Laser Photochemical Vapor Deposition of Ge Films (300 ≤ T ≤ 873 K) from GeH4: Roles of Ge2H6 and Ge

Abstract

AbstractThe photochemical growth of polycrystalline and amorphous Ge films on SiO2, GaAs and NaCl by photodissociating GeH4 with excimer laser radiation in parallel geometry is reported. For substrate temperatures (TS) below the pyrolytic threshold for GeH4 (553 K), two distinct regions of film growth are observed. In the 425< TS < 553 K range, the ultraviolet (UV) laser “seeds” the reactor with Ge2H6 which readily pyrolyzes at the surface, forming several monolayers of Ge which subsequently catalyze the pyrolysis of GeH4. The activation energy (Ea) in this region is the same as that for the normal CVD growth of Ge from GeH4 (Ea = 0.9 eV). If, however, the laser is pulsed throughout the film growth run, Ea falls by a factor of at least 2 and growth is observed for TS as low as 300 K. In this laser sustained region, film growth ceases in the absence of UV laser radiation. These results clearly demonstrate the ability of a UV laser to alter the reactor chemistry and dictate the species responsible for film growth.