OPTICAL AND STRUCTURAL-PROPERTIES OF SPONTANEOUSLY FORMED LONG-RANGE COMPOSITIONAL MODULATION IN (111)A AND (111)B ALGAAS

We have studied the spontaneously formed long-range Al-rich and Ga-ric h AlxGa1-xAs/AlyGa1-yAs superlattices in both (111)A and (111)B AlGaAs during epitaxial growth. The spontaneously formed compositional modul ation has been investigated by cross-sectional transmission electron m icroscopy in AlxGa1-xAs (x=0.3-0.4) grown on (111)A and (111)B GaAs su bstrates at 600-700 degrees C. In contrast, similar superstructures ar e not observed in layers simultaneously grown on (100) substrates. The observed structural compositional modulation is closely related to th e large peak energy redshift and peak intensity enhancement in 15 K ph otoluminescence (PL) of samples grown on both (111)A and (111)B orient ations to those on (100). The respective redshifts of PL peak energy f or (111)A and (111)B Al0.27Ga0.73As to that of (100) are 137 and 45 me V, while the PL integrated intensity enhancement to (100) amounts to 2 00 and 2000 times, respectively. The effect of compositional modulatio n is reduced with the increasing growth temperatures as shown in the c onsiderably less compositionally modulated (111)A and (111)B Al0.40Ga0 .60As grown at 700 degrees C. (C) 1996 American Institute of Physics.