Effects of annealing temperature on shape transformation and optical properties of germanium quantum dots

doi:10.1088/1674-1056/24/2/028103

Abstract The influences of thermal annealing on the structural and optical features of radio frequency (rf) magnetron sputtered self-assembled Ge quantum dots (QDs) on Si (100) are investigated. Preferentially oriented structures of Ge along the (220) and (111) directions together with peak shift and reduced strain (4.9% to 2.7%) due to post-annealing at 650 ℃ are discerned from x-ray differaction (XRD) measurement. Atomic force microscopy (AFM) images for both pre-annealed and post-annealed (650 ℃) samples reveal pyramidal-shaped QDs (density ～ 0.26×10¹¹ cm^-2) and dome-shape morphologies with relatively high density ～ 0.92 ×10¹¹ cm^-2, respectively. This shape transformation is attributed to the mechanism of inter-diffusion of Si in Ge interfacial intermixing and strain non-uniformity. The annealing temperature assisted QDs structural evolution is explained using the theory of nucleation and growth kinetics where free energy minimization plays a pivotal role. The observed red-shift ～ 0.05 eV in addition to the narrowing of the photoluminescence peaks results from thermal annealing, and is related to the effect of quantum confinement. Furthermore, the appearance of a blue-violet emission peak is ascribed to the recombination of the localized electrons in the Ge-QDs/SiO₂ or GeO_x and holes in the ground state of Ge dots. Raman spectra of both samples exhibit an intense Ge-Ge optical phonon mode which shifts towards higher frequency compared with those of the bulk counterpart. An experimental Raman profile is fitted to the models of phonon confinement and size distribution combined with phonon confinement to estimate the mean dot sizes. A correlation between thermal annealing and modifications of the structural and optical behavior of Ge QDs is established. Tunable growth of Ge QDs with superior properties suitable for optoelectronic applications is demonstrated.

Keywords: Ge QDs sputtering surface morphology optical properties

Received: 22 June 2014
Revised: 07 August 2014
Accepted manuscript online:

PACS:	81.10.Pq	(Growth in vacuum)
	78.67.Hc	(Quantum dots)
	81.16.Dn	(Self-assembly)

Fund: Project supported by Ibnu Sina Institute for Fundamental Science Study, Universiti Teknologi Malaysia through Vote Q.J130000.2526.02H94, O5 and Postdoctoral Research Grant.

Corresponding Authors: Alireza Samavati
E-mail: alireza.samavati@yahoo.com

Cite this article:

Alireza Samavati, Z. Othaman, S. K. Ghoshal, M. K. Mustafa Effects of annealing temperature on shape transformation and optical properties of germanium quantum dots 2015 Chin. Phys. B 24 028103

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Effects of annealing temperature on shape transformation and optical properties of germanium quantum dots

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