Structural properties of MnAs thin films grown by molecular beam epitaxy on (001) GaAs

Two different types of MnAs films have been grown by molecular beam epitaxy on GaAs (001) substrate. Both types of the films are composed of mainly a hexagonal MnAs phase and partially an orthorhombic MnAs phase at room tempe rature, but their orientations relative to the substrates differ with the t ype of film. High-resolution electron microscopy images indicate that the f ilms have abrupt interfaces with the substrates. The results of X-ray diffr action study at room temperature indicate that one type of film called type -a has more of the orthorhombic phase than the other type, type-B, does. Th e residual stresses existing in the phases are determined indirectly and ap proximately correspond, respectively, to hydrostatic pressures of 1.0 kbar and 2.5 kbar fur the hexagonal and orthorhombic phases in type-a films and 1.8 kbar and 2.0 kbar fur the hexagonal and orthorhombic phases in type-B f ilms. Here, negative pressure means tensile stress. The pressure-temperatur e phase diagram of bulk MnAs shows that in the corresponding ranges of hydr ostatic pressures at room temperature, hexagonal and orthorhombic phases ca n be stabilized.