Group IV Light Sources to Enable the Convergence of Photonics and Electronics

Abstract

Group IV lasers are expected to revolutionize chip-to-chip optical communications in terms of cost, scalability, yield, and compatibility to the existing infrastructure of silicon industries for mass production. Here, we review the current state-of-the-art developments of silicon and germanium light sources toward monolithic integration. Quantum confinement of electrons and holes in nanostructures has been the primary route for light emission from silicon, and we can use advanced silicon technologies using top-down patterning processes to fabricate these nanostructures, including fin-type vertical multiple-quantum-wells. Moreover, the electromagnetic environment can also be manipulated in a photonic crystal nanocavity to enhance the efficiency of light extraction and emission by the Purcell effect. Germanium is also widely investigated as an active material in Group IV photonics, and novel epitaxial growth technologies are being developed to make a high quality germanium layer on a silicon substrate. To develop a practical germanium laser, various technologies are employed for tensile-stress engineering and high electron doping to compensate the indirect valleys in the conduction band. These challenges are aiming to contribute toward the convergence of electronics and photonics on a silicon chip.

Group IV Direct Band Gap Photonics: Methods, Challenges, and Opportunities

“…Very thin membranes (Sánchez-Pérez et al, 2011), nanowires clamped in bulky mechanical strain apparatus (Greil et al, 2012), Ge bulk layers on III-V substrates (Huo et al, 2011), etc., are not considered here because they are unpractical for integration on Si. Not considered either is light emission from Si-based quantum wells and defects; for a recent review, see Saito et al (2014). In our compilation, Figure 2, we benchmark the two strain loadings (uniaxial and biaxial) and Sn alloy composition against the achieved relative band offset, ΔE/E0, where an offset ΔE of 100% is equal to E0 ~ 140 meV for the case of unstrained Ge.…”

Enhanced light emission from improved homogeneity in biaxially suspended Germanium membranes from curvature optimization

“…Germanium (Ge) is a promising contender in developing such a light source due to its epitaxial compatibility with Silicon, despite being an indirect bandgap material [6], which results in poor innate light emission due to phonon assisted photo radiative recombination. Ge can be converted into a direct bandgap material via the application of n-type doping and tensile strain [7][8][9]. An optically pumped Ge laser diode was reported at room temperature with 0.24% biaxial strain and 1 x 10 −19 cm −3 n-type doping [10] as well as an electrically pumped laser with 4 x 10 19 cm −3 n-type doping [11].…”

Spin-on doping of germanium-on-insulator wafers for monolithic light sources on silicon

“…13) Therefore, it is necessary to develop a process for high donor doping in Ge while minimizing the damage in the crystal lattice, 10) and enable the fabrication of a high efficiency Ge LD. 19) In fact, lasing from Ge by optical pumping, 20) and electrical pumping, 21) were reported. However, so far, other research groups have not yet reproduced their results 22) in spite of the significant efforts in the last few years.…”

“…7,25) However, there is a trade-off relationship between high crystalline quality and the doping concentration. 7,25) As a result, it is difficult to achieve doping concentration above 2×10 19 cm -3 without degradation of the crystal. 7,25) In order to overcome this problem, several approaches are proposed such as gas 3 immersion laser doping (GILD) where a doping concentration of 5.6×10 19 cm -3 was achieved.…”