Germanium phosphide coatings from the atmospheric pressure chemical vapour deposition of GeX 4 (X=Cl or Br) and PCyc hexH 2

Abstract

Atmospheric pressure chemical vapour deposition of germanium phosphide thin films was achieved on glass substrates from the reaction of GeCl 4 or GeBr 4 with PCyc hexH 2 at 600 °C. These coatings show good uniformity and surface coverage. They are reasonably adherent, passing the Scotch tape test. The films were translucent in appearance with regions of birefringence. The films were X-ray amorphous. Scanning electron microscopy showed surface morphologies consistent with an island growth mechanism. X-ray photoelectron spectroscopy binding energy shifts for GeP 1.00 were 1218.2 eV for Ge 2P 3 and 131.5 eV for P 2p 3/2. Energy dispersive X-ray analysis and electron probe studies gave elemental ratios that were in agreement indicating films which varied from being germanium rich (Ge 3P) to phosphorus rich (GeP 2), with negligible chlorine or bromine incorporation dependent on deposition conditions. No Raman scattering was observed. Sheet resistance measurements indicated the films were poor conductors. Optically the films showed poor reflectance (5–10%) and 60–80% total transmission from 400 to 1000 nm. UV–Vis spectroscopy indicated an indirect band gap of 1.1 eV. Contact angle measurements were in the range 60°–80° and showed no significant change after 60 min irradiation with 254 nm UV light.