In-situ pulsed laser interference patterning for quantum dot site controlThursday (25.06.2020) 13:30 - 13:50 Room 2
Semiconductor self assembled quantum dots (QDs) offer a wealth of novel physics and application potential in electronics and photonics1. Epitaxial self-assembly, via the Stranski–Krastanov growth instability can create high densities of defect free QDs of dimensions on the nanometer scale. However, a limitation of the self-assembly process is the location at random sites with an inhomogeneous distribution of dot sizes. The arrangement into precise arrays and increased QD homogeneity is crucial for future quantum applications and this requires controlled nucleation on surface topological features. The nucleation of QDs onto nanoholes produced by E-beam lithography and surface etch has been extensively-studied2. However, an in-situ patterning process which directly controls nucleation during QD formation would be highly attractive. Recently, it has been shown that the application of laser interference3,4 can pattern the epitaxial surface and achieve controlled nucleation. In this work we refine these methods and examine the underlying mechanisms.
We report on the formation of highly ordered arrays of InAs quantum dots using in-situ laser interference during MBE growth. The work is performed within a chamber adapted for in-situ laser lithography. Four beam single-pulse laser interference at 355nm is applied to the growing wafer and is observed to create a dense 2D array of nanoislands positioned at the interference minima with a period of 300 nm, as shown in Fig.1 (a)-(d). The images come from the same sample and show variations in pattern shape and size due to a weak Moiré effect. We attribute the formation of the islands to surface atomic diffusion driven by the intensive photothermal gradients set up by the interference pulse. As shown in Fig.1(d) the smaller nanoislands act as preferential nucleation sites for InAs QDs. and result in site occupation dependent on the size of nanoislands and the InAs coverage. Well-organized arrays of QDs have been obtained by optimizing the laser interference parameters and the growth conditions, as shown in Fig.2. The results show a promising route capable of producing dense arrays of nanostructures in a fast and efficient way without external pre-patterning
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