GAAS(001) SURFACE BALANCED WITH ARSINE PARTIAL-PRESSURE IN METALORGANIC CHEMICAL-VAPOR-DEPOSITION REACTOR OBSERVED BY SURFACE PHOTOABSORPTION

We measured surface photoabsorption signals from As adsorbed surfaces of GaAs (001) substrates in a reactor of metalorganic chemical vapor d eposition (MOCVD) under various partial pressures of AsH3. Desorption of As atoms from the surface was balanced with adsorption of As atoms under AsH3 partial pressure. We found that the surface conditions vari ed as a function of the partial pressure and the temperature of the su bstrate. Comparing the experimental results with a multi-layer Langmui r adsorption model, we determined the phase boundaries of the surface structures under MOCVD conditions at temperatures between 500 and 700 degrees C. One of the boundaries was assigned to the boundary between (2x4) and c(4x4), and the other to that between c(4x4) and a surface o f excess As.