Self‐Aligned Nanolenses with Multilayered Ge/SiO₂ Core/Shell Structures on Si (001)

Abstract

Silicon has been the dominant semiconductor for electronic devices for more than three decades. However, there is now a growing need to integrate electronic components with optoelectronics for telecommunications and connections between computers. Electro-optical devices, such as light-emitting diodes, vertical-cavity surface-emitting lasers, and photodetectors based on combinations of III-V semiconductor structures with conjugated silicon substrates have been demonstrated.[1-4] Although III-V semiconductors provide high coupling efficiency and low loss in fiber-optical communications, incorporating them in the well-established Si technology is difficult and expensive. It is therefore desirable to grow the active materials directly on a Si substrate.Owing to their having a narrower bandgap than Si, Si 1-x Ge x /Si heterostructures are used to fabricate optical devices that extend the range of applications of Si technology. Si-Ge/Si superlattices, quantum wells, and Ge quantum dots (QDs) have been used in modulators and photodetectors. [5][6][7][8][9][10][11][12][13][14] Both experimental and theoretical investigations, including pyramid-shaped Si-Ge superlattice QDs, [15] Ge-island resonant-cavity-enhanced detectors, [16] photonic-band engineering in opals by growth of Si/Ge multilayer shells, [17] epitaxial growth of Ge nanowires on Si substrates, [18,19] tensile epitaxial Ge films on Si substrates, and relaxed Si-Ge/Si quantum well structures, [20,21] have been actively pursued.In the present study, taking advantage of the comparably low etching rate and uniform size of self-assembled Ge-QD multilayers, a method was developed to fabricate multilayered Ge/SiO 2 core/shell nanostructures with a lenticular shape (Ge@SiO 2 nanolenses) with excellent uniformity over a large area. The fabrication process is compatible with Si/Si-Gebased integrated-circuit technology. [14,22,23] The multilayered Ge@SiO 2 nanolenses exhibited an emission at between 1.5 and 1.55 lm in their photoluminescence (PL) spectrum, and an increase of about 77 % in reflectivity in their reflectance spectrum around 1.5 lm over conventional self-assembled Ge-QD multilayers. Figure 1a is a cross-sectional transmission electron microscopy (XTEM) image depicting the as-prepared self-assembled Ge-QD multilayer structure on Si (001). The as-grown samples consisted of 10 periods of 13.1 eq-ML Ge layers (eq-ML= equivalent monolayer) followed by a 20 nm thick Si-spacer layer. In this geometry, strain fields of underlying Ge islands penetrated into the Si-spacer layer, creating a strain-energy modulation at the surface, and inducing stacks of vertically aligned, and laterally more homogeneous, islands in the upper layers.[24] As the number of multilayers increased, the dot-size uniformity improved, and the average dot size increased. This gradual increase in size within QD multilayers can be attributed to the reduction of the wetting-layer thickness in the upper layers caused by the local strain fields. It was evident that the Ge islands were well aligned fo...

The ripples and nanoparticles on silicon irradiated by femtosecond laser

“…However, with the increase of the pulse number, photomechanical fragmentation [32] should happen in the irradiated region due to the incubate effect [31], therefore, the debris increases with the increasing pulse number. The as-formed nanoparticles can be potentially applied as nanolens in nano-optics [33,34].…”

The Compositional Distribution of Ge Islands Grown by Ultra-High Vacuum Chemical Vapor Deposition

“…Recently, the growth and characterization of selfassembled Ge islands on Si have been intensively investigated for the next generation of Si-based optoelectronic devices [1]. However, the structural and optical properties of Ge islands strongly depend on growth conditions.…”

Modified growth of Ge quantum dots using C2H4 mediation by ultra-high vacuum chemical vapor deposition

“…Recently, the growth of self-assembled Ge quantum dots (QDs) on Si substrates has been intensively investigated for the next generation of Si-based optoelectronic devices [1][2][3]. Deposition of Ge onto Si(0 0 1) leads to a strain-induced spontaneous formation of the three-dimensional islands as soon as the Ge epilayer exceeds a critical thickness of 3-4 monolayers, which is the well-known Stranski-Krastanow (S-K) growth mode [4,5].…”