Material Properties of Si-Ge/Ge Quantum Wells

Abstract

Photocurrent measurements in Ge quantum wells and quantum tunneling resonance simulations give the first measurements of effective masses and other parameters for design of high-performance SiGe/Ge quantum well optoelectronics on silicon.Germanium is increasingly important for integrating photonics into silicon IC technology. Recent demonstrations of quantum wells (QWs) [1] open many new device possibilities, including highperformance optical modulators based on the quantum-confined Stark effect (QCSE) [2]. Relatively little is, however, known about the key properties needed for QW device design. Here we investigate the shifts of multiple different transitions for the first time in such QWs, fitting experimental photocurrent results with quantum-mechanical tunneling resonance calculations. We give the first experimental characterization of the effective masses and direct bandgaps of Ge and Ge-rich SiGe structures including the effects of strain. Though both Si and Ge are indirect gap materials, the QWs produce the QCSE at the Ge direct bandgap [1]. The measured and simulated QCSE shifts of various different transitions are shown in Fig. 1. By using a relatively large Ge QW width of 22nm, numerous transitions can be seen, corresponding to three confined electron levels and three heavy hole levels. These energy levels and the valence and zonecenter "direct" conduction band energy positions are shown in Fig. 2.

Indirect absorption in germanium quantum wells

“…To calculate the two transitions from conduction to LH and HH, the splitting energies of the LH and HH as deduced by QCSE spectra (simulated in SQWEAC) are added to the relevant band gap. 22,33 The indirect masses associated with the conduction bands are calculated according to the model presented by Rieger, 34 while the LH and HH masses are calculated in the same way as presented in the SQWEAC model. 22,33 …”

Ge/SiGe quantum confined Stark effect electro-absorption modulation with low voltage swing at λ = 1550 nm

“…Assuming that each electron in the photocurrent is due to one photon being absorbed, 4.4 % of the photons leaving the fibre lens are absorbed equating to an minimum absorption coefficient of 1875 cm −1 at 1471 nm. This is an improvement over previously reported absorption figures of 1600 cm −1 at 1450 nm using a similar number of ten QWs of 17 nm thickness with 40 nm thick barriers [24] but lower than the lower wavelength results at 1410 nm with an absorption of ∼3000 cm −1 using fifty Ge QWs of 10 nm thickness with 15 nm thick barriers [25]. The simulated spectrum in Fig.…”

Qubits in Double Quantum Well Structure

“…As the the DQW structure we choose the material which can be produced on the basis of Si 1−x Ge x /Geheterostructure [5], where two Si-wells are separated by the Si 0.16 Ge 0.84 -barrier of about 0.35 eV height. The purify of Si and Ge in such structure up to 10 11 cm −3 or even 10 10 cm −3 is possible [6].…”