THE INTERACTION OF HYDROGEN WITH GaAs SURFACES

Aspects of the interaction of hydrogen with MBE grown GaAs surfaces have been studied in situ with synchrotron radiation excited photoemission core level spectroscopy.We show how this characterization technique is a sensitive probe of the surface chemical composition.Using this technique, the GaAs(100) and (111) surface phase diagram at room temperature has been obtained as well as aspects of the AlAs surface.The measurements showed that for GaAs(100) the surface reconsuuctions proceed through a series of centered [c(4x4), ~(2x8) c(8x2)I and primitive structures [(1x6) ,(4x6)] and for the (111) surface (2x2).(J3x J 3)R(30°), ( J 19xJ 19)R(23.4O)as the surface As to Ga ratio is decreased.The study of the clean surfaces has been extended with an investigation of the interaction with atomic and molecular hydrogen.This is of interest both because hydrogen is a common growth ambient and because there is some indication that MBE growth in the presence of hydrogen improves crystal electrical quality.In all cases, the experiments showed a saturation hydrogen coverage was achieved at an exposure of 1 0 6 ~ of hydrogen when a cracking filament is used.Core level spectroscopy shows that the surface composition is modified by the presence of hydrogen and we have deduced a mechanism whereby the hydrogen forms a surface gallium hydride which sublimes.The hydrogen converts the clean surface reconstructions to a distinct semiconducting reconstruction with a specific composition independent of the starting reconstruction.These results indicate that hydrogen could modify the MBE growth surface thereby effect impurity incorporation.