EFFECT OF IONIZED IMPURITIES AT HETEROINTERFACE ON CONCENTRATION AND MOBILITY OF 2-DIMENSIONAL ELECTRONS IN SELECTIVELY DOPED HETEROJUNCTION STRUCTURES

The concentration N-S and the low-temperature mobility mu of two-dimensional electron gas in GaAs/A1GaAs 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 x 10(11) 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 10(9) 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.