EFFECTS OF GAAS-SUBSTRATE SURFACE MISORIENTATION FROM (001) ON BAND-GAP ENERGY IN GA0.5IN0.5P

The dependence of band-gap energy (E(g)) on GaAs-substrate surface ori entation was systematically studied for metalorganic vapor phase epita xial growth Ga0.5In0.5P on GaAs at a growth temperature of 660-degrees -C and a V/III ratio of 140 approximately 150. When the misorientation angle theta(B) increased from the exact (001) to (111)B, E(g) decreas ed from 1.85 eV and took a minimum value of 1.83 eV at theta(B) = 4-de grees approximately 6-degrees. When theta(B) increased from 4-degrees approximately 6-degrees to 15.8-degrees (i.e., (115)B), E(g) increased steeply to a nearly-normal value of 1.90 eV. Then, E(g) gradually rea ched a normal value of 1.918 eV, as theta(B) reached 54.7-degrees (i.e ., (111)B). The (115)B surface was found to be a critical misorientati on. On the other hand, when increasing the misorientation angle theta( A) from the exact (001) to (111)A by 4-degrees approximately 6-degrees , E(g) increased sharply towards the normal value. For further increas e of theta(A), E(g) still increased monotonically towards a value of 1 .916 eV at (111)A, which is virtually the same as that for the (111)B surface. These E(g) behaviors were found to correspond to the degree o f ordering characterized by the transmission electron microscopic stud y of (111)B CuPt-type ordering on the Group III sublattice. A possible explanation is given for the E(g) behaviors on the basis of step-terr ace reconstructions on the grown surfaces.