Heterogeneously grown tunable group-IV laser on silicon

Abstract

Tunable tensile-strained germanium (epsilon-Ge) thin films on GaAs and heterogeneously integrated on silicon (Si) have been demonstrated using graded III-V buffer architectures grown by molecular beam epitaxy (MBE). epsilon-Ge epilayers with tunable strain from 0% to 1.95% on GaAs and 0% to 1.11% on Si were realized utilizing MBE. The detailed structural, morphological, band alignment and optical properties of these highly tensile-strained Ge materials were characterized to establish a pathway for wavelength-tunable laser emission from 1.55 μm to 2.1 μm. High-resolution X-ray analysis confirmed pseudomorphic epsilon-Ge epitaxy in which the amount of strain varied linearly as a function of indium alloy composition in the InxGa1-xAs buffer. Cross-sectional transmission electron microscopic analysis demonstrated a sharp heterointerface between the epsilon-Ge and the InxGa1-xAs layer and confirmed the strain state of the epsilon-Ge epilayer. Lowtemperature micro-photoluminescence measurements confirmed both direct and indirect bandgap radiative recombination between the Γ and L valleys of Ge to the light-hole valence band, with L-lh bandgaps of 0.68 eV and 0.65 eV demonstrated for the 0.82% and 1.11% epsilon-Ge on Si, respectively. The highly epsilon-Ge exhibited a direct bandgap, and wavelength-tunable emission was observed for all samples on both GaAs and Si. Successful heterogeneous integration of tunable epsilon-Ge quantum wells on Si paves the way for the implementation of monolithic heterogeneous devices on Si

Design, Theoretical, and Experimental Investigation of Tensile-Strained Germanium Quantum-Well Laser Structure

“…Once the strain amount inside the Ge is above 1.5%, the L-valley and -valley are at the same conduction band minimum (see Fig. 1b), and hence the material is direct bandgap, as reported by our earlier work 31,35,[38][39][40] and by others. 27,55,56 Beyond the tensile strained amount of 1.5%, the optical transition must be from the conduction band at the -valley to LH or HH.…”

“…As we have showcased in Figure 7, the need for direct bandgap Ge for light sources via strain engineering, we have experimentally demonstrated the tunable tensile strained epitaxial ε-Ge layers in the strain ranges from 0.0% to 1.95% 31,35,[38][39][40] on GaAs and Si substrates using InGaAs strain template as well as 1.6% and 1.95% strained InGaAs/ε-Ge/InGaAs QW structures on linearly graded InxGa1-xAs metamorphic buffer using solid source MBE. These structures were characterized using different analytical tools 31,35,[38][39][40] to access the materials quality. In this aspect, the defect analysis using plan-view transmission electron microscopy (PV-TEM) is indispensable since the defects can cause the losses in the ε-Ge lasing media, as shown in Figure 7b.…”

“…The room-temperature optical properties using photoluminescence (PL) spectroscopy, materials analysis, and Ge laser modeling using FIMMWAVE were demonstrated as a first step toward the development of Ge-based light sources. Therefore, our monolithic heterogeneous integration of a tunable wavelength Ge laser structure (via strain and band gap engineering) on GaAs and ultimately the transfer of the process to a Si substrate using an InGa­(Al)­As/III–V buffer architecture ,− would provide a paradigm shift for photonic technology on Si.…”

Quantum efficiency enhancement of germanium-on-insulator photodetectors for integrated photonics on silicon

“…The Area 1< Area 2< Area 3. .......... 41 Figure 16 (a) Responsivity of waveguide-integrated photodetectors from earlier reports as a function of their Ge waveguide length; The electromagnetic field profiles of the waveguide-coupling configurations of (b) butt coupling and (d) evanescent coupling [38] are shown in (c) and (e) [43], respectively; Carrier-drift configurations (using p-i-n structure as an example): (d) lateral and (e) vertical [38] [48] and (c) grating [47] structures for a higher QE of Ge A summary of some Ge tensile-straining approaches for an integrated laser: Substrate undercut for (a) uniaxial-strained nanowire [68] and (b) biaxialstrained membrane [71]; (c) Ge hetero-epitaxy on InGaAs/InAlAs buffer layers [74]; SiNx stressors with (d) top [75] and (e) all-around [81] configurations. .... 51 Strain contour plots of GeSn fins with SiNx liner stressor (b) without [5,6] and (c) with [3] the substrate undercut.…”

“…Figure 22 A summary of some Ge tensile-straining approaches for an integrated laser: Substrate undercut for (a) uniaxial-strained nanowire [68] and (b) biaxial-strained membrane [71]; (c) Ge hetero-epitaxy on InGaAs/InAlAs buffer layers [74]; SiNx stressors with (d) top [75] and (e) all-around [81] configurations.…”