Direct mapping of electronic structure across Al0.3Ga0.7As/GaAs heterojunctions: Band offsets, asymmetrical transition widths, and multiple-valley band structures.

By using the prototypical ${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As/GaAs system, we demonstrate the unique capability of scanning tunneling microscopy to directly map out detailed electronic structure across heterojunctions. Three novel applications are reported: (1) precise determination of band offsets, (2) measurement of asymmetrical electronic transition widths between the normal and inverted interfaces, and (3) mapping of multiple-valley band structures. Important implications of these results are discussed.