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Catalytic growth by molecular beam epitaxy and properties of ZnTe-based semiconductor nanowires

Tomasz Wojtowicz ¹, Elżbieta Janik ¹, Wojciech Zaleszczyk ¹, Janusz Sadowski ¹, Grzegorz Karczewski ¹, Piotr Dłużewski ¹, Sławomir Kret ¹, Wojciech Szuszkiewicz ¹, Elzbieta Dynowska ¹, Jaroslaw Domagala ¹, Marta Aleszkiewicz ¹, Lech T. Baczewski ¹, Alexei Petroutchik ¹, Adam M. Presz ², Wojciech Pacuski ³, Andrzej Golnik ³, Piotr Kossacki ³, Holm Kirmse ⁴, Jean F. Morhange ⁵, Wolfgang Caliebe ⁶

1. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
2. Polish Academy of Sciences, Institute of High Pressure Physics (UNIPRESS), Sokolowska 29/37, Warszawa 01-142, Poland
3. Warsaw University, Faculty of Physics, Hoża 69, Warszawa 00-681, Poland
4. Humboldt-Universität, Newtonstr. 15, Berlin 12489, Germany
5. Universite Pierre et Marie Curie, Place Jussieu, Bat F Boite 39, Paris 75252, France
6. Hamburger Synchrotronstrahlungslabor HASYLAB (HASYLAB), Notkestrasse 85, Hamburg D-22603, Germany

Abstract

We review our results on the growth of ZnTe-based nanowires (NWs) and on their basic structural and optical properties. The nanowires were produced by molecular beam epitaxy (MBE) with the use of mechanism of catalytically enhanced growth. Semiconductor nanowires have attracted considerable attention recently as very versatile nanoscale building blocks for the assembly of electronic and optoelectronic devices. Nanowires based on ZnTe can play particularly important role in the bottom-up approach to nanoelectronics due to the ease of p-type nitrogen doping of this semiconductor. Additionally magnetic atoms (e.g. Mn) can also be easily incorporated into ZnTe host, the successful growth of ZnTe-based nanowires opens new perspectives for applications in prototype nanospintronic devices, that would take advantage of spin of carriers, in addition to or instead of their charge.

The growth of ZnTe, ZnMgTe and ZnMnTe nanowires was performed from elemental Zn, Mn, Mg and Te sources on the surface of (001), (110) and (111)B oriented GaAs substrates with Au nanocatalysers. Gold nanoparticles were formed by in-situ thermal reorganization of thin layers (from 0.3 to 2 nm) of gold deposited from electron gun source in a separate MBE chamber. The catalytic growth was optimised by varying the Zn/Te flux ratio, substrate temperature and annealing of Au-layers.

The growth of nanowires was observed in-situ by reflection high energy electron diffraction and their morphology and structural properties were assessed by field-emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (TEM), and atomic force microscopy (AFM). Additional studies of the composition of both nanowires and the Au-rich nanocatalysers were performed with the use of energy dispersive X-ray spectroscopy (EDX). Optical properties of NWs were assessed by photoluminescence and Raman scattering studies performed in both macro and micro regime.

Our studies revealed that nanowires with an average diameter of about 40 nm and length above 1μm are mono-crystalline in their upper parts, their growth axis is <111>, and they grow along <111> directions of the substrate, independent of the substrate orientation. Au-rich (with 20% of Ga) spherical nanocatalyser was always visible at the tip of a nanowire, thus indicating that vapour-liquid-solid mechanism is responsible for the growth of ZnTe-based nanowires. Analysis of the length vs. diameter of the NWs points to the large contribution of the addatoms diffusing along the NWs surface to the growth rate.

This research was partially supported by the Ministry of Science and Higher Education (Poland) through grant N507 030 31/0735 and by the Network "New materials and sensors for optoelectronics, information technology, energetics and medicine".

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