Examination of MBE GaAs/Al0.3Ga0.7As superlattices by Auger electron spectroscopy

Abstract

MBE GaAs/Al0.3Ga0.7As superlattices have been examined by Auger electron spectroscopy (AES) using Ar+ sputter depth profiling and line scans across the crater wall left after depth profiling. The superlattice was grown by MBE with ten periods of alternating Al0.3Ga0.7As and GaAs layers of 200 and 50 Å thickness, respectively, at a substrate temperature of 700 °C. AES sputter depth profiling clearly indicated the periodic nature of the structure through all ten periods, although the Al signal did not appear to drop to zero in the GaAs layers, probably due to sputter effects. The use of the standard elemental Auger sensitivity factor for Al (0.070 at 5 kV) yielded the correct atomic concentration of Al in the Al0.3Ga0.7As layers (15% for x=0.3), however, this was not true for either Ga or As. By using an AES line scan up the sputter crater wall, the superlattice layers were spread out by a factor of ∼2400. The periodicity of the structure was more strongly evident than that seen by AES depth profiling with the Al signal dropping to zero in the scanned crater wall regions corresponding to the 50 Å GaAs layers. The expanded superlattice was also examined by absorbed current and secondary electron imaging and by AES mapping.