Interface engineering for a stable chemical structure of oxidized-black phosphorus via self-reduction in AlOx atomic layer deposition

Abstract

We evaluated the change in the chemical structure between dielectrics (AlOx and HfOx) grown by atomic layer deposition (ALD) and oxidized black phosphorus (BP), as a function of air exposure time. Chemical and structural analyses of the oxidized phosphorus species (PxOy) were performed using atomic force microscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, first-principles density functional theory calculations, and the electrical characteristics of field-effect transistors (FETs). Based on the combined experiments and theoretical investigations, we clearly show that oxidized phosphorus species (PxOy, until exposed for 24 h) are significantly decreased (self-reduction) during the ALD of AlOx. In particular, the field effect characteristics of a FET device based on Al2O3/AlOx/oxidized BP improved significantly with enhanced electrical properties, a mobility of approximate to 253 cm(2) V-1 s(-1) and an on-off ratio of approximate to 10(5), compared to those of HfO2/HfOx/oxidized BP with a mobility of approximate to 97 cm(2) V-1 s(-1) and an on-off ratio of approximate to 10(3)-10(4). These distinct differences result from a significantly decreased interface trap density (D-it approximate to 10(11) cm(-2) eV(-1)) and subthreshold gate swing (SS approximate to 270 mV dec(-1)) in the BP device caused by the formation of stable energy states at the AlOx/oxidized BP interface, even with BP oxidized by air exposure.