Realization of high mobilities at ultralow electron density in GaAs-Al0.3Ga0.7As inverted heterojunctions

We report the first realization of extremely low free-carrier concentration (≤4×1010 cm−2) and high LN2 electron mobilities (∼1.8×105 cm2/V s) in the dark in inverted Al0.3Ga0.7As /GaAs(100) modulation-doped structures. The obtained results are all the more remarkable since the structures do not involve any superlattice or graded barrier, δ doping, or large spacer layer thicknesses. We attribute the observed properties to the high quality of the ambient in the molecular beam epitaxy system and the use of optimized growth kinetics and procedure as determined from reflection high-energy electron diffraction intensity behavior.