ULTRA-HIGH-VACUUM SCANNING TUNNELING MICROSCOPE OBSERVATION OF VICINAL (001) GAAS SURFACE AND (117)B GAAS SURFACE GROWN BY METALORGANIC VAPOR-PHASE EPITAXY

We have observed the atomic arrangement on vicinal (001) GaAs surfaces and (117)B GaAs surface grown by metalorganic vapor phase epitaxy usi ng an ultra high vacuum scanning tunneling microscope without exposure to air. Multilayer step regions and atomically flat terrace regions a n alternately observed to the misorientation direction for both (001) GaAs surfaces misoriented by 2 degrees toward [110] direction (called A-surface) and [(1) over bar 10] direction (called B-surface). At the terrace region, c(4 x 4) reconstruction units are dominant. For B-surf ace, (4 x 2) and (4 x 3) like reconstruction units were observed betwe en each monolayer step at multilayer step region, which correspond to (119)B GaAs surface. For A-surface, the reconstruction units are not c lear at multilayer step region, but step-step separation is about 1.4 nm, which is close to (117)A GaAs surface. For(117)B GaAs surface, a l ot of monolayer steps and (4 x 3) and (5 x 3) like reconstruction unit s were observed with significant undulations for whole area, which sug gests that (117)B GaAs surface grown by MOVPE is thermodynamically uns table.