EFFECT OF ION-BOMBARDMENT ON DEEP PHOTOLUMINESCENCE BANDS IN P-TYPE BORON-MODULATION-DOPED SI LAYERS GROWN BY MOLECULAR-BEAM EPITAXY

Broad photoluminescence (PL) bands (about 100 meV full width at half maximum) in the energy range between 0.70 and 1.03 eV are shown to be a frequently occurring feature in p-type boron-modulation-doped Si epilayers grown at low temperature by molecular-beam epitaxy. It is shown that the presence of a particular broad band (BE) is critically determined by the bias applied to the substrate during the growth. This gives evidence that these deep PL bands are at least partly induced by ion bombardment during the growth. To clarify their origin, the effect of the hydrogenation and the influence of a magnetic field on the PL bands are studied. The results obtained indicate the existence of at least four types of radiative centers. The observed correlation between x-ray-diffraction and PL measurements suggests that some of the BB's could be related to macrodefects, such as defect clusters. The optically detected cyclotron resonance (ODCR) technique is used to specify the spatial location of the BE-related defects in the structures. Information on the dependence of the electron mobility on the growth conditions is also obtained by ODCR. An active role of the boron dopants in the formation of the defects giving rise to the BB's is clearly demonstrated by comparing results from undoped Si epilayers grown under similar conditions.