Phase separation in oxygen deficient gallium oxide films grown by pulsed-laser deposition

摘要

The oxygen pressure and the substrate temperature during pulsed-laser deposition play a major role on the nature and properties of gallium oxide films. At moderate substrate temperature (673 K) and under high vacuum (10~(-7)mbar) a nanocomposite film composed of Ga metallic clusters embedded in a stoichiometric Ga_2O_3 matrix may be obtained without postdeposition annealing. The growth of such films is due to a phase separation of largely oxygen deficient metastable gallium oxide films Ga_2O_x (x = 2.3) into the most stable phases (Ga and Ga_2O_3) and occurs for particular growth conditions. The composition and the surface morphology of films as well as their electrical behaviour are interpreted according to the effects of the parameters governing this phase separation (oxygen deficiency and temperature). It is suggested that the initial step in the disproportionation reaction is the formation of stoichiometric Ga_2O_3 nanocrystallites in the metastable sub-oxide Ga_2O_x phase. The crystallization of such nanosize particles is governed by the local distribution of oxygen and gallium species impinging the substrate during the growth and allowing nucleation centre with the Ga_2O_3 composition.