Optical absorption in highly strained Ge/SiGe quantum wells: the role of ⌈→Δ scattering

Lever, L., Ikonić, Z., Valavanis, A., Kelsall, R.W., Myronov, M., Leadley, D.R., Hu, Y., Owens, N., Gardes, F.Y. and Reed, G.T. (2012) Optical absorption in highly strained Ge/SiGe quantum wells: the role of ⌈→Δ scattering. Journal of Applied Physics, 112 (12), [123105]. (doi:10.1063/1.4768935).

Abstract

We report the observation of the quantum-confined Stark effect in Ge/SiGe multiple quantum well heterostructures grown on Si_0.22Ge_0.78 virtual substrates. The large compressive strain in the Ge quantum well layers caused by the lattice mismatch with the virtual substrate results in a blue shift of the direct absorption edge, as well as a reduction in the Gamma-valley scattering lifetime because of strain-induced splittings of the conduction band valleys. We investigate theoretically the Gamma-valley carrier lifetimes by evaluating the Gamma-to-Delta and Gamma-to-Delta scattering rates in strained Ge/SiGe semiconductor heterostructures. These scattering rates are used to determine the lifetime broadening of excitonic peaks and the indirect absorption in simulated absorption spectra, which are compared with measured absorption spectra for quantum well structures with systematically varied dimensions. We find that Gamma-to-Delta scattering is significant in compressively strained Ge quantum wells and that the Gamma-valley electron lifetime is less than 50 fs in the highly strained structures reported here, where Gamma-to-Delta scattering accounted for approximately half of the total scattering rate.

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Contributors

Author: F.Y. Gardes

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