P2S5 PASSIVATION OF GAAS-SURFACES FOR SCANNING TUNNELING MICROSCOPY IN AIR

We report a novel method of GaAs substrate preparation which imparts significantly improved topographical and chemical uniformity to the surface. The procedure, employing an aqueous P2S5/(NH4)2S solution, leaves the surface in a highly ordered state and resistant to air oxidation for periods of a day or more without the presence of foreign chemical layer such as sulfur. Surface quality was determined by scanning tunneling microscopy (STM), time-of-flight secondary ion mass spectrometry, reflection high-energy electron diffraction, and x-ray photoelectron spectroscopy. The remarkable stability and smoothness of treated III-V surfaces is illustrated by STM imaging of an Al0.51GaO.49As/GaAs superlattice in air. The superlattice consisted of periodic alternating AlGaAs/GaAs layers of various thicknesses from 10 to 1000 nm.