Tensile Strained Germanium Microstructures: A Comprehensive Analysis of Thermo‐Opto‐Mechanical Properties

Abstract

The influence of the thermomechanical effects on the optical properties of germanium microstructures is investigated. Finite element method (FEM) calculations allow a complete spatial assessment of mechanical deformations induced by a silicon nitride (SiN) stressor layer deposited on Ge micropillars. Simulated strain maps are confirmed by experimental maps obtained by Raman spectroscopy. The theoretical investigation on strain‐dependent band structure, including the presence of a strain gradient along the longitudinal direction, is exploited to fully capture photoluminescence spectroscopy experiments. Finally, the joint effect of temperature and strain on the fundamental bandgap is also quantified.

The Interplay between Strain, Sn Content, and Temperature on Spatially Dependent Bandgap in Ge1−xSnx Microdisks

“…This lets us to conclude that the strain is not impacting α and β but only the E g (0) parameter, as we previously observed for pure Ge. [14] The energy shift due to strain can be calculated analytically, [51,52] and confirms the measured value for a measured difference in strain of 0.28%. [46] estimations of E g at 300 K with the value calculated from the analysis reported in the text for the thickest samples of all the available concentrations in Table 1.…”

“…The mechanical deformation is evaluated according to Hooke's law [14] in a 3D description to offer a complete overview of all the strain field components.…”

“…The low-energy part is broadened with respect to the theoretical fit, as a result of limited band filling, indicating a low carrier injection regime, [37] or alloy broadening and strain inhomogeneity caused by the misfit dislocations at heterointerface, [38] or localized states extending in the bandgap to form an Urbach tail, [39] or also Γ-L recombination. [14] Moreover, especially for small microdisks, the lowenergy tail may be influenced by the spatially dependent radiative recombination. As explained in ref.…”

“…As explained in ref. [14], the excess carrier diffusion length is of the order of μm and the recombination rate may be stronger at the periphery of the disks, where the bandgap is smaller.…”

“…[10,11] Furthermore, mechanical deformations combined with tuned Sn content allow to control of both valence and conduction band edges and enhance carrier mobility [12] and direct optical emission. [13][14][15] The development and improvement in the performance of Ge 1Àx Sn x -based lasers was obtained by acting on strain and Sn content since the first proof-of-principle in 2015 [16] and reaching operating temperature of 130 K, [12] 180 K, [17] and 230 K [18] for both continuous-wave and pulsing modes of optically pumped lasers, with the lasing threshold as low as 0.8 kW cm À2 . [13] Recent activities [11] have demonstrated room-temperature lasing for optically pumped lasers in pulsed mode, while the state-of-the-art for electrically pumped lasers has achieved milestones up to 90 K. [19,20] Several efforts have been also devoted to study laser designs based on Fabry Perot cavities, [16] photonic crystals, [18,21] or microbridges.…”