In this article we study the electroluminescence of p-i-n diode structures with Ge dots consisting of coherent three-dimensional small ͑pyramids͒ and larger ͑dome͒ islands. The Ge dots are formed through strain-induced islanding. The diode structures, including one layer with Ge dots, were deposited on Si mesas with variable areas in order to study the influence of limited area deposition on self-assembling. It was observed that the reduction of deposited area improves island uniformity. The combined analysis of island distribution and electroluminescence spectra has lead to the conclusion that domes in small diodes have a smaller Si content or are less relaxed than domes in larger diodes. The diodes are found to emit up to room temperature near the optical communication wavelength of 1.3 microns.

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We report on the determination of the valence band offset between strained Si1−xGex and unstrained Si layers by deep level transient spectroscopy (DLTS) on Si/Si1−xGex/Si quantum well (QW) structures. A problem of this technique is to store the holes long enough (≥1 ms) in the QW so that the thermal emission of holes is the dominating process. We achieved sufficiently long hole storage times by using two different structures. In the first ones, this is obtained by selective growth which leads to a lateral limitation of the smooth QW layer, and with good Schottky contacts. For the second ones, the localization of holes is due to the presence of Si1−xGex islands. For a sample containing a smooth QW with XGe=0.17 a valence band offset of 140±20 meV was obtained and for the island layer with XGe=0.3 a value of 258±20 meV was found. These results are in good agreement with theory. The DLTS measurements are compared to admittance spectroscopy results and photoluminescence measurements.

The influence of molecular hydrogen (H 2 ) on the structural and optical properties of self-assembled Ge dots grown on Si͑001͒ has been studied using atomic force microscopy and photoluminescence spectroscopy ͑PL͒. Without hydrogen, a well known bimodal island size distribution occurs with small ͕105͖ faceted pyramids, and larger multifaceted domes. In the presence of an additional H 2 flow, we observe that a higher density of smaller pyramids and a lower density of domes occurs. Moreover, in the presence of hydrogen, PL investigations have revealed a thicker wetting layer thickness, probably due to a reduction of the surface diffusion length.

Plastic relaxation of Si 1−x Ge x layers on (100) Si leads to formation of misfit dislocations at the heterointerface and threading dislocations through the heterostructure. We report here a deep-level transient spectroscopy (DLTS) investigation of dislocations in n-type Si/Si 0.88 Ge 0.12 /Si heterostructures grown by selective epitaxy using low-pressure chemical vapour deposition (LPCVD). DLTS was used to detect deep states correlated with dislocations. Measurements were performed on large-area samples (relaxation degree of 63%) as well as on small areas (relaxation degree of 4%) grown selectively on the same wafer. The bias-dependent DLTS peak heights are consistent with a spatially varying dislocation density. This variation, and the combined interpretation of the corresponding DLTS peaks from large and small areas, allowed us to associate one of the deep levels with misfit dislocations at the heterointerface, a second one with threading dislocations and the third one with defects present in the SiGe layer near the interface.