Strain profile, electronic band structure and optical gain of self-assembled Ge quantum dots on SiGe virtual substrate (original) (raw)
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We study self-assembled GeSn/SiSn quantum dots for optoelectronic application in the Silicon photonics domain. Valence force field and k.p methods are used to investigate the strain distribution and band structure with size effect. The compatibility of group IV elements with Si CMOS fabrication technology has enabled us to integrate both optical and electronic components onto a single microchip providing faster optical data transfer both between and within microchips. Quantum Dot (QD) based optoelectronic devices could be a key enabler in this domain of research. In this paper, we study one such possible structure - self assembled Ge0.5Sn0.5 QDs embedded on Si0.5Sn0.5 substrate/cap with wetting layer. Valence force field (VFF) method using Keating potential is employed to estimate its strain profile followed by electronic band structure calculation using 8 band k∙p method taking the Γ valley into consideration. The QD size effect on the fundamental transition energy is studied for optoelectronic device design.
Infrared absorption and admittance spectroscopy of Ge quantum dots on a strained SiGe layer
Semiconductor Science and Technology, 2011
A combined infrared absorption and admittance spectroscopy is carried out in examining the energy level structure and the hole emission process in self-assembled Ge quantum dots (QDs) placed on a strained Si 0.65 Ge 0.35 quantum well (QW), which, in turn, is incorporated in a Si matrix. In the midinfrared spectral range, the dots exhibit three dominant absorption bands peaked at 130, 250 and 390 meV. By a comparison between absorption measurements and six-band k · p calculations, the long-wave (∼130 meV) resonance is attributed to a transition from the QD hole ground state to the two-dimensional heavy-hole states confined in the Si 0.65 Ge 0.35 layer. The mid-wave absorption band around 390 meV is ascribed to a transition from the QD hole ground state to the three-dimensional continuum states of the Si matrix. An equivalent absorption cross section for these two types of transitions is determined to be 1.2 × 10 −15 cm 2 and 1.2 × 10 −16 cm 2 , respectively. The origin of the transmission minimum around 250 meV is more ambiguous. We tentatively propose that it can be due to transition either from the highest heavy-hole subband of the Si 0.65 Ge 0.35 QW to continuum states above the Si barrier or from the dot states to the light-hole and split-off subbands of the Si 0.65 Ge 0.35 layer. The photoinduced bleaching of the near-infrared absorption is detected under interband optical excitation of undoped samples. This finding is explained by blocking the interband transitions inside the dots due to the state filling effect. By using the admittance spectroscopy, the mechanism of hole escape from QDs in the presence of an ac vertical electric field is identified. A thermally activated emission from the QD ground state into the two-dimensional states of the Si 0.65 Ge 0.35 well is observed. From the temperature-and frequency-dependent measurements the QD hole ground state is determined to be located ∼160 meV below the heavy-hole subband of the Si 0.65 Ge 0.35 layer in good agreement with the results obtained by infrared absorption spectroscopy and six-band k · p theory. The information acquired from our experimental observations is valuable for feasible device applications.
CLEO/Pacific Rim 2003. The 5th Pacific Rim Conference on Lasers and Electro-Optics (IEEE Cat. No.03TH8671), 2003
Photoluminescence investigations on stacked Ge/Si quantum dots with dirferent thicknesses of Si spacer layer arepresented. According to the emission energy shiji in the Ge dots, we found that thinner spacer will lead to remarkable Ge-Si intermixing. Such intermixing can be attributed to the strain-induced material intermixing, which tends to shallow the dot potential, soflen the dot/spacer interface sharpness, and hence degrade their room-temperature emission properties. The thickness of Si spacer inserted between Ge quantum dot (QD) multi-layers play a decisive role in the strain distribution in multiple stacked Ge/Si QDs. Since the global strain energy has to be minimized, partial strain will be relaxed from the buried Ge dots into the Si spacer, depending on the spacer thickness [l]. Such
MBE growth of vertically ordered Ge quantum dots on Si
physica status solidi (c), 2007
The in plane lattice constant of the silicon film on germanium is shown to alter as the film grows; the changes reflect the process of strains relaxation of that result from the misfit of the Ge and Si lattice constants. The thickness allowing detection of changes in the in plane lattice constant of the Si film during the growth on the Ge surface depends on the germanium layer thickness. The thickness of the silicon film where elastic relaxation is determined as dependent on the germanium layer thickness. TEM studies indicate the vertical ordering of the germanium island layers when the thickness of the Si layer in between Ge layers is not sufficient to provide the full strain relaxation. The vertical ordering of Ge islands in the multilayer structure results in a decrease in the island density at reduced dispersion of their shape and size.
Optical study of strained double Ge/Si quantum dot layers
IOP Conference Series: Materials Science and Engineering, 2009
In this work we studied experimentally and theoretically the emission from Ge WL and QDs. The numerical calculations give a prediction for the energy positions of the WL and QDs related emissions in accordance with the PL measurements. The experimental results show an independence of the energy position of the WL related emission of the interaction between the two deposited Ge layers whereas a shift to higher energies was observed for the dots related emission with the increase of the Si spacer thickness. Two different transitions (A and B) related to QDs were identified. The temperature dependence of the intensity was investigated. No dependence of the activation energies on the Si spacer thickness was observed.