Effect of Ionized Impurities at Heterointerface on Concentration and Mobility of Two-Dimensional Electrons in Selectively Doped Heterojunction Structures

The concentration N S and the low-temperature mobility µ of two-dimensional electron gas in GaAs/AlGaAs selectively doped heterojunctions have been studied theoretically and experimentally for the case where ionized impurities are present at heterointerfaces. It is found that N S scarcely changes when the concentration N IF of interfacial impurities is below 1×1011 cm-2, but it rapidly disappears at higher values of N IF if the impurities are of the acceptor type. In contrast, the mobility is found to decrease substantially even when N IF is as low as 109 cm-2. Based on these results, a quantitative guideline is drawn on the acceptable level of contamination in ultrahigh-vacuum wafer processings including molecular beam epitaxial regrowth.