HIGH-QUALITY INXGA1-XAS/INALAS MODULATION-DOPED HETEROSTRUCTURES GROWN LATTICE-MISMATCHED ON GAAS SUBSTRATES

We report on the lattice-mismatched growth and properties of InGaAs/InAlAs modulation-doped heterostructures on GaAs substrates for a full In composition range, by molecular beam epitaxy using a linearly graded InGaAs or InGaAlAs buffer layer grown at a relatively low temperature. High electron mobilities of 25,000 to 118,000 cm2/V.s were obtained at 77 K for In composition from 0.3 to 0.8. The observed monotonical increase of mobility in this In composition range agreed well with the theoretical calculation. It has been shown that the use of wider bandgap material, such as InGaAlAs, in the graded buffer layer is very effective in reducing the residual carrier concentration from 1 x 10(12) to less than 1 x 10(11) cm-2.