High-Pressure Photoluminescence Studies of Pseudomorphic Si1-yCy/Si MQW Structures

Abstract

We have performed photoluminescence (PL) investigations of pseudomorphic Si1–yCy/Si (y = 0.45, 1.05, and 1.62%) multiple quantum well (MQW) structures under hydrostatic pressure (0 to 8 GPa) and at low temperatures (10 to 70 K). The main MQW‐related emission, at energies below the Si band gap, consists of bound and free exciton no‐phonon lines and related Si transverse‐optic phonon replicas. All MQW‐related PL peaks shift to lower energy with increasing pressure at a rate characteristic for Γ–X indirect transitions in tetrahedral semiconductors. The total band offset and the activation energies for decay of the free and bound exciton emission increase slightly with pressure as a result of the larger negative band gap pressure coefficient of the strained pseudomorphic Si1–yCy layers compared to pure silicon. A separation of biaxial strain effects on the conduction and valence band near‐gap states in the pseudomorphic Si1–yCy layers (y ≤ 0.02) on Si indicates a decrease of the intrinsic Si1–yCy band gap which corresponds to that of pure silicon compressed to the lattice constant of the alloy. From this a type‐I band alignment with electrons and light holes localized in the SiC layers is inferred. This assignment is consistent with the dependence of PL‐peak intensities and energies on excitation power, temperature and pressure.

On the observation of electron-hole liquid luminescence under low excitation in Al2O3-passivated c-Si wafers

“…Figure 1 shows representative PL spectra recorded at temperatures from 40 K to 4 K for both the 0.4 and the 2.5 Ω cm c-Si wafers passivated by a 25 nm-thick layer of Al 2 O 3 annealed at 375 °C. At 40 K the PL spectra are characterized by an emission line at 1.098 eV and a low energy shoulder, which are related to the indirect, transverse-optical (TO) phononassisted transition of free (FE) and bound excitons (BE), respectively [13]. The excitonic emission dominates the PL spectra down to about 25 K, where the appearance of an additional PL band at (∼1.088 eV) sets in.…”