In the case of narrow nanowires (NWs) the surface-to-volume ratio is extremely large and surface states significantly reduce the carrier lifetime and degrade the optoelectronic device performance. Therefore, a surface passivation is of a great importance, especially for ZnTe NWs which oxidize easily. Such passivation can be achieved by forming a shell of a large band gap material around the NW so that the surface states are moved away from the charge carriers confined in the core.

Figure 1. The SEM image of a side-view of the 090110A sample.

Figure 2. The diffraction patterns of the 090110A sample: (a) symmetrical 2θ/ω scan, (b) 2θ scan in glancing incidence geometry.

Table 1. The growth and annealing parameters of the core-shell ZnTe/Zn_1-xMg_xTe nanowires.

In this report we present the results of structural characterization of the core-shell ZnTe/ Zn_1-xMg_xTe NWs grown by MBE technique on the GaAs(111) substrate. The ZnTe NWs were grown at the temperature of about 470 ºC according to the procedure described in [1]. The Zn_1-xMg_xTe shells were produced immediately after the growth of the ZnTe cores. In order to produce such shells the substrate temperature was reduced to the value which stops the axial growth of NWs and forces the radial growth of Zn_1-xMg_xTe shell. The post growth annealing has been applied for some samples. The technological parameters of the investigated samples are listed in the Table 1, and the electron scanning microscopy (SEM) image of a side-view of the 090110A sample is shown in Fig. 1

Figure 3. The part of the 2θ-ω diffraction pattern in the vicinity of the 333 NW peaks of the samples 090110A and 090110B with different time of the shell growth: (a) 10 minutes; (b) 15 minutes.

The X-ray measurements were performed using synchrotron radiation at the W1 beamline at DESY-HASYLAB. The monochromatic X-ray beam of wavelength λ = 1.54056 Å was used. Two modes of measurement were applied: symmetrical 2θ-ω scan and coplanar 2θ scan in the glancing incidence geometry [2].

The diffraction patterns measured for the sample 090110A in the symmetrical geometry (2θ-ω scan) and in the glancing incidence mode (2θ scan) are shown in Figure 2a,b. They are typical for all studied samples. It was confirmed that the crystallographic orientation of the substrate forces the orientation of NWs – three orders of reflections from (111) lattice planes from GaAs substrate and from NWs are visible in the pattern presented in Figure 2a. The measurement in the glancing incidence geometry (Fig. 2b) shows the relatively thin polycrystalline layer grown on the substrate between NWs. A zoom of the symmetrical pattern in the vicinity of 333 NW peak allows to notice its splitting (see Figs 3 and 4). This splitting indicates the monocrystalline character of the Zn_1-xMg_xTe shell with the same crystallographic orientation as that of the ZnTe core.

Figure 4. The part of the 2θ-ω diffraction pattern in the vicinity of the 333 NW peaks: (a) not annealed 092910B sample; (b) sample 092910A annealed at 450 ºC.

The second pair of the samples (092910A and 092910B) shows an influence of the post-growth annealing on the NWs structure. In the not annealed sample, 092910B, the splitting of the 333 NW peak is clearly visible (Fig. 4a), while in the annealed sample, 092910A, only small asymmetry on the left side of the peak can be noticed (Fig. 4b), which may be caused by the diffusion of Mg to the core during annealing procedure.

From the lattice parameters calculated for Zn_1-xMg_xTe shell components of the NWs their chemical composition x can be estimated as follows: x  ~= 0.11 for the samples 090110A and 090110B and x ~= 0.12 for sample 092910B. In the case of 092910A sample only average value of x can be estimated: x_average~= 0.075.

As it is visible from the Figures 3 and 4, the lattice parameters of the ZnTe cores are larger than that of the uncovered ZnTe NWs [3] – the most probable reason of such behaviour is the tensile strain of ZnTe core caused by Zn_1-xMg_xTe shell.

Acknowledgements: This work was partially supported by the European Community-Research Infrastructure Action under the FP6 "Structuring the European Research Area" Programme (through the Integrated Infrastructure Initiative "Integrating Activity on Synchrotron and Free Electron Laser Science", Contract RII3-CT-2004-506008) and the European Union within European Regional Development Fund, through grant Innovate Economy (POIG.01.01.02-00-008/08).

 References

[1] E. Janik, P. Dłużewski, S. Kret, A. Presz, H. Kirmse, W. Neumann, W. Zaleszczyk, L.T. Baczewski, A. Petroutchik, E. Dynowska, J. Sadowski, W. Caliebe, G. Karczewski, T. Wojtowicz, Nanotechnology 18 (2007) 475606

[2] E. Dynowska, W. Szuszkiewicz, J.Z. Domagała, E. Janik, M. Wiater, G. Karczewski, T. Wojtowicz, W. Caliebe, HASYLAB Annual Reports (2006) 756

[3] E. Dynowska, W. Szuszkiewicz, J.Z. Domagała, E. Janik, A. Presz, T. Wojtowicz, G. Karczewski, W. Caliebe, Radiation Physics and Chemistry 78 (2009) 120

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/24565 must be provided.

1. Defect distribution along needle-shaped PrVO₄ single crystals grown by the slow-cooling method
2. MBE grown microcavities based on selenide and telluride compounds
3. GaN substrates with variable surface miscut for laser diode applications
4. Neutron scattering studies of short-period MnTe/ZnTe superlattices: magnetic order, magnon propagation and confinement
5. X-ray diffraction studies of (Pb,Cd)Te solid solution – possible new material for thermoelectric applications
6. Hexagonal MnTe with NiAs structure: thermal expansion coefficients and exchange striction
7. 1D ZnO-based structures obtained by thermal oxidation of ZnTe and ZnTe/Zn nanowires
8. Photoreflectance study of Ga(Bi,As) and (Ga,Mn)As epitaxial layers grown under tensile and compressive strain
9. Physical properties of unique ZnO single crystals from Oława Foundry
10. Photoluminescence studies of giant Zeeman effect in MBE-grown cobalt-based dilute magnetic semiconductors
11. MBE growth, structural, magnetic, and electric properties of (In,Ga)As-(Ga,Mn)As core-shell nanowires
12. New Ca₁₀Li(VO₄)₇ laser host: growth and properties
13. Quaternary (Ga,Mn)BiAs ferromagnetic semiconductor -MBE growth, structural and magnetic properties
14. X-ray measurements of type II InAs/GaSb superlattice in a wide angular range using the P08 beamline at PETRAIII
15. Low-temperature expansion of metastable Pb_1-xCd_xTe solid solution
16. Investigation of strain and lattice parameters distribution in epitaxial laterally overgrown InGaN/GaN structures 
17. Can we control the process of room temperature ferromagnetic clusters formation in GaMnAs matrix?
18. Optimization of technology for contact metallization in electronic devices - XRD and EXAFS studies
19. Structural transformations of GaMnAs layer annealed under enhanced hydrostatic pressure
20. Surface morphology of InGaN layers
21. Zinc oxide grown by Atomic Layer Deposition - a material for novel 3D electronics
22. Dimethylzinc and diethylzinc as precursors for monocrystalline zinc oxide grown by Atomic Layer Deposition
23. Application of Ti-Al-N MAX-phase for contacts to GaN
24. Transparent p-type ZnO obtained by Ag doping
25. Raman spectroscopy of ZnTe-based nanowires grown by MBE ^*
26. Structure of Si:Mn annealed under enhanced stress conditions
27. Effect of high pressure annealing on defect structure of GaMnAs
28. Influence of high temperature annealing on the local atomic structure around Mn atoms and magnetic properties of (Ga,Mn)As layers
29. Catalytic growth by molecular beam epitaxy and properties of ZnTe-based semiconductor nanowires
30. X-ray Diffraction as a Tool of InGaN layer Characterization.
31. Structural inhomogenities in GdCa₄O(BO₃)₃ single crystals
32. Liquid phase growth and characterization of laterally overgrown GaSb epitaxial layers
33. Distribution of strain in laterally overgrown GaAs layers determined by x-ray diffraction
34. Determination of stress in composite engineered substrates for GaN-based RF power devices
35. Effect of stress on structural transformations in GaMnAs
36. Comparison of various GaSb-based device structures for application in thermophotovoltaic cells
37. Optical properties of p-type ZnO:(N, As, Sb)
38. Optical and magnetooptical properties of the p-type ZnMnO.
39. Crystalline structure and surface morphology of Dy_xO_y films grown on Si
40. Preparation and characterization of hexagonal MnTe and ZnO layers
41. p-type conducting ZnO: fabrication and characterisation
42. Fabrication and characterization of II-VI diluted magnetic p-n junctions
43. Growth and characterization of thin films of ZnO by Atomic Layer Epitaxy
44. Bowing of epitaxial structures grown on bulk GaN substrates
45. Defects in GaMnAs - influence of annealing and growth conditions
46. Use of element selective methods for characterization of thin films
47. Quantitative transmission electron microscopy investigation of localised stress in heterostructures
48. High-pressure phase transition and compressibility of zinc-blende HgZnSe mixed crystals
49. Structure characterisation of MBE-grown ZnSe:Cr layers
50. Lattice parameters changes of GaMnAs layers induced by annealing