STRUCTURAL AND ELECTRICAL CHARACTERIZATION OF EPITAXIAL CDF2 LAYERS GROWN ON SI(111) AND CAF2(111) SUBSTRATES

The wide band-gap, group-II fluoride CdF2 exhibits semiconducting prop erties when doped with some rare earth impurities and annealed under a ppropriate conditions. In addition, CdF2 is closely lattice matched to Si and epitaxial layers of CdF2 on Si are of potential interest for i ntegration of optoelectronic devices (such as light emitting diodes) w ith Si ULSI technology. In this work, approximately 300 nm-thick CdF2 films were grown on both Si and CaF2 substrates by molecular beam epit axy (MBE). Characterizations of the films by reflection high energy el ectron diffraction (RHEED), X-ray diffraction (XRD), Rutherford back-s cattering (RES) and atomic force microscopy (AFM) allowed the growth c onditions to be optimized. After growth, the structures were annealed in Cd vapor and their resistivity was measured by a simple two-probe t echnique both before and after annealing, After annealing in Cd vapor at 500 degrees C for 1 min, the resistivity of CdF2 films grown at 200 degrees C on CaF2 substrates dropped below 0.1 Ohm.cm from an as-grow n value of 10(6) Ohm.cm. On the other hand, films grown at 400 degrees C had an as-grown resistivity of about 10 Ohm.cm but did not decrease with annealing. (C) 1998 Elsevier Science B.V.