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Title: Ulrich Pietsch: Structure-to-property relations of single semiconductor core-shell nanowires probed by X-ray nano-diffraction and cathodoluminescence
Number: 3/20
Status: Closing date exceeded
Begin: Thursday, 16.01. 2020, 14:00
Tutor: Václav Holý, Milan Dopita
Location: Lecture room F2, Facutly of Mathematics and Physics, First floor Ke Karlovu 5, Prague 2

nanocent


Nano Seminar

 

Thursday, 16. 1. 2020, 14.00,

Lecture room F2 (1st floor), MFF UK, Ke Karlovu 5

 

Ulrich Pietsch

Department of Physics, Univerity of Siegen, Siegen, Germany

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Structure-to-property relations of single semiconductor core-shell nanowires probed by X-ray nano-diffraction and cathodoluminescence

Introduction/Purpose
III-V semiconductor nanowires (NWs) grow mainly in the cubic zincblende (ZB) and/or the hexagonal wurtzite (WZ) phases. However, besides stacking faults and ZB twin planes, more complex stacking sequences may occur. Particularly, the intermediate 4H phase or extended segments of alternating ZB and WZ stacking (mixed, or M phase) can be observed. Multi-shell heterostructures for tailored light emission adopt the crystal structure of the NW core. The particular real structure may differ among individual nanowires grown on the same substrate and thus the respective physical properties may vary.

Methods
Here, we demonstrate the direct correlation between the structural and optical properties of several single core-multi-shell GaAs/In0.15Ga0.85As/GaAs/AlAs/GaAs nanowires grown by molecular beam epitaxy onto the same pre-patterned 111 Si substrate. On the as-grown nanowires, the structural phase composition was revealed by synchrotron-beam-assisted X-ray nano-diffraction [1] monitoring of the axial variation of the 111 Bragg-reflection intensity. The optical properties of the same NWs were extracted by home-lab, low-temperature cathodoluminescence (CL) measurements.

Results
Comparing these properties, we reveal a correlation between both the emission energy as well as intensity and the particular structural phase within the nanowires. In particular, we found that the optical yield at the axial position of the 4H/M phase is enhanced up to a factor of about 80 in comparison to the WZ and ZB polytypes. Furthermore, we show that the real structure of the NWs can be influenced by the nano-XRD experiment. Systematic studies as function of the absorbed X-ray dose reveal an upper threshold above which the real structure of the NWs is modified and the optical properties degrade.

Conclusions
We demonstrated the correlation between spatial distribution of NW phase structure and the local optical properties along the NW growth axis. Both quantities are changing among different NWs grown on the same sample.

Selected references
[1] Ali AlHassan et al.,Complete structural and strain analysis of single GaAs/(In,Ga)As/GaAs core-shell-shell nanowires by means of in-plane and out-of-plane x-ray nano -diffraction, J Appl. Cryst (2018). 51, 1387-1395. https://doi.org/10.1107/S1600576718011287