SPONTANEOUSLY FORMED LONG-RANGE AL-RICH AND GA-RICH ALXGA1-XAS ALYGA1-YAS SUPERLATTICE AND OPTICAL-PROPERTIES ENHANCEMENT IN (111)A ALGAAS/

Spontaneously formed long-range Al-rich and Ga-rich AlxGa1-xAs/AlyGa1- yAs superlattice in(111)A was demonstrated. This was observed by cross -sectional transmission electron microscopy (TEM) in 0.75 mu m Al0.30G a0.70As grown on (111)A GaAs substrates at 640 degrees C. In contrast, none of the above superstructure was observed by TEM on a side-by-sid e grown (100) oriented substrate. 15 K photoluminescence (PL) showed a 31 meV redshift and six times peak intensity enhancement in layers gr own on (111)A substrates to that on (100). A reduced long-range compos itional modulation can be achieved by growth at higher temperatures an d is shown in the finer and moderately modulating (111)A Al0.40Ga0.60A s grown at 700 degrees C. A 15 K PL linewidth of 17 meV was achieved i n 700 degrees C grown (111)A A(0.40)Ga(0.60)As that is the narrowest r eported linewidth for (111)A AlGaAs. (C) 1995 American Institute of Ph ysics.