Design and simulation of losses in Ge/SiGe terahertz quantum cascade laser waveguides

Abstract

The waveguide losses from a range of surface plasmon and double metal waveguides for Ge/Si 1−x Ge x THz quantum cascade laser gain media are investigated at 4.79 THz (62.6 µm wavelength). Double metal waveguides demonstrate lower losses than surface plasmonic guiding with minimum losses for a 10 µm thick active gain region with silver metal of 21 cm −1 at 300 K reducing to 14.5 cm −1 at 10 K. Losses for silicon foundry compatible metals including Al and Cu are also provided for comparison and to provide a guide for gain requirements to enable lasers to be fabricated in commercial silicon foundries. To allow these losses to be calculated for a range of designs, the complex refractive index of a range of nominally undoped Si 1−x Ge x with x = 0.7, 0.8 and 0.9 and doped Ge heterolayers were extracted from Fourier transform infrared spectroscopy measurements between 0.1 and 10 THz and from 300 K down to 10 K. The results demonstrate losses comparable to similar designs of GaAs/AlGaAs quantum cascade laser plasmon waveguides indicating that a gain threshold of 15.1 cm −1 and 23.8 cm −1 are required to produce a 4.79 THz Ge/SiGe THz laser at 10 K and 300 K, respectively, for 2 mm long double metal waveguide quantum cascade lasers with facet coatings.

THz intersubband electroluminescence from n-type Ge/SiGe quantum cascade structures

“…Finally it would be useful to clarify whether the ∆ 2 -states confined in the influence the electronics dynamics. To achieve laser action, we will leverage on the progress made in the material growth and structure modelling by employing higher gain structures based on 4-quantum wells 23 featuring a diagonal optical transition and embedded in double metal waveguides 43 . This project was funded by the European Union's Horizon 2020 research and innovation programme under Grant Agreement No.…”

Photonic Band Gap and Light Routing in Self-Assembled Lattices of Epitaxial Ge -on- Si Microstructures

“…Moreover, by virtue of the inherent transparency of group IV materials at long wavelengths, we expect that Ge/SiGe quantum well emitters embedded into microcrystals [28] can have strong potential for the implementation of VCSELs and quantum cascade lasers spanning the mid-infrared and terahertz range. [29,30]…”

Electron-phonon coupling in n -type Ge two-dimensional systems

“…However, in the last two decades, advances in group-IV epitaxy have made possible to grow SiGe multilayer systems with high crystal quality [4][5][6][7][8] ; consequently this class of materials is attracting increasing research efforts, mainly motivated by its prompt integrability with the mainstream CMOS standard. In particular, in the last ten years, SiGe Ge-rich structures have been actively investigated, and applications have been proposed in different contexts as for instance quantum computing [8][9][10] , Si-based photonics [11][12][13] , high mobility transistors 14,15 , and thermoelectricity 16,17 . The recently demonstrated 18 incorporation of Sn to obtain Ge-rich ternary SiGeSn alloys has further enlarged the design flexibility of this material system.…”