Abstract
Theoretical calculation using the model solid theory is performed to design the stack of a group-IV laser based on a fully strained Ge1−xSnx active layer grown on a strain relaxed Si1−y−zGeySnz buffer/barrier layer. The degree of strain relaxation is taken into account for the calculation for the first time. The transition between the indirect and the direct band material for the active Ge1−xSnx layer is calculated as function of Sn content and strain. The required Sn content in the buffer layer needed to apply the required strain in the active layer in order to obtain a direct bandgap material is calculated. Besides, the band offset between the (partly) strain relaxed Si1−y−zGeySnz buffer layer and the Ge1−xSnx pseudomorphically grown on it is calculated. We conclude that an 80% relaxed buffer layer needs to contain 13.8% Si and 14% Sn in order to provide sufficiently high band offsets with respect to the active Ge1−xSnx layer which contains at least 6% Sn in order to obtain a direct bandgap.
Highlights
The colored region corresponds to the case in which the point is lower than L point in the conduction band resulting in a direct bandgap material
Theoretical calculations using the model solid theory were performed to design a group-IV laser stack based on a fully strained Ge1−xSnx active layer grown on strain relaxed Si1−y−zGeySnz buffer/barrier layer
If the strain relaxed buffer (SRB) has a sufficiently large lattice constant, the epitaxial Ge1−xSnx layer grown on top of it will always be a direct bandgap material
Summary
This strain relaxed buffer (SRB) layer does require a controlled lattice constant and a large bandgap to enable effective carrier confinement in the active Ge1−xSnx layer in both the conduction and valence bands. Si1−y−zGeySnz is a potentially suitable material for the buffer and barrier layers because the lattice constant and the energy bandgap can be simultaneously controlled by choosing appropriate Sn and Si contents.[8,9] we propose to use an epitaxial stack layer consisting of a direct bandgap Ge1−xSnx active layer coherently grown on a Si1−y−zGeySnz SRB for a group IV laser with a high optical gain.
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