Semiconductor Nanowires: from fundamental research to innovative devices

Project leaders

Lucia Sorba, Vladimir Dubroskii

Agreement

RUSSIA - RFBR-suspended - Russian Foundation for Basic Research

Call

CNR/RFBR 2015-2017

Department

Physical sciences and technologies of matter

Thematic area

Physical sciences and technologies of matter

Status of the project

Extended

Research proposal

III-V semiconductor nanowires (NWs) are attracting increasing interest as potential building blocks for electronic and optoelectronic devices due to their nanoscale dimension. A large effort is currently under way in order to gain better control of their morphology and to assemble them in complex architectures. What makes III-V semiconductor NWs most attractive is the possibility of growing heterostructures with materials with very different lattice constants. In fact, due to the large surface/volume ratio the strain is relaxed in a few nm thick region close to the interface [1].
During the three year project, different types of heterostructured NWs will be investigated, and the experimental results obtained by the group at Institute of Nanoscience of National Research Council (NANO) will be modeled and interpreted by the theoretical group at St. Petersburg Academic University (SPAU). In the recent years, the collaboration between the two groups has been already established, and interesting results on the understanding of the growth mechanisms responsible for the growth of heterostructured InAs/InSb NWs were obtained [2,3]. Through this bilateral project we would like to continue and strengthen this activity in order to improve our understanding of the mechanisms responsible for the growth of heterostructured III-V NWs, and to have a better control on the realization of NWs with suitable morphological properties and crystal structure depending on the device application.
Recent theoretical works indicate that the crystal structure has a strong influence on the electronic and optical properties of semiconductor materials, and in particular a transition from an indirect to a direct band gap for III-V wurtzite (WZ) materials has been predicted. In contrast to bulk crystals, GaAs and GaP NWs with different crystal structures -WZ or Zinc blende (ZB)- can be obtained. However, highest ionicity crystals such as N-based semiconductor compounds show a perfect WZ crystal structure while arsenide and phosphide based NWs, due to the intermediate ionicity values, present mixed WZ-ZB crystal structures. Many and contradictory results are present in literature, and GaAs and GaP NWs with different crystal structures have been observed employing different growth techniques and different growth protocols [4,5,6]. A clear picture of the influence of the growth conditions, low or high supersaturation regime, on the crystal formation in GaP NWs and the realization of defect-free GaP NWs with well-defined crystal structure is still an open issue. This requires controlled growth, theoretical modeling and analysis which are offered by the present partnership. Direct bandgap of WZ GaP NWs will open a new region of the spectrum for optical devices, provided the morphology and crystal phase control.
Another issue that we are planning to investigate during this project is the understanding of the growth mechanisms of more complex heterostructured NWs. In particular, the morphology of GaAs/InAs and GaAs/InAs/GaAs heterostrured NWs will be investigated, and the effect of changing the catalyst alloy composition from an In-rich to a Ga-rich Au alloy will be studied. Development of the growth models will allow to realise high quality heterostructures with sharp interfaces and optimal crystal quality. This activity will have strong impact due to the wide band discontinuity between GaAs and InAs semiconductor crystals which allows the realization of highly confined low dimensional structures, potentially exhibiting quantum effects at relatively high temperatures, paving the way to non-millikelvin quantum devices.
The NANO group has a deep know-how and experience in the growth of semiconductor nanowires (NWs) by chemical beam epitaxy (CBE) and their morphological and structural characterization via electron microscopies. The crystal structure and morphology of heterostructured NWs will be investigated by the NANO group by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (SAED). Chemical determination of materials and assessment of interfaces will be pursued by Energy Selected Backscattered electrons and energy dispersive X-ray (EDX) analysis in SEM, and High Angle Annular Dark Field Scanning transmission electron microscopy and EDX analysis in TEM.
Prof. V.G. Dubrovskii, and his Laboratory of physics of nanostructures at St. Petersburg Academic University RAS, is a world leader in modeling of growth and crystal structure semiconductor NWs which is now used worldwide for the controlled synthesis of III-V NWs and sophisticated III-V NW heterostructures with predefined properties.

References

[1] D. Ercolani, F. Rossi, A. Li, S. Roddaro, V. Grillo, G. Salviati, F. Beltram and L. Sorba, "InAs/InSb nanowire heterostructures grown by chemical beam epitaxy", Nanotechnology, 20, 505605 (2009).
[2] L. Lugani, D. Ercolani, L. Sorba, N.V. Sibirev, M. A. Timofeeva, and V.G. Dubrovskii. "Modeling of InAs-InSb nanowires grown by Au-assisted chemical beam epitaxy". Nanotechnology 23, 095602 (2012).
[2] Ang Li, Nickolay V. Sibirev, Daniele Ercolani, Vladimir G. Dubrovskii, and Lucia Sorba. "Readsorption assisted growth of InAs/InSb heterostructured nanowire arrays". Cryst. Growth Des. 13, 878 (2013).
[4] M. A. Verheijen, R. E. Algra, M. T. Borgström, G. Immink, E. Sourty, Wi. J. P. van Enckevort, E. Vlieg, and E. P. A. M. Bakkers , "Three-Dimensional Morphology of GaPGaAs Nanowires Revealed by Transmission Electron Microscopy Tomography", Nanoletters 7, 3051 (2007).
[5] J.P. Boulanger and R.R. LaPierre, "Polytype formation in GaAs/GaP axial nanowire heterostructures", J. Crys. Growth 332, 21 (2011).
[6] E. Husanu, D. Ercolani, M. Gemmi and L. Sorba, "Growth of defect-free GaP nanowires",Nanotechnology 25, 205601 (2014).

Research goals

-Better understanding of the growth mechanisms for InAs/InSb and InAs/InP/InSb heterostructured NWs. Investigation of the morphology of NWs grown in different growth condition. The optimized modeling and experimental know-how will be used to change some fundamental growth parameters and to obtain controllable aspect ratio and defect-free InSb NWs for devices ranging from thermoelectric components to building blocks for spintronic devices.

-Optimization of GaAs/GaP heterostructured NWs. Experimental and theoretical investigation of the crystal phase (WZ or ZB) in GaP NWs. Theoretical investigations on the control over the crystal structure of GaP NWs by tuning the growth conditions and theoretical modeling of pure WZ GaP. Realization of defect-free GaP NWs with controlled crystal phase.


-Investigation of GaAs/InAs and GaAs/InAs/GaAs single and double heterostructured NWs. Optimization of the interface formation and the subsequent growth of good quality InAs segments. Development of the growth models to realize high quality heterostructures with sharp interfaces and optimal crystal quality. Development of theoretical studies to investigate the quarterary Au-III-V alloys such as Au-In-Ga-As, determination of chemical potentials, nucleation and growth of 2D islands, and "memory" effect. Theoretical studies of the sub-Poissonian nucleation statistics in VLS NWs and its impact on the growth interface and compositional abruptness in heterostructured NWS.

Last update: 19/04/2024