(Invited) Photoluminescence Efficiency of Germanium Dots Self-Assembled on Oxides

Abstract

Self-assembled Ge quantum dots were formed by in-situ thermal annealing of a thin amorphous Ge layer deposited by molecular beam epitaxy either on a thin porous TiO 2 layer grown on SiO 2 on Si(001) or directly on the SiO 2 layer itself. For samples with dot diameters ranging from 10 to 35 nm, the dot photoluminescence (PL) appeared primarily as a wide near-infrared band peaked near 800 meV. The peak energy of the PL band reflects the average dot size and its shape depends on the dot size distribution. Using tight binding and effective mass theoretical models, we have analyzed the PL spectrum in terms of the dot size distribution. The observed size distribution determined from transmission electron and atomic force microscopy allowed the determination of the nonlinear increase in the PL efficiency with decreasing dot diameter. Although the absolute intensities of the PL from the samples vary, the calculated efficiency curves are all well fitted by straight lines on a log-log plot, with essentially the same slope for all samples, thereby demonstrating that under the weak confinement regime investigated here there is a universal power-law increase in PL efficiency with decreasing dot size. Knowing this generic PL efficiency, we show that it is possible to evaluate the size distribution of Ge dots from their PL energy dependence.

Role of quantum confinement in luminescence efficiency of group IV nanostructures

“…Theoretical studies have suggested E G ∼ D −x , where 1 ≤ x ≤ 2 and D is the NS diameter 3,7,10 , which has been demonstrated experimentally 3,11,12 . In this work, we theoretically elucidate the dimensional dependence (D-dep) for Ge quantum dots (QDs) using experimental results reported previously by Lockwood et al 13 . We find that above D ≈ 6 nm the QDs behave like E G ∼ D −1 , below which E G ∼ D −2 .…”

Accurate electronic and optical properties of hexagonal germanium for optoelectronic applications

“…in light-emitting diodes or lasers, the k-selection rule that forbids optical dipole transitions at the minimum band gap of Ge has to be broken. To this end, ingenious approaches have been proposed, for instance, based on straining [10], nanostructuring [11,12], or amorphization [13].…”

Self-assembled inorganic nanopatterns (INPs) made by sol-gel dip-coating: Applications in nanotechnology and nanofabrication

“…Good qualitative agreement was obtained between the PLderived dot size distributions and those from AFM. Further work showed a nonlinear increase in the PL efficiency with decreasing dot diameter, suggesting that dot PL spectra used in conjunction with the theory provided a promising method to evaluate Ge dot size distributions [59]. The latter approach confirms that oxide nanoperforated surfaces with controlled motif dimension and periodicity can be used to control the size of metallic Ge nanodots formed by solid dewetting.…”