wave detection in InGaAs∕InAlAs multichannel high electron mobility transistors are reported. We observed the line width shrinking when a dc current is applied. We show that this line width decrease is due to the current induced reduction of plasma wave damping and takes place because the current drives the system toward the Dyakonov-Shur plasma wave instability.