MBE Growth and Properties of ZnTe- and CdTe-Based Nanowires

Abstract

We review our results on the growth of ZnTe-and CdTe-based nanowires (NWs) and on their basic structural and optical properties. The nanowires were produced by using molecular beam epitaxy (MBE) with the use of a mechanism of catalytically-enhanced growth. The growth of ZnTe, CdTe, ZnMgTe and ZnMnTe nanowires was performed from elemental Zn, Cd, Mn, Mg and Te sources on the surfaces of (001)-, (110)-and (111)B-oriented GaAs substrates with Au nanocatalysts. The morphological and structural properties of the nanowires were assessed by using X-ray diffractometry, field-emission scanning electron microscopy, and high resolution transmission electron microscopy. Additional studies of the compositions of both the nanowires and the Au-rich nanocatalysts were performed with the use of energy dispersive X-ray spectroscopy. The optical properties of the NWs were assessed by using photoluminescence and Raman-scattering studies performed in both macro and micro modes. The studies revealed that binary and quaternary nanowires with average diameters from 30 to 70 nm and lengths from 1 to 2.6 µm were monocrystalline in their upper parts, their growth axis was 111 , and they grow along the [111] direction of the substrate, independent of the substrate orientation used. A Au-rich (with 20 % Ga) spherical nanocatalyst was always visible at the tip of a nanowire, thus indicating that a vapor-liquid-solid mechanism was responsible for the growth of the ZnTe-and the CdTe-based nanowires. The formation of homogeneous mixed crystal ZnMnTe and ZnMgTe nanowires was demonstrated by measurements of the variation of the lattice constant and by Raman experiments that revealed the expected shift and appearance of new phonon lines and a strong enhancement of the LO-phonon structures for an excitation close to the exciton energy of the NW materials. The photoluminescence from the internal Mn 2+ transition between crystal-field-split energy levels ( 4 T1 → 6 A1) was observed in the ZnMnTe nanowires.

ZnTe nanocrystal formation and growth control on UV-transparent substrate

“…The Raman transitions near 108, 216, 283, 323, 428, and 644 cm À1 correspond, respectively, to the normal phonon modes: (i) second order transverse acoustic (2TA) [19][20][21], (ii) first order longitudinal optical (1LO) [2,11,12,[19][20][21], (iii) second order longitudinal acoustic (2LA) [19][20][21], (iv) third order transverse/longitudinal optical coupled to the first order longitudinal acoustic (TO/LO + LA) [19,20] (v) second order longitudinal optic (2LO) [2,11,12,19,21,22], and (vi) third order longitudinal optic (3LO) [2,11]. It should be noted that this new PZABP matrix not only allows ZnTe NC growth but is also UV-transparent.…”

“…ZnTe has also attracted much attention because of its very high electro-optic coefficient and dielectric constant in the terahertz range -properties which can be advantageous as electro-optic field detectors [4,6,9,10]. Until now, ZnTe nanostructures have been synthesized by different techniques such as thermal evaporation, hot wall evaporation, radio frequency cathodic evaporation, solvothermal processes, molecular beam epitaxy [2,6,[11][12][13] and colloidal solutions [5,14]. Most of these ZnTe structures have been obtained in the form of monocrystalline nanowires [6,9] and, more recently, nanocrystals [5].…”

Raman spectroscopy of MBE‐grown ZnTe‐based nanowires

“…As it was previously shown for the Zn 1-x Mg x Te NWs, the present Raman spectra give thus another experimental proof of the replacement of a part of Zn 2+ ions by Mn 2+ ions in the crystal lattice. In the case of Zn 1-x Mn x Te NWs additional support for the substitutional incorporation of Mn into the zinc site of the lattice comes from the observation of the strong photoluminescence line centred at energies around 2 eV [9,11,[13][14][15]. Figure 8 shows a typical example of a Raman spectrum accumulated for the Zn 1-x Mn x Te NWs (in this case x = 0.30) [15].…”

“…[9,10,13,17]), while for some other data the standard laboratory diffractometer and Cu Kα radiation were applied (e.g., [12]). …”

TEM analysis of the container effect of Au‐based catalyst droplets during vapour‐liquid‐solid growth of axial ZnTe/CdTe nanowires

“…Additionally, growth of ZnTe/CdTe heterostructure NWs has been reported [13,14]. The present paper reports on the structural and chemical characterization of the interface of axial ZnTe/CdTe NWs grown by molecular beam epitaxy (MBE).…”