Modeling of the electronic band structure and the material gain in GeSn-based quantum wells

In our recent work we have shown that the compressively stained GeSn/Ge quantum well (QW) is a very promising gain medium for lasers integrated with Si platform [1]. The material gain for such QW can be tuned in broad spectral range which is interesting for gas sensing. Since Ge
_1-w
Sn
_w
QW can be integrated with Si platform via Ge
_1-z
Sn
_z
virtual substrate it is also possible to grown tensile strained Ge
_1-w
Sn
_w
QWs when w <; z. In this case the built-in strain enhances the direct character of bandgap and because of this is very favorable for laser applications. On the other hand the material gain spectrum for tensile strained QWs can be dominated by the transverse magnetic (TM) mode since the ground state transition in such QWs is between the electron and the light-hole subband instead of the heavy-hole subband. In this work it is shown that emission wavelength in this material system can be controlled by the content of virtual substrate while the polarization of emitted light can be controlled via the built-in strain. To demonstrate this phenomenon the transverse electric (TE) and transverse magnetic (TM) mode of material gain, and hence the polarization degree, are calculated for Ge
_1-w
Sn
_w
/Si
_y
Ge
_1-x-y
Sn
_x
(QWs) with the strain changing from tensile (ε = +1.5%) to compressive (ε = -1.4%). It has been observed that the polarization degree can be tuned from 100% TE to 80% TM. In addition it is shown that Si
_y
Ge
_1-x-y
Sn
_x
barriers lattice matched to the virtual Ge
_1-z
Sn
_z
substrate (condition: y = 3.66(x-z)) ensure a good quantum confinement for electrons and holes in this material system. With such material features Ge
_1-w
Sn
_w
/Si
_y
Ge
_1-x-y
Sn
_x
QW system integrated with Ge
_1-z
Sn
_z
/Si platform is very perspective for light polarization engineering [2].