Investigation of short period AlAs/GaAs superlattices as conduction-band barriers

Abstract

Short period AlAs/GaAs superlattices, or pseudoalloys, are investigated as insulators in n+ GaAs–insulator–n GaAs structures, or superlattice barrier capacitors (SLBC’s), and as tunneling barriers in superlattice double barrier diodes (SLDBD’s). The energies of the lowest superlattice states in the SLBC’s and the energies of the quantum well quasibound states in the SLDBD’s are determined using thermionic emission analysis. Depending on the GaAs and AlAs layer thicknesses, the lowest states in the SLBC’s may be Γ states in the GaAs layers or X states in the AlAs layers. It is also possible for the barrier to behave as a random alloy. We observe all three cases. The SLDBD’s exhibit strong negative resistance at low temperatures and we find evidence that the superlattice barriers (SLB’s) behave as ideal Γ band structures, regardless of the layer thicknesses. Second current peaks which are attributed to resonant states in the SLB’s appear in the SLDBD I–V curves when the GaAs layers are thicker than 5 monolayers.