GROWTH OF GASE ON AS-PASSIVATED SI(111) SUBSTRATES

We have studied the growth of GaSe on As-passivated Si(111) substrates by molecular beam epitaxy (MBE) for a wide range of substrate tempera tures (375-500 degrees C) and Se/Ga beam equivalent pressure (BEP) rat ios (similar to 30 to > 200). We see three distinct regions when our d ata are plotted as a phase diagram in Se/Ga BEP and growth temperature . For high Se/Ga BEP ratios and high substrate temperatures, continuou s layered structure GaSe films are formed on the substrate. Reflection high energy electron diffraction (RHEED) indicates that these films a re flat during growth, but after growth is stopped, the surface goes t hrough a transformation and becomes rough on a microscopic scale. At l ow Se/Ga BEP ratios and high substrate temperatures, small Ga droplets form on the substrate surface, and no GaSe forms on the substrate. Ga Se films with Ga droplets on the surface are formed when either the su bstrate temperatures or the Se/Ga BEP ratio is low. In this paper we w ill discuss possible mechanisms for growth (or the inhibition of growt h) in the three regions of our phase diagram and compare our results w ith those already published for MBE growth of GaSe on Si(111)7 x 7 and GaAs(111).