Structural and optical properties of Ge islands grown in an industrial chemical vapor deposition reactor

The use of Si based materials for optoelectronic applications is hampered b y the indirect nature of the band gap. One possible solution by which to im prove the radiative light emission is three-dimensional Stranski-Krastanow growth of Si1-xGex or pure Ge on top of Si. In this article we give a detai led overview about the growth kinetics observed for Ge growth in a standard production oriented chemical vapor deposition system. With increasing depo sition time, we observed the usual changeover from monomodal to bimodal isl and distribution. The island morphology and density can be controlled by va rying the growth conditions or by applying a thermal anneal after island gr owth. Island densities up to 2.3x10(10) cm(-2) have been obtained for depos itions at 650 degreesC. A Si cap layer is needed for photoluminescence meas urements as well as for some device structures. However, Si capping at 700 degreesC leads to nearly total dissolution of small islands and truncation of bigger dome-shaped islands. This can be prevented by reducing the deposi tion temperature and by changing the Si gas source. Photoluminescence measu rements demonstrate the high layer quality of Si capped islands by the clea r separation between the no-phonon line and the transversal optical (TO) re plica and the high peak intensities. The spectral range of the island lumin escence is between 1.35 (920 meV) and 1.50 mum (828 meV) and depends on the growth conditions. At 20 K, we found up to 70 times higher values for the integrated no-phonon and the TO luminescence from the islands, compared to the integrated intensity from the Si TO peak. Nevertheless, the high photol uminescence intensity can be further enhanced by a thermal treatment in a H -2 plasma. Clear island luminescence up to 200 K has been observed after su ch thermal treatment, which shows the potential of this material system for optoelectronic device applications. (C) 2001 American Institute of Physics .