Capture, storage, and emission of holes in Si/Si1−xGex/Si QWʹs for the determination of the valence band offset by DLTS

We report on the problem of 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. To observe a DLTS signal, the holes must be stored long enough (>1 ms) in the QW so that the thermal emission is the dominating process. We achieved sufficiently long storage times by using two different structures. The first one was obtained by selective growth which leads to a lateral limitation of the QW-layer, where the holes are localized. For the second ones, the localization of holes is due to the presence of Si1−xGex-islands.