In-operando investigations of structure and function of nanowire optoelectronics

Domain topic

Nano Physics



Semiconductor nanowires (NWs) based on III-V material combinations have promising applications for light- emitting diodes, low-cost solar cells, high speed transistors, qubits, single photon sources, and other devices. Strain induced in the nanowires due to compositional variations or the necessary presence of metal contacts and oxide dielectrics can significantly affect the electronic band structure as well as induce strong internal piezoelectric fields. This can influence central properties such as the color of light emitted, recombination efficiencies and carrier mobilities both positively and negatively. One example is the wurtzite (WZ) (hexagonal) crystal structure of GaN NWs in which local deformation of the GaN unit cell leads to formation of an internal piezoelectric field. It was demonstrated that a single GaN NW exhibits stronger piezoelectricity than a bulk GaN. Integration of the NWs into an electric circuit by metallic contacts may induce additional strain and, therefore, may lead to additional piezoelectric effects in the structure. This may dramatically influence electron−hole pair recombination and alter the efficiency of optoelectronic devices based on GaN NWs. To truly understand and hence control the influence of metal contacts in a fully functioning nanodevice a direct correlation between function and structure is needed. This can be accomplished using X-ray nanodiffraction and various newly developed coherent diffraction techniques in combination with electrical and optical measurements of the behavior of the same device.

Project Description

In the frame of this project we will employ newly developed X-ray coherent scattering methods such as Bragg coherent X-ray diffractive imaging and ptychography to reveal structural changes in NWs in devices and under applied voltage in combinations with electron microscopies as well as, electrical and optical device measurements. By these studies we plan to determine strain and deformation of single nanostructures with applied voltage in-situ and in-operando with high spatial resolution and correlate this directly with their electronic and optical response as measured with high time and spatial resolution. The particular nanowire devices to be studied will be chosen for both their potential applications and the opportunity to obtain a fundamental understanding of the structure function relationship of semiconductor nanostructures as they function in real devices.

Methodological keywords

X-ray nanodiffraction, coherent X-ray diffraction imaging, optical systems, simulation start-to-end & optimization