Measurement and modeling of ultrafast carrier dynamics and transport in germanium/silicon-germanium quantum wells

Edward L Ginzton Laboratory, Stanford University, 348 Via Pueblo Mall, Stanford, CA 94305, USA.
Optics Express (Impact Factor: 3.49). 12/2010; 18(25):25596-607. DOI: 10.1364/OE.18.025596
Source: PubMed


We measure the intervalley scattering time of electrons in the conduction band of Ge quantum wells from the direct Γ valley to the indirect L valley to be ~185 fs using a pump-probe setup at 1570 nm. We relate this to the width of the exciton peak seen in the absorption spectra of this material, and show that these quantum wells could be used as a fast saturable absorber with a saturation fluence between 0.11 and 0.27 pJ/μm. We also observe field screening by photogenerated carriers in the material on longer timescales. We model this field screening by incorporating carrier escape from the quantum wells, drift across the intrinsic region, and recovery of the applied voltage through diffusive conduction.


Available from: David A. B. Miller
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    • "The speed of MQW electroabsorption modulators is typically RC limited [39]. Ge/SiGe QW devices in particular should be relatively unaffected by saturation effects at higher optical intensities , due to the fast rate of carrier scattering out of the conduction band Γ valley [40]. A 3 dB bandwidth of 37 GHz has been previously reported in III–V AFPMs, and similar performance is likely attainable with optimization of the current Ge/SiGe devices. "
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    Journal of Lightwave Technology 12/2013; 31(24):3995-4003. DOI:10.1109/JLT.2013.2279174 · 2.97 Impact Factor
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    • "For the line shape, we have empirically chosen to use a hyperbolic secant (sech) function because of its relatively good agreement with experimental data. The FWHM includes homogeneous (e.g., from ultrafast carrier lifetimes [27]) and non-homogeneous broadening contributions (e.g., from well width fluctuations [19]). Characteristic exciton absorption peaks calculated this way are shown in Fig. 1 with the solid black line. "
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    ABSTRACT: With germanium showing significant promise in the design of electroabsorption modulators for full complementary metal oxide semiconductor integration, we present a simple electroabsorption calculator for Ge/SiGe quantum wells. To simulate the quantum-confined Stark effect electroabsorption profile, this simple quantum well electroabsorption calculator (SQWEAC) uses the tunneling resonance method, 2-D Sommerfeld enhancement, the variational method and an indirect absorption model. SQWEAC simulations are compared with experimental data to validate the model before presenting optoelectronic modulator designs for the important communication bands of 1310 nm and 1550 nm. These designs predict operation with very low energy per bit $({<}{rm 30}~{rm fJ}/{rm bit})$ .
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    ABSTRACT: Surface-illuminated vertical p-i-n Ge/SiGe multiple quantum wells photodiodes are demonstrated with a low dark current density of 200 mA/cm 2 and 10 GHz optical bandwidth at -1 V which reaches over The use of direct-gap transitions in group IV indirect-gap semiconductors such as Ge/SiGe heterostructures or bulk SiGe (1-8) provides a promising path towards the monolithic integration of light sources, optical modulators, and photodetectors. Particularly, Ge/Si0.15Ge0.85 multiple quantum wells (MQWs) have been demonstrated to exhibit strong light modulation based on the quantum confined Stark effect (QCSE) (6) within the spectral range from 1400 nm (0.89 eV) to 1440 nm (0.86 eV). Moreover, transient optical gain (7) and room temperature direct gap related photoluminescence (PL) (8) of Ge/Si0.15Ge0.85 multiple quantum wells have been reported with the PL spectra having peak intensity at about 0.88 eV. Therefore, the light detection performance of the Ge/SiGe MQWs within the same wavelength region is investigated in this paper. High speed operation of the Ge/SiGe MQWs is reported at 1405 nm (0.88 eV) using a simple surface illuminated vertical p-i-n photodiode with detection bandwidth as high as 30GHz. These results demonstrate the capability of Ge/SiGe heterostructures to work compatible with 40 Gbit/s data transmission.
    01/2011; DOI:10.1109/GROUP4.2011.6053807
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