Molecular beam epitaxial growth and characterization of europium-doped calcium fluoride and fabrication of visible electroluminescent devices on silicon.

Abstract

An indirect band-gap precludes the possibility of efficient luminescence from Si. The widespread use of Si in electronics and rapid advances in Si device processing and design justifies the search for Si-based light emitters which can pave the way for Si-based opto-electronics. In this work, the molecular-beam-epitaxy (MBE) growth and characterization of Eu:CaF$\sb2$/Si(100) layers is presented and an electroluminescent device fabricated from this materials system is demonstrated. The MBE growth of the Eu:CaF$\sb2$ layers was carried out in an Intevac MOD GEN-II system. The post-growth surface ordering of Eu:CaF$\sb2$ was studied in situ by monitoring reflection-high-energy-electron-diffraction (RHEED) patterns. The surface morphology of the Eu:CaF$\sb2$ layers was studied ex situ using atomic-force-microscopy (AFM). X-ray photoelectron spectroscopy (XPS) was used to study the effect of high Eu content in the Eu:CaF$\sb2$ layers. Photoluminescence (PL) studies showed that up to 8.0 atomic % Eu can be incorporated into the MBE-grown layers without reduction in the integrated PL intensity at 10 K and 293 K from the Eu$\sp{2+}$ ions. The electrical properties of Eu:CaF$\sb2$ layers were inferred from the analysis of current-versus voltage and high-frequency capacitance versus voltage measurements on metal-insulator-semiconductor (MIS) structures fabricated from these layers. Visible electroluminescence: (EL) is observed at room temperature by current injection into MBE-grown Eu:CaF$\sb2$ layers containing 7.5 and 8.0 atomic percent Eu. The EL spectra are broad with peaks a pound 600 and 700 nm. The ability to generate EL using relatively small DC voltages makes this system promising for Si-based opto-electronics and display applications.