Modeling of a SiGeSn quantum well laser

Abstract

We present comprehensive modeling of a SiGeSn multi-quantum well laser that has been previously experimentally shown to feature an order of magnitude reduction in the optical pump threshold compared to bulk lasers. We combine experimental material data obtained over the last few years with k • p theory to adapt transport, optical gain, and optical loss models to this material system (drift-diffusion, thermionic emission, gain calculations, free carrier absorption, and intervalence band absorption). Good consistency is obtained with experimental data, and the main mechanisms limiting the laser performance are discussed. In particular, modeling results indicate a low non-radiative lifetime, in the 100 ps range for the investigated material stack, and lower than expected Γ-L energy separation and/or carrier confinement to play a dominant role in the device properties. Moreover, they further indicate that this laser emits in transverse magnetic polarization at higher temperatures due to lower intervalence band absorption losses. To the best of our knowledge, this is the first comprehensive modeling of experimentally realized SiGeSn lasers, taking the wealth of experimental material data accumulated over the past years into account. The methods described in this paper pave the way to predictive modeling of new (Si)GeSn laser device concepts.

Design of a waveguide-coupled GeSn disk laser

“…From modeling [9] of the optically pumped multiquantum-well GeSn/SiGeSn microdisk laser with experimental results published in [5], we estimate the electron concentration at threshold to be 3.5e17 cm -3 inside the wells at 20 K and the modal gain to be 600 cm -1 , pointing to high internal losses due to surface roughness as well as inter-valence-band and inter-conduction-valley free carrier absorption. Optical losses in an electrically pumped structure will be even higher due to the doping required for carrier transport.…”

Modeling and design of an electrically pumped SiGeSn microring laser

“…Using only a top stressor, on the other hand, results in the structure bending further down, improving the isotropy of the tensile strain in the xy-plane. However, the magnitude of the strain will then vary much more along the growth direction, as a consequence of this deformation [6,12]. For instance, if the 2.7 GPa stressor layer mentioned above is deposited only on top of the layer stack, for example immediately after growth and before any further device processing, the strain (ε || ) will vary from -0.076% compressive at the bottom of the GeSn active region to 0.53% tensile at the top of the stack.…”

“…The SiGeSn LD, the main focus of this work, has been studied intensively in the last decade. A lot of progress has been made, even though the limited directness of the GeSn gain material, i.e., the L-to Г-energy separation (∆E "Г ), as well as the high dark recombination rates arising from a high density of point defects are still limiting the maximum lasing temperature and efficiency [12]. Experimentally, the LDs have been improved regarding their operating temperature [13,14] and lasing threshold [15].…”

“…The net gain is modeled in the following as a function of injected current in order to determine the temperature dependent lasing thresholds. Models and basic assumptions regarding material properties are the same as in [12]. First experimental results are shown for both a non-underetched and an underetched microring LD and compared with each other.…”

Flip-chip-integrated silicon nitride ECL at 640nm with relaxed alignment tolerances

“…As a CMOS processing compatible alternative, group IV gain materials based on the silicon-germanium-tin (SiGeSn) system are also being very actively investigated, 2 however important challenges remain related to achievable alloy compositions and material quality. 3 Heterogeneous integration of compound semiconductors via wafer bonding, 4 on the other hand, has already reached commercial maturity.…”