Modulation-doped (Al,Ga)As/AlAs superlattice: Electron transfer into AlAs

Abstract
A modulation‐doped superlattice of n‐(Al,Ga)As and undoped AlAs has been grown by molecular beam epitaxy. At cryogenic temperatures, electrons transfer into the undoped AlAs layers and enhanced mobilities as high as 1000 cm2/Vs are observed for the first time. It is shown that by properly accounting for the depth of the donor level in modulation‐doped heterostructures reasonably good limits can be set on the gamma point conduction‐band discontinuity at the heterojunction. It is found that this discontinuity is approximately 60–65% of the band‐gap difference between the two alloys, in good agreement with other recent determinations.