Epitaxial growth of Ge films on GaAs (285–415 °C) by laser photochemical vapor deposition

Abstract

Epitaxial Ge films have been grown on [001]GaAs by laser photochemical vapor deposition (LPVD) for substrate temperatures (Ts) in the 285≤Ts≤415 °C interval. Films 400–700 Å thick were grown at rates up to ∼1 Å s−1 (0.6–5 nm/min) by photodissociating GeH4 with an ArF (193 nm) laser in parallel geometry (i.e., laser beam passes above and parallel to substrate). The quality of the Ge/GaAs heterointerfaces has been examined by plan-view and cross-sectional transmission electron microscopy. Convergent beam electron diffraction, selected area diffraction patterns, and lattice images show the LPVD films to be epitaxial, whereas films grown in the absence of ultraviolet laser radiation (i.e., by conventional chemical vapor deposition) are amorphous (Ts=305 °C) or heavily defected polycrystalline (Ts=415 °C). Epitaxy apparently hinges on the laser production of a species which migrates more than 10–60 mean free paths to reach the substrate (or is collisionally transformed en route into a more stable species) and dramatically alters the surface chemistry. The large number of collisions involved points to the transformation of photochemically generated GeH2 or GeH3 into Ge2H6 as the key gas phase reaction.