Photoluminescence from ultrathin Ge-rich multiple quantum wells observed up to room temperature: Experiments and modeling

Abstract

Employing a low-temperature growth mode, we fabricated ultrathin Si1−xGex /Si multiple quantum well\ud structures with a well thickness of less than 1.5 nm and a Ge concentration above 60% directly on a Si substrate. We identified an unusual temperature-dependent blueshift of the photoluminescence (PL) and exceptionally low thermal quenching. We find that this behavior is related to the relative intensities of the no-phonon (NP) peak and a phonon-assisted replica that are the main contributors to the total PL signal. To investigate these aspects in more detail, we developed a strategy to calculate the PL spectrum employing a self-consistent multivalley effective mass model, in combination with second-order perturbation theory. Through our investigation, we find that while the phonon-assisted feature decreases with temperature, the NP feature shows a strong increase in the recombination rate. Besides leading to the observed robustness against thermal quenching, this causes the observed blueshift of the total PL signal

Photoluminescence study of interband transitions in few-layer, pseudomorphic, and strain-unbalanced Ge/GeSi multiple quantum wells

“…The electronic band structure and transition energies of the Ge MQWs samples and of the different buffer layers have been calculated relying on two different theoretical framework: a first-neighbor tight-binding Hamiltonian model 29,30 and a multivalley effective mass description 31 . The predictivity of these two models for the evaluation of electronic spectra in GeSi multilayer heterostructures is well established [32][33][34] , and indeed, compatible numerical results have been obtained when calculating the numeri- cal data discussed in this work.…”

Photoluminescence from GeSn nano-heterostructures

“…Interestingly, the PL peak position remains almost stable against the temperature increase, despite the expected bandgap shrinkage. Although a more systematic study with theoretical support is needed to clearly address this observation, we speculate that, as we observed also in Ge/Si ultra-thin multi quantum wells [20], a thermally activated transfer of oscillator strength from indirect (lower energy) to direct (higher energy) radiative transitions, which are almost degenerate at the Sn concentration here investigated (see schematics in the inset of figure 5(b)), could compensate for the T-driven shrinkage of the band gaps.…”

Composition analysis and transition energies of ultrathin Sn-rich GeSn quantum wells

“…The fabrication of low-dimensional structures such as Snrich quantum wells or quantum islands could be a route towards the realization of Ge 1−y Sn y structures with a Sn content high enough to obtain a direct band gap material while at the same time mitigating the influence of the lattice constant mismatch on layer quality [9,10]. Additionally, carrier confinement in these low-dimensional structures can be utilized to improve optoelectronic device properties [11].…”