The direct and indirect bandgaps of unstrained SixGe1−x−ySny and their photonic device applications

Abstract

Using empirical pseudopotential theory, the direct (Γ) and indirect bandgaps (L and X) of unstrained crystalline SixGe1−x−ySny have been calculated over the entire xy composition range. The results are presented as energy-contour maps on ternary diagrams along with a ternary plot of the predicted lattice parameters. A group of 0.2 to 0.6 eV direct-gap SiGeSn materials is found for a variety of mid-infrared photonic applications. A set of “slightly indirect” SiGeSn alloys having a direct gap at 0.8 eV (but with a smaller L-Γ separation than in Ge) have been identified. These materials will function like Ge in various telecom photonic devices. Hetero-layered SiGeSn structures are described for infrared light emitters, amplifiers, photodetectors, and modulators (free carrier or Franz-Keldysh). We have examined in detail the optimized design space for mid-infrared SiGeSn-based multiple-quantum-well laser diodes, amplifiers, photodetectors, and quantum-confined Stark effect modulators.

Imaging Structure and Composition Homogeneity of 300 mm SiGe Virtual Substrates for Advanced CMOS Applications by Scanning X-ray Diffraction Microscopy

“…3 To address the vision of a monolithically integrated light source module in a Si CMOS environment, intense research on the integration of III−V materials as well as that on band gap engineering of group IV semiconductors is applied to achieve direct band gap materials either in the form of strained Ge or SiGeSn alloy systems. 4,5 For these purposes, Germanium virtual substrates (VS) on large diameter Si wafers are considered as a central materials platform to enable these advanced technologies. Germaniumbased VS are usually obtained by exploiting the compositional grading of Si 1−x Ge x strain-relaxed buffer (SRB) layers to reduce the misfit dislocation density by gradually lowering the lattice mismatch of the heterostructure with respect to the final functional layer.…”

Growth and applications of GeSn-related group-IV semiconductor materials

“…Ge 1−x−y Si x Sn y also holds promise for energy band engineered materials such as TFETs and quantum well (QW) lasers because the energy bandgap can be controlled independently of the lattice constant by changing the relative contents of the three elements of Ge 1−x−y Si x Sn y . There have been some theoretical predictions of the energy band structure of Ge 1−x−y Si x Sn y [76][77][78][79]. Figure 7 shows a ternary diagram of the energy bandgap of Ge 1−x−y Si x Sn y with varying contents of Ge (0-100%), Si (0-100%), and α-Sn (0-100%).…”

Band engineering and growth of tensile strained Ge/(Si)GeSn heterostructures for tunnel field effect transistors

“…We expect unipolar characteristics since the tunneling probability decreases rapidly with increasing barrier height, which can reach 1eV for relaxed, Si rich SiGeSn. 8,9 Moreover, the heterostructure concept is regarded as the most scalable approach for solving the ambipolar problem. 12 In the following we demonstrate the single crystal growth of such sophisticated epitaxial stacks as suggested by the band engineering simulations.…”

“…1a. The bandgaps and band-offsets of the strained Ge on relaxed binary Ge 1-x Sn x alloys layers as well as the ternary Si y Ge 1-x-y Sn x layers have been calculated from the supercell empirical pseudopotential method 7 (the results of which have been used to find quadratic fitting expressions 8 ), together with linear interpolation of deformation potentials and band offsets of elemental Si, Ge and Sn, for x and y ranging from 0-12 at.% and 0-20 at.%, respectively. The important finding is that all GeSn y layers with y < 10, including pure Ge (y=0), grown directly on a cubic Ge 0.9 Sn 0.1 or on a partially relaxed Ge 1-x Sn x (y < x ≥ 10) undergoes the desired indirect to direct transition: the conduction band minimum shifts from the L valley to the Γ valley forming a direct bandgap at the center of the Brillouin zone.…”