Zhifeng Sui

Raman analysis of light‐emitting porous silicon

Porous silicon that strongly emits in the visible was analyzed using Raman scattering. The spectrum peaks near 508 cm−1, has a width of ∼40 cm−1, and is very asymmetric. Using a model of phonon confinement, this suggests that the local structure of porous silicon is more like a sphere than a rod and has a characteristic diameter of 2.5–3.0 nm. Polarization Raman measurements suggest that the structure does not consist of a series of parallel columns.

Raman analysis of Si/Ge strained-layer superlattices under hydrostatic pressure

Raman scattering was used to study optical phonons in a Si12Ge4 strained‐layer superlattice on c‐Si(001) that was subjected to hydrostatic pressure at room temperature. The change of phonon frequency with pressure, dω/dP, for the principal quasi‐confined LO mode in the Ge layers, is found to be significantly smaller than that for bulk crystalline Ge. This difference is shown to be due to the tuning of biaxial strain in the Ge layers and the pressure response of the confined mode as hydrostatic pressure is varied. Both strain and confinement make comparable contributions to dω/dP for the Ge layers in the superlattice examined here.

Photoluminescence of ZnSe/ZnMnSe superlattices under hydrostatic pressure

Photoluminescence near 4450 A (violet) and 5900 A (yellow) from ZnSe/Zn1−xMnxSe strained‐layer superlattices (SLS) is studied as a function of applied hydrostatic pressure up to ∼90 kbar for x=0.23, 0.33, and 0.51 at 9 K. For each of the three SLSs, the peak energy of the near‐band‐gap violet photoluminescence (PL) from exciton recombination increases sublinearly with pressure, and closely follows that of ZnSe. The observed dependence is consistent with type‐I band alignment, at least at pressures where the violet PL intensity remains strong. For the x=0.23 SLS, the energy of the biexciton PL increases faster than that of the exciton, which suggests decreased confinement. The yellow PL is due to the 4T1 →6A1 intraionic transition in Mn2+ and the nearly linear decrease of the peak energy of this signal with pressure is explained by crystal‐field theory. In most cases examined, the intensities of the violet and/or yellow PL decrease abruptly above a certain pressure that increases with x from ∼65 to ∼90 kba...