Semiconductor light-emitters compatible with standard Si integration technology (SIT) are of particular interest for overcoming limitations in the operating speed of microelectronic devices. Light sources based on group IV elements would be SIT-compatible, but suffer from the poor optoelectronic properties of bulk Si and Ge. Here we demonstrate that epitaxially grown Ge quantum dots (QDs) in a defect-free Si matrix show extraordinary optical properties if partially amorphized by Ge-ion bombardment (GIB). In contrast to conventional SiGe nanostructures, these QDs exhibit dramatically shortened carrier lifetimes and negligible thermal quenching of the photoluminescence (PL) up to room temperature. Microdisk resonators with embedded GIB-QDs exhibit threshold behavior as well as a superlinear increase of the integrated PL intensity with concomitant line width narrowing as the pump power increases. These findings demonstrate light amplification by stimulated emission in a fully SIT-compatible group IV nanosystem.

Two-dimensional (2D) periodic arrays of Ge islands were realized on prepatterned Si (001) substrates by solid-source molecular-beam epitaxy. Atomic-force microscopy images demonstrate that the Ge islands are formed in the 2D laterally ordered pits of patterned substrates. The 2D periodicity of the substrate pattern is replicated throughout a stack of Ge island layers by strain-driven vertical ordering. Photoluminescence spectra of the ordered Ge islands show well-resolved peaks of the no-phonon signal and the transverse-optical phonon replica. These peaks are observed at nearly the same energy as those of random Ge islands deposited under the same conditions on unpatterned Si substrates.

Abstract:Self-assembled Ge islands were grown on stripe-patterned Si (001) substrates by solid source molecular beam epitaxy. The surface morphology obtained by atomic force microscopy (AFM) and cross-sectional transmission electron microscopy images (TEM) shows that the Ge islands are preferentially grown at the sidewalls of pure Si stripes along [-110] direction at 650 o C or along the trenches, whereas most of the Ge islands are formed on the top terrace when the patterned stripes are covered by a strained GeSi buffer layer. Reducing the growth temperature to 600 o C results in a nucleation of Ge islands both on the top terrace and at the sidewall of pure Si stripes. A qualitative analysis, based on the growth kinetics, demonstrates that the step structure of the stripes, the external strain field and the local critical wetting layer thickness for the islands formation contribute to the preferential positioning of Ge islands on the stripes. I. INTRODUCTIONSelf-assembled quantum dots (SAQD) have become an intensive research topic not only because of their promising device applications 1 but also to understand the fundamental process of strained thin film growth. A frequently employed growth mode of a strained heteroepilayer is the so-called Stranski-Krastanow(SK) mode, where after a thin wetting layer the epilayer releases the misfit strain by 3D island formation. These straightforwardly formed islands can be small and in general dislocation-free, but random in position. Although locally laterally ordered SAQD have been observed, i.e., via the growth of a multilayer of SAQD, 2,3 or the growth of SAQD above a buried strained layer with a dislocation network, 4 or growth of SAQD on a vicinal surface with step-bunching, 5,6 these kinds of short-range ordered SAQD are not adequate for most electronic or optoelectronic device applications. 1 Recently, it was shown that the combination of lithographic etching techniques and the SK growth mode provides a potential to grow long-range spatially ordered SAQD. 7-13 Some interesting phenomena have been observed during the growth of SAQD on patterned substrates. For instance InAs SAQD can be preferentially grown either on the top terraces or at the sidewalls or at the trenches of stripe-patterned GaAs substrates. 7 The number of InAs SAQD can be adjusted by the depth of patterned holes. 8 Ge SAQD are preferentially grown at the edges of selectively grown Si mesas in etched SiO 2 windows, 9,10 while they preferentially grow at the sidewalls of pure Si stripes. 11 These phenomena were discussed from the point of view of either energetics or kinetics. However, no detailed discussion about the growth of SAQD on patterned substrates has been presented so far.It is the purpose of this paper to present a description of a growth mechanism to explain the main features of the Ge island formation on stripe-patterned Si (001) substrates. The preferential positioning of Ge SAQD grown at 650 o C on patterned pure Si stripes with different periodicity and height is analyzed from AFM im...

Self-assembled Ge islands were grown by solid-source molecular-beam epitaxy on the submicron stripe-patterned Si(001) substrates at 650 °C. Atomic-force microscopy shows that the Ge islands grow preferentially at the sidewall of the Si stripes, oriented along the [−110] direction. The migration of the Ge adatoms from the top terrace down to the sidewall accounts for the island formation at the sidewall of the stripes. However, most of the Ge islands are formed on the top terraces when the patterned stripes are covered by a strained GeSi multilayer buffer prior to Ge island growth. Apparently, the strained buffer layer acts as a stressor and contributes to the preferential growth of islands on the top terrace.

In this paper, strain transfer efficiencies from a single crystalline piezoelectric lead magnesium niobate-lead titanate substrate to a GaAs semiconductor membrane bonded on top are investigated using state-of-the-art x-ray diffraction (XRD) techniques and finite-element-method (FEM) simulations. Two different bonding techniques are studied, namely, gold-thermo-compression and polymer-based SU8 bonding. Our results show a much higher strain-transfer for the “soft” SU8 bonding in comparison to the “hard” bonding via gold-thermo-compression. A comparison between the XRD results and FEM simulations allows us to explain this unexpected result with the presence of complex interface structures between the different layers.