Analysis of the 3D distribution of stacked self-assembled quantum dots by electron tomography
- PDF / 599,542 Bytes
- 6 Pages / 595.28 x 793.7 pts Page_size
- 51 Downloads / 139 Views
NANO EXPRESS
Open Access
Analysis of the 3D distribution of stacked selfassembled quantum dots by electron tomography Jesús Hernández-Saz1*, Miriam Herrera1, Diego Alonso-Álvarez2 and Sergio I Molina1
Abstract The 3D distribution of self-assembled stacked quantum dots (QDs) is a key parameter to obtain the highest performance in a variety of optoelectronic devices. In this work, we have measured this distribution in 3D using a combined procedure of needle-shaped specimen preparation and electron tomography. We show that conventional 2D measurements of the distribution of QDs are not reliable, and only 3D analysis allows an accurate correlation between the growth design and the structural characteristics. Keywords: Focused ion beam, Electron tomography, Needle-shaped samples, Quantum dots, Semiconductor, transmission electron microscopy, High angle annular dark field PACS: 81.05.Ea, 81.07.Ta, 68.37.Ma
Background Most optoelectronic devices based in quantum dots (QDs) such as optical amplifiers [1], infrared detectors [2], or lasers [3] require stacking of multiple QDs layers to enhance properties as the number of photons emitted or absorbed per unit area. For small spacer layers, QDs tend to align vertically because of the strain fields caused by the buried dots [4,5]. These strain fields have a strong effect in the size and shape of the QDs and consequently, in the optoelectronic properties of the corresponding devices [6-11]. The vertical distribution of the QDs has a direct effect in its electronic structure due to a possible electron tunneling between layers [12], and it has also been found to influence optical properties such as the photoluminescence emission of the structure [13]. Because of this, understanding the 3D distribution of stacked QDs is essential to understand and optimize the functional properties of a wide range of devices. Although various techniques have been used to assess the vertical distribution of QDs [14-16], one of the most * Correspondence: [email protected] 1 INNANOMAT Group, Departamento de Ciencia de los Materiales e I.M. y Q.I., Facultad de Ciencias, Universidad de Cádiz, Campus Río San Pedro, s/n, Puerto Real, Cadiz 11510, Spain Full list of author information is available at the end of the article
powerful techniques for this purpose is transmission electron microscopy (TEM) because it gives direct evidence of the location of the QDs. However, the vertical alignment of the stacking of QDs is often analyzed by TEM from 2D projections of the volume of the sample in one or several directions [17,18], losing 3D information and therefore, making the complete correlation with the optical characteristics unfeasible. To solve this problem, electron tomography is the most appropriate technique. An accurate 3D reconstruction in electron tomography needs the accomplishment of some requirements, the most important one being that the input 2D images must be the true projections of the original 3D object [19]. This condition can be met by using highangle annular dark field (HAADF) scan
Data Loading...
