Stability of a low-temperature grown GaAs surface layer following air exposure using tunneling microscopy

The stability of a GaAs layer structure consisting of a thin (10 nm) layer of low‐temperature‐grown GaAs on a heavily n‐doped GaAs layer, both grown by molecular beam epitaxy, has been studied using a scanning tunneling microscope. The sample was exposed to the atmosphere between the layer growth and STM characterization. Tunneling spectroscopy shows both the GaAs band edges and a band of midgap states associated with the excess As in the surface layer. The observation of midgap states following atmospheric exposure indicates that the low‐temperature‐grown GaAs layer does not oxidize rapidly. The spectroscopy results are used to confirm a model for conduction in low resistance, nonalloyed contacts employing comparable layer structures.