Temperature and excitation power dependencies of the photoluminescence of planar and vertically self-organized Si0.70Ge0.30/Si strained superlattices

We have studied the correlation between the morphological characteristics and the photoluminescence (PL) behavior of nominally 20-nm Si/7-nm Si0.70Ge0.30 superlattices (SLs) showing planar SiGe layers (#1) and vertical self-aligned undulations (#2). At 8 K and low PL excitation density, no-phonon (NP) peaks were centered at 919 and 934 meV, for SLs #1 and #2, respectively. increasing excitation power resulted in a high-energy side broadening and a strong blue-shift of sample #2 peaks, which were interpreted by in-plane localization and spreading of the hole wave function within the thickness undulations. Up to intermediate temperature values (similar to 120 K), carrier diffusion and localization at the crest (similar to 11 nm) of the undulations enhanced PL efficiency. Room temperature SiGe PL was observed for both samples with an intensity exponential decay above 150 K. Activation energies of 260 meV (#1) and 172 meV (#2) were derived from Arrhenius plots. The energy difference can be explained by the lateral channel formed by the troughs (similar to 2 nm) in the long scale (similar to 120 nm) waviness of sample #2 that assists hole thermoionic emission in the Si barriers. (C) 2000 Elsevier Science B.V. All rights reserved.