Optoelectronics of Single Mixed Dislocations in Van Der Waals Core-Shell Nanowires

While dislocations are traditionally perceived as detrimental to electronic materials, recent theories predicted emerging functional properties associated with dislocations. To identify and ultimately harness such functionality, approaches are needed for embedding single dislocations with tunable geometry (edge/screw ratio) in small-volume host crystals. Here, we address this challenge by mixing screw- and edge-dislocations in Ge_1-xSn_xS layered (van der Waals) core-shell nanowires. Phase separation during vapor-liquid-solid growth yields the required core-shell structure, and the growth process also produces a homojunction between a defect-free layered segment near the tip and a base segment containing a single mixed (helical) dislocation. Nanometer-scale cathodoluminescence (CL) spectroscopy sheds light on the effects of single helical dislocations on optoelectronics. CL shows that the luminescence intensity depends on the distance from the dislocation line. Efficient radiative recombination is found for the pristine material near the nanowire tip whereas the dislocated part of the nanowires shows a sharp reduction of the spontaneous emission quantum efficiency, attributed to the edge component of the helical dislocation. The results demonstrate control over the geometry of single mixed dislocations and the ability of probing their effect on functional properties, important steps toward the ultimate use of dislocations as active elements in devices.