Characterization of hydrogenated amorphous boron films prepared by electron cyclotron resonance plasma chemical vapor deposition method

Abstract

This paper presents characterization of amorphous boron (a-B) films prepared by the electron cyclotron resonance plasma chemical vapor deposition method using diborane (B2H6) and hydrogen mixtures. Compositional analyses show that hydrogen is the only impurity which influences film properties appreciably. The infrared absorption study shows that the hydrogen is incorporated into the film in the terminal bonding form. The hydrogen concentration has been estimated using the semiempirical equation given by Blum, Feldman, and Satkiewicz [Phys. Status Solidi A 41, 481 (1977)], which can be verified by the more fundamental principle. The infrared absorption study also shows that the amorphous films possess some short-range order related with the icosahedral structure. These observations allow us to consider that this film belongs to one of alloyed materials and is true hydrogenated a-B. In order to study the contributions of hydrogen to the film properties, variations of the color and the electrical resistivity of the film have been examined with changing the substrate temperature and the B2H6 concentration in source gases. These variations can be described with consistency in terms of the optical absorption edge. The films are a-B:H at substrate temperatures below 350 °C. The hydrogen incorporation results in increase in the resistivity and increase in the optical transparency. At substrate temperatures above 350 °C, the hydrogen is evolved from the film regardless of the B2H6 concentration, and intrinsic a-B films are obtained.