  Heavily-alloyed, 100 nm Ga1-xMnxAs (x>0.1) films are obtained via low
temperature molecular beam epitaxy utilizing a combinatorial technique which
allows systematic control of excess arsenic during growth. Reproducible,
optimized electronic, magnetic and structural properties are found in a narrow
range of stoichiometric growth conditions. The Curie temperature of
stoichiometric material is 150-165 K and independent of x within a large window
of growth conditions while substitutional Mn content increases linearly,
contradicting the prediction of the Zener Model of hole-mediated
ferromagnetism.
