Influence of Sn and Cr Doping on Morphology and Luminescence of Thermally Grown Ga₂O₃ Nanowires

Abstract

Elongated micro-and nanostructures of Sn doped or Sn and Cr codoped monoclinic gallium oxide have been grown by a thermal method. The presence of Sn during growth has been shown to strongly influence the morphology of the resulting structures, including Sn doped branched wires, whips, and needles. Subsequent codoping with Cr is achieved through thermal diffusion for photonic purposes. The formation mechanism of the branched structures has been studied by transmission electron microscopy (TEM). Epitaxial growth has been demonstrated in some cases, revealed by a very high quality interface between the central rod and the branches of the structures, while in other cases, formation of extended defects such as twins has been observed in the interface region. The influence of dopants on the energy levels of Ga and O within the structures has been studied by XPS. Micro-Raman spectroscopy was used to assess the influence of Sn doping, and Sn−Cr codoping, on the vibrational properties of single nanowires. Cathodoluminescence (CL) measurements show a Sn-related complex band in the Sn-doped structures. Temperature-dependent and excitation-density-dependent CL indicates that this is a thermally activated emission. In the Sn− Cr codoped samples, the characteristic, very intense Cr 3+ red luminescence emission quenches the bands observed in the Sndoped samples. Branched, Sn−Cr codoped structures were studied with microphotoluminescence imaging and spectroscopy, and waveguiding behavior was observed along the trunks and branches of these structures.

Influence of Li doping on the morphology and luminescence of Ga2O3microrods grown by a vapor-solid method

“…On the other hand, the UV-blue band is redshifted from about 366 nm to some 400 nm and broadened when temperature increases. A similar behaviour of this band was observed for Sn, Cr, codoped gallium oxide nanostructures [9]. The sharp infrared peak keeps a similar width and shows only a slight redshift of about 2 nm.…”

“…transversal pyramids that grow on the lateral sides of the main rods. It has been previously reported that during vapour-solid (VS) growth the presence of different doping elements in the precursors can result in notable morphological changes, such as the formation of branches [9], crossing wires [17] and complex hierarchical structures [18]. However, these morphological pyramidal features have not been observed with other dopants or in undoped gallium oxide microstructures grown under similar conditions, as shown in figure 1(e).…”

“…Besides, a higher intensity of the 652 cm -1 peak with respect to the one at 658 cm -1 is observed. In previous reports, it was an indication of the presence of dopants [9]. Due to the low atomic number of Li, it is not possible to detect this element by energy dispersive X-ray spectroscopy (EDS) in SEM.…”

“…This value is similar to that obtained in Sn doped Ga2O3 [20] and expected for this type of oxide. The influence of Li on the luminescence properties of Ga2O3 is also of high interest as this oxide presents strong luminescence in different regions of the UV-vis-IR range, which can be used for different photonic applications [7][8][9][11][12]. Figure 4(a) shows the CL room temperature emission from the Li doped microrods (solid line), along with the spectrum in the same conditions of the undoped reference sample (dashed line).…”

“…However, it usually becomes a challenge and several techniques, such as in-situ doping during growth, or post growth doping by ion implantation or diffusion, have been proposed [13]. We have successfully doped Ga2O3 nanowires with several impurities, including transition metal and rare earth ions, so far by these techniques [7][8][9].…”