Interface GaAs - gallium fluoride thin film grown by fluorination: Electrical behaviour of the obtained MIS fluorinated GaAs structures

Abstract

Fluoride-GaAs(100) structures have been prepared by fluorination of the semiconductor under 1 bar of fluorine at different temperatures (Tf) and times (tf). The physico-chemical characterizations of the obtained samples have been deduced mainly from RBS, XPS and STEM experiments. It has been demonstrated that the bulk composition of the films formed at the surface of GaAs substrates is GaF3. At the fluoride-semiconductor interface, arsenic has been found to be bound with fluorine. In the case of thick films, it has been shown that the fluorine diffusion becomes inhomogeneous. Consequently, the thickness of the fluoride layers changes at different points on the structures. For Tf≥300°C, the capacitance voltage (C-V) characteristics of the obtained MIS fluorinated GaAs structures show that, using this passivation technique, an important modulation of the surface potential of the GaAs is obtained without hysteresis for a sweep frequency down to 10-2 Hz. The surface state density in the gap of GaAs is very low (Nss about 1011 eV-1 cm-2) To minimize the inhomogeneous fluorine diffusion effect, very thin layers of fluorine were grown by fluorination at the surface of GaAs and these structures were coated with a GaF3 thin film deposited by sublimation under vacuum. This process, which allows us to predict the thickness of the insulator, keeps the insulator-semiconductor interface in the state previously described.