Laser-induced plasmas for primary ion deposition of epitaxial Ge and Si films

Abstract

Epitaxial Ge and Si films have been grown by primary ion deposition from laser-induced plasmas. The plasmas were formed by focusing 15 ns, 107–108 W cm−2, pulses of 5 eV photons from a KrF excimer laser onto Ge or Si single crystal wafer targets. Time-of-flight, current-voltage, and film-thickness distribution measurements established that neutral atoms and ions were emitted from Ge targets with mean velocities of 1.0–1.6×106 cm s−1 (corresponding to average kinetic energies of 40 to 100 eV) in a distribution that was strongly peaked in the direction normal to the target surface. Macroscopic (∼1 μm diam) particles were also emitted. A shutter, synchronously triggered with the laser pulses through a delay circuit, was used as a velocity filter for removing from the beam particles with velocities up to 1.2×104 cm s−1. Epitaxial Ge films were grown on semi-insulating (100) GaAs substrates at temperatures between 300 and 450 °C and epitaxial Si was grown on (100) Si at 700 °C. Deposition rates were typically 0.5–1 μm h−1. Hall effect measurements carried out on the Ge/GeAs heterostructures showed that the Ge films, ∼1 μm thick, were p type with room temperature carrier concentrations of ∼1×1018 cm−3 and hole mobilities of ∼150 cm2/V s.