Effect of oxygen incorporation at AlGaAs/GaAs interfaces on the electrical properties of two-dimensional electron gas

We have investigated the carrier concentration and mobility of the two-dimensional electron gas (2DEG) in AlGaAs/GaAs selectively doped heterojunction structures that involve oxygen impurities at the heterointerfaces. The oxygen impurities were incorporated during growth interruption of molecular beam epitaxy at the interfaces for several tens of minutes. It is shown that the carrier concentration of the 2DEG does not change for the areal density of the oxygen impurity up to 6×1011 cm−2, but it decreases drastically when the oxygen density exceeds 3×1012 cm−2. In contrast, the decrease of the mobility is observable for a much smaller oxygen density of the order of 1010 cm−2. We show that these influences are well explained by the formation of charged states at the interface.