Abstract:Unstrained Ge1−xSnx layers of various Sn concentration (1.5%, 3%, 6% Sn) and Ge0.97Sn0.03 layers with built-in compressive (ε = −0.5%) and tensile (ε = 0.3%) strain are grown by molecular beam epitaxy and studied by electromodulation spectroscopy (i.e., contactless electroreflectance and photoreflectance (PR)). In order to obtain unstrained GeSn layers and layers with different built-in in-plane strains, virtual InGaAs substrates of different compositions are grown prior to the deposition of GeSn layers. For u… Show more
“…Moreover such approach is more safe in this case taking into account the narrow bandgap of GeSn and quite large range of bowing parameters reported in the literature for this alloy. Additionally, it has been shown that the Bir-Pikus theory 49 can be applied to description of the strain-related shifts in the conduction and valence bands in this alloy 28 50 . This theory has been used by us to calculate the quantum confinement potential for electrons and holes in strained GeSn/Ge QWs.…”
It is shown that compressively strained Ge1−xSnx/Ge quantum wells (QWs) grown on a Ge substrate with 0.1 ≤ x ≤ 0.2 and width of 8 nm ≤ d ≤ 14 nm are a very promising gain medium for lasers integrated with an Si platform. Such QWs are type-I QWs with a direct bandgap and positive transverse electric mode of material gain, i.e. the modal gain. The electronic band structure near the center of Brillouin zone has been calculated for various Ge1−xSnx/Ge QWs with use of the 8-band kp Hamiltonian. To calculate the material gain for these QWs, occupation of the L valley in Ge barriers has been taken into account. It is clearly shown that this occupation has a lot of influence on the material gain in the QWs with low Sn concentrations (Sn < 15%) and is less important for QWs with larger Sn concentration (Sn > 15%). However, for QWs with Sn > 20% the critical thickness of a GeSn layer deposited on a Ge substrate starts to play an important role. Reduction in the QW width shifts up the ground electron subband in the QW and increases occupation of the L valley in the barriers instead of the Γ valley in the QW region.
“…Moreover such approach is more safe in this case taking into account the narrow bandgap of GeSn and quite large range of bowing parameters reported in the literature for this alloy. Additionally, it has been shown that the Bir-Pikus theory 49 can be applied to description of the strain-related shifts in the conduction and valence bands in this alloy 28 50 . This theory has been used by us to calculate the quantum confinement potential for electrons and holes in strained GeSn/Ge QWs.…”
It is shown that compressively strained Ge1−xSnx/Ge quantum wells (QWs) grown on a Ge substrate with 0.1 ≤ x ≤ 0.2 and width of 8 nm ≤ d ≤ 14 nm are a very promising gain medium for lasers integrated with an Si platform. Such QWs are type-I QWs with a direct bandgap and positive transverse electric mode of material gain, i.e. the modal gain. The electronic band structure near the center of Brillouin zone has been calculated for various Ge1−xSnx/Ge QWs with use of the 8-band kp Hamiltonian. To calculate the material gain for these QWs, occupation of the L valley in Ge barriers has been taken into account. It is clearly shown that this occupation has a lot of influence on the material gain in the QWs with low Sn concentrations (Sn < 15%) and is less important for QWs with larger Sn concentration (Sn > 15%). However, for QWs with Sn > 20% the critical thickness of a GeSn layer deposited on a Ge substrate starts to play an important role. Reduction in the QW width shifts up the ground electron subband in the QW and increases occupation of the L valley in the barriers instead of the Γ valley in the QW region.
“…In this case the strain-related shifts for CB, HH, LH, and SO band are calculated using the Bir-Pikus theory 72 , see proper formulas in the Methods section. So far it has been shown that this theory works very well in this material system in the range of low built-in strains 15,73 , i.e., the range which is considered in this work.Figure 3Conduction (Γ and L point) and the valence (HH, LH, and SO) band maxima for Ga 1−w Sn w QW material strained on virtual Ga 1-z Sn z substrate with z = 0.05, 0.10, and 0.15. Dashed lines show the conduction and valence band position for Si y Ge 1−x−y Sn x barrier lattice matched to the virtual substrate.…”
8-band
k
·
p
Hamiltonian together with envelope function approximation and planewave expansion method are applied to calculate the electronic band structure and material gain for Ge
1−w
Sn
w
/Si
y
Ge
1−x−y
Sn
x
/Ge
1−w
Sn
w
quantum wells (QWs) grown on virtual Ge
1-z
Sn
z
substrates integrated with Si platform. It is clearly shown how both the emission wavelength in this material system can be controlled by the content of virtual substrate and the polarization of emitted light can be controlled via the built-in strain. In order to systematically demonstrate these possibilities, the transverse electric (TE) and transverse magnetic (TM) modes of material gain, and hence the polarization degree, are calculated for Ge
1−w
Sn
w
/Si
y
Ge
1−x−y
Sn
x
/Ge
1−w
Sn
w
(QWs) with the strain varying from tensile (ε = +1.5%) to compressive (ε = −0.9%). It has been predicted that the polarization can be changed from 100% TE to 80% TM. In addition, it has been 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)), may ensure a respectable quantum confinement for electrons and holes in this system. With such material features Ge
1−w
Sn
w
/Si
y
Ge
1−x−y
Sn
x
/Ge
1−w
Sn
w
QW structure unified with Ge
1-z
Sn
z
/Si platform may be considered as a very prospective one for light polarization engineering.
“…The room-temperature electron mobility increases from 140 cm 2 /Vs in GeSnP1 to 175 cm 2 /Vs in GeSnP3. Since the Sn concentration is the same in all samples, the enhancement of the carrier mobility and the change of the band gap can be associated with the strain engineering and the band gap renormalization, respectively [46,47]. Figure 6b shows the values for the direct band gap in bulk Ge, tensile stained Ge-on-Si, undoped GeSn and very heavily doped GeSn alloys.…”
Ge with a quasi-direct band gap can be realized by strain engineering, alloying with Sn or ultra-high n-type doping. In this paper, we use all three approaches together -strain engineering, Sn alloying and n-type doping to fabricate direct band gap GeSn alloys. The heavily-doped n-type GeSn was realized using a CMOS-compatible non-equilibrium material processing. P is used to form a highly-doped n-type GeSn layers and to modify the lattice parameter of GeSn:P alloys. The strain engineering in heavily P-doped GeSn films is confirmed by X-ray diffraction and micro-Raman spectroscopy. The change of the band gap in GeSn:P alloy as a function of P concentration is theoretically predicted using density functional theory and experimentally verified by near-infrared spectroscopic ellipsometry.According to the shift of the absorption edge it is shown that for an electron concentration above 1×10 20 cm -3 the band gap renormalization is partially compensated by the Burstein-Moss effect. These results indicate that Ge-based materials have a large potential for the nearinfrared optoelectronic devices, fully compatible with CMOS technology.
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