ABSTRACT
Some rare earth elements, such as Er, are donors for InSb. Carrier density and mobility data on bulk Er-doped InSb films, grown by molecular beam epitaxy on semi-insulating InP, were reported in the past. Here, we study a sequence of similar films, δ-doped with Er, and vary the spacing between the layers (or the number of layers NL in a 1.6 μm thick region of the films), and the areal Er atom density in each layer, NEr, so that the volume density of Er averaged over the whole film, n Er. includes the doping range of previous work. In bulk-doped films, the low-temperature electron density n is a linearly increasing function of Er concentration n Er up to n ≈ 1xl017 cm-3, above which it saturates, but this is not the case in the δ-doped samples. For NL = 48, n increases with NEr up to n ≈ 1x1017 cm-3, just like in bulk-doped films, but instead of saturating, n decreases when NEr is further increased. The mobility of the δ-doped samples with NEr ≤ 2.5x1013 cm-2 is enhanced over that of bulk-droped films with similar Er and electron concentrations. This effect is more pronounced at lower temperature and at lower Er concentrations.
